staging/lustre/osc: osc_lock_weight endless loop fix

[deliverable/linux.git] / drivers / staging / lustre / lustre / osc / osc_lock.c

/*
 * GPL HEADER START
 *
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 only,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License version 2 for more details (a copy is included
 * in the LICENSE file that accompanied this code).
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; If not, see
 * http://www.gnu.org/licenses/gpl-2.0.html
 *
 * GPL HEADER END
 */
/*
 * Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
 * Use is subject to license terms.
 *
 * Copyright (c) 2011, 2015, Intel Corporation.
 */
/*
 * This file is part of Lustre, http://www.lustre.org/
 * Lustre is a trademark of Sun Microsystems, Inc.
 *
 * Implementation of cl_lock for OSC layer.
 *
 *   Author: Nikita Danilov <nikita.danilov@sun.com>
 *   Author: Jinshan Xiong <jinshan.xiong@intel.com>
 */

#define DEBUG_SUBSYSTEM S_OSC

#include "../../include/linux/libcfs/libcfs.h"
/* fid_build_reg_res_name() */
#include "../include/lustre_fid.h"

#include "osc_cl_internal.h"

/** \addtogroup osc
 *  @{
 */

/*****************************************************************************
 *
 * Type conversions.
 *
 */

static const struct cl_lock_operations osc_lock_ops;
static const struct cl_lock_operations osc_lock_lockless_ops;
static void osc_lock_to_lockless(const struct lu_env *env,
                                 struct osc_lock *ols, int force);

int osc_lock_is_lockless(const struct osc_lock *olck)
{
        return (olck->ols_cl.cls_ops == &osc_lock_lockless_ops);
}

/**
 * Returns a weak pointer to the ldlm lock identified by a handle. Returned
 * pointer cannot be dereferenced, as lock is not protected from concurrent
 * reclaim. This function is a helper for osc_lock_invariant().
 */
static struct ldlm_lock *osc_handle_ptr(struct lustre_handle *handle)
{
        struct ldlm_lock *lock;

        lock = ldlm_handle2lock(handle);
        if (lock)
                LDLM_LOCK_PUT(lock);
        return lock;
}

/**
 * Invariant that has to be true all of the time.
 */
static int osc_lock_invariant(struct osc_lock *ols)
{
        struct ldlm_lock *lock = osc_handle_ptr(&ols->ols_handle);
        struct ldlm_lock *olock = ols->ols_dlmlock;
        int handle_used = lustre_handle_is_used(&ols->ols_handle);

        if (ergo(osc_lock_is_lockless(ols),
                 ols->ols_locklessable && !ols->ols_dlmlock))
                return 1;

        /*
         * If all the following "ergo"s are true, return 1, otherwise 0
         */
        if (!ergo(olock, handle_used))
                return 0;

        if (!ergo(olock, olock->l_handle.h_cookie == ols->ols_handle.cookie))
                return 0;

        if (!ergo(handle_used,
                  ergo(lock && olock, lock == olock) &&
                  ergo(!lock, !olock)))
                return 0;
        /*
         * Check that ->ols_handle and ->ols_dlmlock are consistent, but
         * take into account that they are set at the different time.
         */
        if (!ergo(ols->ols_state == OLS_CANCELLED,
                  !olock && !handle_used))
                return 0;
        /*
         * DLM lock is destroyed only after we have seen cancellation
         * ast.
         */
        if (!ergo(olock && ols->ols_state < OLS_CANCELLED,
                  !ldlm_is_destroyed(olock)))
                return 0;

        if (!ergo(ols->ols_state == OLS_GRANTED,
                  olock && olock->l_req_mode == olock->l_granted_mode &&
                  ols->ols_hold))
                return 0;
        return 1;
}

/*****************************************************************************
 *
 * Lock operations.
 *
 */

static void osc_lock_fini(const struct lu_env *env,
                          struct cl_lock_slice *slice)
{
        struct osc_lock *ols = cl2osc_lock(slice);

        LINVRNT(osc_lock_invariant(ols));
        LASSERT(!ols->ols_dlmlock);

        kmem_cache_free(osc_lock_kmem, ols);
}

static void osc_lock_build_policy(const struct lu_env *env,
                                  const struct cl_lock *lock,
                                  ldlm_policy_data_t *policy)
{
        const struct cl_lock_descr *d = &lock->cll_descr;

        osc_index2policy(policy, d->cld_obj, d->cld_start, d->cld_end);
        policy->l_extent.gid = d->cld_gid;
}

static __u64 osc_enq2ldlm_flags(__u32 enqflags)
{
        __u64 result = 0;

        LASSERT((enqflags & ~CEF_MASK) == 0);

        if (enqflags & CEF_NONBLOCK)
                result |= LDLM_FL_BLOCK_NOWAIT;
        if (enqflags & CEF_ASYNC)
                result |= LDLM_FL_HAS_INTENT;
        if (enqflags & CEF_DISCARD_DATA)
                result |= LDLM_FL_AST_DISCARD_DATA;
        if (enqflags & CEF_PEEK)
                result |= LDLM_FL_TEST_LOCK;
        return result;
}

/**
 * Updates object attributes from a lock value block (lvb) received together
 * with the DLM lock reply from the server. Copy of osc_update_enqueue()
 * logic.
 *
 * This can be optimized to not update attributes when lock is a result of a
 * local match.
 *
 * Called under lock and resource spin-locks.
 */
static void osc_lock_lvb_update(const struct lu_env *env,
                                struct osc_object *osc,
                                struct ldlm_lock *dlmlock,
                                struct ost_lvb *lvb)
{
        struct cl_object *obj = osc2cl(osc);
        struct lov_oinfo *oinfo = osc->oo_oinfo;
        struct cl_attr *attr = &osc_env_info(env)->oti_attr;
        unsigned valid;

        valid = CAT_BLOCKS | CAT_ATIME | CAT_CTIME | CAT_MTIME | CAT_SIZE;
        if (!lvb)
                lvb = dlmlock->l_lvb_data;

        cl_lvb2attr(attr, lvb);

        cl_object_attr_lock(obj);
        if (dlmlock) {
                __u64 size;

                check_res_locked(dlmlock->l_resource);
                LASSERT(lvb == dlmlock->l_lvb_data);
                size = lvb->lvb_size;

                /* Extend KMS up to the end of this lock and no further
                 * A lock on [x,y] means a KMS of up to y + 1 bytes!
                 */
                if (size > dlmlock->l_policy_data.l_extent.end)
                        size = dlmlock->l_policy_data.l_extent.end + 1;
                if (size >= oinfo->loi_kms) {
                        LDLM_DEBUG(dlmlock, "lock acquired, setting rss=%llu, kms=%llu",
                                   lvb->lvb_size, size);
                        valid |= CAT_KMS;
                        attr->cat_kms = size;
                } else {
                        LDLM_DEBUG(dlmlock, "lock acquired, setting rss=%llu; leaving kms=%llu, end=%llu",
                                   lvb->lvb_size, oinfo->loi_kms,
                                   dlmlock->l_policy_data.l_extent.end);
                }
                ldlm_lock_allow_match_locked(dlmlock);
        }

        cl_object_attr_set(env, obj, attr, valid);
        cl_object_attr_unlock(obj);
}

static void osc_lock_granted(const struct lu_env *env, struct osc_lock *oscl,
                             struct lustre_handle *lockh, bool lvb_update)
{
        struct ldlm_lock *dlmlock;

        dlmlock = ldlm_handle2lock_long(lockh, 0);
        LASSERT(dlmlock);

        /* lock reference taken by ldlm_handle2lock_long() is
         * owned by osc_lock and released in osc_lock_detach()
         */
        lu_ref_add(&dlmlock->l_reference, "osc_lock", oscl);
        oscl->ols_has_ref = 1;

        LASSERT(!oscl->ols_dlmlock);
        oscl->ols_dlmlock = dlmlock;

        /* This may be a matched lock for glimpse request, do not hold
         * lock reference in that case.
         */
        if (!oscl->ols_glimpse) {
                /* hold a refc for non glimpse lock which will
                 * be released in osc_lock_cancel()
                 */
                lustre_handle_copy(&oscl->ols_handle, lockh);
                ldlm_lock_addref(lockh, oscl->ols_einfo.ei_mode);
                oscl->ols_hold = 1;
        }

        /* Lock must have been granted. */
        lock_res_and_lock(dlmlock);
        if (dlmlock->l_granted_mode == dlmlock->l_req_mode) {
                struct ldlm_extent *ext = &dlmlock->l_policy_data.l_extent;
                struct cl_lock_descr *descr = &oscl->ols_cl.cls_lock->cll_descr;

                /* extend the lock extent, otherwise it will have problem when
                 * we decide whether to grant a lockless lock.
                 */
                descr->cld_mode = osc_ldlm2cl_lock(dlmlock->l_granted_mode);
                descr->cld_start = cl_index(descr->cld_obj, ext->start);
                descr->cld_end = cl_index(descr->cld_obj, ext->end);
                descr->cld_gid = ext->gid;

                /* no lvb update for matched lock */
                if (lvb_update) {
                        LASSERT(oscl->ols_flags & LDLM_FL_LVB_READY);
                        osc_lock_lvb_update(env, cl2osc(oscl->ols_cl.cls_obj),
                                            dlmlock, NULL);
                }
                LINVRNT(osc_lock_invariant(oscl));
        }
        unlock_res_and_lock(dlmlock);

        LASSERT(oscl->ols_state != OLS_GRANTED);
        oscl->ols_state = OLS_GRANTED;
}

/**
 * Lock upcall function that is executed either when a reply to ENQUEUE rpc is
 * received from a server, or after osc_enqueue_base() matched a local DLM
 * lock.
 */
static int osc_lock_upcall(void *cookie, struct lustre_handle *lockh,
                           int errcode)
{
        struct osc_lock *oscl = cookie;
        struct cl_lock_slice *slice = &oscl->ols_cl;
        struct lu_env *env;
        struct cl_env_nest nest;
        int rc;

        env = cl_env_nested_get(&nest);
        /* should never happen, similar to osc_ldlm_blocking_ast(). */
        LASSERT(!IS_ERR(env));

        rc = ldlm_error2errno(errcode);
        if (oscl->ols_state == OLS_ENQUEUED) {
                oscl->ols_state = OLS_UPCALL_RECEIVED;
        } else if (oscl->ols_state == OLS_CANCELLED) {
                rc = -EIO;
        } else {
                CERROR("Impossible state: %d\n", oscl->ols_state);
                LBUG();
        }

        if (rc == 0)
                osc_lock_granted(env, oscl, lockh, errcode == ELDLM_OK);

        /* Error handling, some errors are tolerable. */
        if (oscl->ols_locklessable && rc == -EUSERS) {
                /* This is a tolerable error, turn this lock into
                 * lockless lock.
                 */
                osc_object_set_contended(cl2osc(slice->cls_obj));
                LASSERT(slice->cls_ops == &osc_lock_ops);

                /* Change this lock to ldlmlock-less lock. */
                osc_lock_to_lockless(env, oscl, 1);
                oscl->ols_state = OLS_GRANTED;
                rc = 0;
        } else if (oscl->ols_glimpse && rc == -ENAVAIL) {
                LASSERT(oscl->ols_flags & LDLM_FL_LVB_READY);
                osc_lock_lvb_update(env, cl2osc(slice->cls_obj),
                                    NULL, &oscl->ols_lvb);
                /* Hide the error. */
                rc = 0;
        }

        if (oscl->ols_owner)
                cl_sync_io_note(env, oscl->ols_owner, rc);
        cl_env_nested_put(&nest, env);

        return rc;
}

static int osc_lock_upcall_agl(void *cookie, struct lustre_handle *lockh,
                               int errcode)
{
        struct osc_object *osc = cookie;
        struct ldlm_lock *dlmlock;
        struct lu_env *env;
        struct cl_env_nest nest;

        env = cl_env_nested_get(&nest);
        LASSERT(!IS_ERR(env));

        if (errcode == ELDLM_LOCK_MATCHED) {
                errcode = ELDLM_OK;
                goto out;
        }

        if (errcode != ELDLM_OK)
                goto out;

        dlmlock = ldlm_handle2lock(lockh);
        LASSERT(dlmlock);

        lock_res_and_lock(dlmlock);
        LASSERT(dlmlock->l_granted_mode == dlmlock->l_req_mode);

        /* there is no osc_lock associated with AGL lock */
        osc_lock_lvb_update(env, osc, dlmlock, NULL);

        unlock_res_and_lock(dlmlock);
        LDLM_LOCK_PUT(dlmlock);

out:
        cl_object_put(env, osc2cl(osc));
        cl_env_nested_put(&nest, env);
        return ldlm_error2errno(errcode);
}

static int osc_lock_flush(struct osc_object *obj, pgoff_t start, pgoff_t end,
                          enum cl_lock_mode mode, int discard)
{
        struct lu_env *env;
        struct cl_env_nest nest;
        int rc = 0;
        int rc2 = 0;

        env = cl_env_nested_get(&nest);
        if (IS_ERR(env))
                return PTR_ERR(env);

        if (mode == CLM_WRITE) {
                rc = osc_cache_writeback_range(env, obj, start, end, 1,
                                               discard);
                CDEBUG(D_CACHE, "object %p: [%lu -> %lu] %d pages were %s.\n",
                       obj, start, end, rc,
                       discard ? "discarded" : "written back");
                if (rc > 0)
                        rc = 0;
        }

        rc2 = osc_lock_discard_pages(env, obj, start, end, mode);
        if (rc == 0 && rc2 < 0)
                rc = rc2;

        cl_env_nested_put(&nest, env);
        return rc;
}

/**
 * Helper for osc_dlm_blocking_ast() handling discrepancies between cl_lock
 * and ldlm_lock caches.
 */
static int osc_dlm_blocking_ast0(const struct lu_env *env,
                                 struct ldlm_lock *dlmlock,
                                 void *data, int flag)
{
        struct cl_object *obj = NULL;
        int result = 0;
        int discard;
        enum cl_lock_mode mode = CLM_READ;

        LASSERT(flag == LDLM_CB_CANCELING);

        lock_res_and_lock(dlmlock);
        if (dlmlock->l_granted_mode != dlmlock->l_req_mode) {
                dlmlock->l_ast_data = NULL;
                unlock_res_and_lock(dlmlock);
                return 0;
        }

        discard = ldlm_is_discard_data(dlmlock);
        if (dlmlock->l_granted_mode & (LCK_PW | LCK_GROUP))
                mode = CLM_WRITE;

        if (dlmlock->l_ast_data) {
                obj = osc2cl(dlmlock->l_ast_data);
                dlmlock->l_ast_data = NULL;

                cl_object_get(obj);
        }

        unlock_res_and_lock(dlmlock);

        /* if l_ast_data is NULL, the dlmlock was enqueued by AGL or
         * the object has been destroyed.
         */
        if (obj) {
                struct ldlm_extent *extent = &dlmlock->l_policy_data.l_extent;
                struct cl_attr *attr = &osc_env_info(env)->oti_attr;
                __u64 old_kms;

                /* Destroy pages covered by the extent of the DLM lock */
                result = osc_lock_flush(cl2osc(obj),
                                        cl_index(obj, extent->start),
                                        cl_index(obj, extent->end),
                                        mode, discard);

                /* losing a lock, update kms */
                lock_res_and_lock(dlmlock);
                cl_object_attr_lock(obj);
                /* Must get the value under the lock to avoid race. */
                old_kms = cl2osc(obj)->oo_oinfo->loi_kms;
                /* Update the kms. Need to loop all granted locks.
                 * Not a problem for the client
                 */
                attr->cat_kms = ldlm_extent_shift_kms(dlmlock, old_kms);

                cl_object_attr_set(env, obj, attr, CAT_KMS);
                cl_object_attr_unlock(obj);
                unlock_res_and_lock(dlmlock);

                cl_object_put(env, obj);
        }
        return result;
}

/**
 * Blocking ast invoked by ldlm when dlm lock is either blocking progress of
 * some other lock, or is canceled. This function is installed as a
 * ldlm_lock::l_blocking_ast() for client extent locks.
 *
 * Control flow is tricky, because ldlm uses the same call-back
 * (ldlm_lock::l_blocking_ast()) for both blocking and cancellation ast's.
 *
 * \param dlmlock lock for which ast occurred.
 *
 * \param new description of a conflicting lock in case of blocking ast.
 *
 * \param data value of dlmlock->l_ast_data
 *
 * \param flag LDLM_CB_BLOCKING or LDLM_CB_CANCELING. Used to distinguish
 *           cancellation and blocking ast's.
 *
 * Possible use cases:
 *
 *     - ldlm calls dlmlock->l_blocking_ast(..., LDLM_CB_CANCELING) to cancel
 *       lock due to lock lru pressure, or explicit user request to purge
 *       locks.
 *
 *     - ldlm calls dlmlock->l_blocking_ast(..., LDLM_CB_BLOCKING) to notify
 *       us that dlmlock conflicts with another lock that some client is
 *       enqueing. Lock is canceled.
 *
 *         - cl_lock_cancel() is called. osc_lock_cancel() calls
 *           ldlm_cli_cancel() that calls
 *
 *                dlmlock->l_blocking_ast(..., LDLM_CB_CANCELING)
 *
 *           recursively entering osc_ldlm_blocking_ast().
 *
 *     - client cancels lock voluntary (e.g., as a part of early cancellation):
 *
 *         cl_lock_cancel()->
 *           osc_lock_cancel()->
 *             ldlm_cli_cancel()->
 *               dlmlock->l_blocking_ast(..., LDLM_CB_CANCELING)
 *
 */
static int osc_ldlm_blocking_ast(struct ldlm_lock *dlmlock,
                                 struct ldlm_lock_desc *new, void *data,
                                 int flag)
{
        int result = 0;

        switch (flag) {
        case LDLM_CB_BLOCKING: {
                struct lustre_handle lockh;

                ldlm_lock2handle(dlmlock, &lockh);
                result = ldlm_cli_cancel(&lockh, LCF_ASYNC);
                if (result == -ENODATA)
                        result = 0;
                break;
        }
        case LDLM_CB_CANCELING: {
                struct lu_env *env;
                struct cl_env_nest nest;

                /*
                 * This can be called in the context of outer IO, e.g.,
                 *
                 *     osc_enqueue_base()->...
                 *       ->ldlm_prep_elc_req()->...
                 *         ->ldlm_cancel_callback()->...
                 *           ->osc_ldlm_blocking_ast()
                 *
                 * new environment has to be created to not corrupt outer
                 * context.
                 */
                env = cl_env_nested_get(&nest);
                if (IS_ERR(env)) {
                        result = PTR_ERR(env);
                        break;
                }

                result = osc_dlm_blocking_ast0(env, dlmlock, data, flag);
                cl_env_nested_put(&nest, env);
                break;
                }
        default:
                LBUG();
        }
        return result;
}

static int osc_ldlm_glimpse_ast(struct ldlm_lock *dlmlock, void *data)
{
        struct ptlrpc_request *req = data;
        struct cl_env_nest nest;
        struct lu_env *env;
        struct ost_lvb *lvb;
        struct req_capsule *cap;
        int result;

        LASSERT(lustre_msg_get_opc(req->rq_reqmsg) == LDLM_GL_CALLBACK);

        env = cl_env_nested_get(&nest);
        if (!IS_ERR(env)) {
                struct cl_object *obj = NULL;

                lock_res_and_lock(dlmlock);
                if (dlmlock->l_ast_data) {
                        obj = osc2cl(dlmlock->l_ast_data);
                        cl_object_get(obj);
                }
                unlock_res_and_lock(dlmlock);

                if (obj) {
                        /* Do not grab the mutex of cl_lock for glimpse.
                         * See LU-1274 for details.
                         * BTW, it's okay for cl_lock to be cancelled during
                         * this period because server can handle this race.
                         * See ldlm_server_glimpse_ast() for details.
                         * cl_lock_mutex_get(env, lock);
                         */
                        cap = &req->rq_pill;
                        req_capsule_extend(cap, &RQF_LDLM_GL_CALLBACK);
                        req_capsule_set_size(cap, &RMF_DLM_LVB, RCL_SERVER,
                                             sizeof(*lvb));
                        result = req_capsule_server_pack(cap);
                        if (result == 0) {
                                lvb = req_capsule_server_get(cap, &RMF_DLM_LVB);
                                result = cl_object_glimpse(env, obj, lvb);
                        }
                        if (!exp_connect_lvb_type(req->rq_export))
                                req_capsule_shrink(&req->rq_pill,
                                                   &RMF_DLM_LVB,
                                                   sizeof(struct ost_lvb_v1),
                                                   RCL_SERVER);
                        cl_object_put(env, obj);
                } else {
                        /*
                         * These errors are normal races, so we don't want to
                         * fill the console with messages by calling
                         * ptlrpc_error()
                         */
                        lustre_pack_reply(req, 1, NULL, NULL);
                        result = -ELDLM_NO_LOCK_DATA;
                }
                cl_env_nested_put(&nest, env);
        } else {
                result = PTR_ERR(env);
        }
        req->rq_status = result;
        return result;
}

static int weigh_cb(const struct lu_env *env, struct cl_io *io,
                    struct osc_page *ops, void *cbdata)
{
        struct cl_page *page = ops->ops_cl.cpl_page;

        if (cl_page_is_vmlocked(env, page) ||
            PageDirty(page->cp_vmpage) || PageWriteback(page->cp_vmpage)
           )
                return CLP_GANG_ABORT;

        *(pgoff_t *)cbdata = osc_index(ops) + 1;
        return CLP_GANG_OKAY;
}

static unsigned long osc_lock_weight(const struct lu_env *env,
                                     struct osc_object *oscobj,
                                     struct ldlm_extent *extent)
{
        struct cl_io *io = &osc_env_info(env)->oti_io;
        struct cl_object *obj = cl_object_top(&oscobj->oo_cl);
        pgoff_t page_index;
        int result;

        io->ci_obj = obj;
        io->ci_ignore_layout = 1;
        result = cl_io_init(env, io, CIT_MISC, io->ci_obj);
        if (result != 0)
                return result;

        page_index = cl_index(obj, extent->start);
        do {
                result = osc_page_gang_lookup(env, io, oscobj,
                                              page_index,
                                              cl_index(obj, extent->end),
                                              weigh_cb, (void *)&page_index);
                if (result == CLP_GANG_ABORT)
                        break;
                if (result == CLP_GANG_RESCHED)
                        cond_resched();
        } while (result != CLP_GANG_OKAY);
        cl_io_fini(env, io);

        return result == CLP_GANG_ABORT ? 1 : 0;
}

/**
 * Get the weight of dlm lock for early cancellation.
 */
unsigned long osc_ldlm_weigh_ast(struct ldlm_lock *dlmlock)
{
        struct cl_env_nest       nest;
        struct lu_env           *env;
        struct osc_object       *obj;
        struct osc_lock         *oscl;
        unsigned long            weight;
        bool                     found = false;

        might_sleep();
        /*
         * osc_ldlm_weigh_ast has a complex context since it might be called
         * because of lock canceling, or from user's input. We have to make
         * a new environment for it. Probably it is implementation safe to use
         * the upper context because cl_lock_put don't modify environment
         * variables. But just in case ..
         */
        env = cl_env_nested_get(&nest);
        if (IS_ERR(env))
                /* Mostly because lack of memory, do not eliminate this lock */
                return 1;

        LASSERT(dlmlock->l_resource->lr_type == LDLM_EXTENT);
        obj = dlmlock->l_ast_data;
        if (obj) {
                weight = 1;
                goto out;
        }

        spin_lock(&obj->oo_ol_spin);
        list_for_each_entry(oscl, &obj->oo_ol_list, ols_nextlock_oscobj) {
                if (oscl->ols_dlmlock && oscl->ols_dlmlock != dlmlock)
                        continue;
                found = true;
        }
        spin_unlock(&obj->oo_ol_spin);
        if (found) {
                /*
                 * If the lock is being used by an IO, definitely not cancel it.
                 */
                weight = 1;
                goto out;
        }

        weight = osc_lock_weight(env, obj, &dlmlock->l_policy_data.l_extent);

out:
        cl_env_nested_put(&nest, env);
        return weight;
}

static void osc_lock_build_einfo(const struct lu_env *env,
                                 const struct cl_lock *lock,
                                 struct osc_object *osc,
                                 struct ldlm_enqueue_info *einfo)
{
        einfo->ei_type = LDLM_EXTENT;
        einfo->ei_mode   = osc_cl_lock2ldlm(lock->cll_descr.cld_mode);
        einfo->ei_cb_bl = osc_ldlm_blocking_ast;
        einfo->ei_cb_cp  = ldlm_completion_ast;
        einfo->ei_cb_gl = osc_ldlm_glimpse_ast;
        einfo->ei_cbdata = osc; /* value to be put into ->l_ast_data */
}

/**
 * Determine if the lock should be converted into a lockless lock.
 *
 * Steps to check:
 * - if the lock has an explicit requirement for a non-lockless lock;
 * - if the io lock request type ci_lockreq;
 * - send the enqueue rpc to ost to make the further decision;
 * - special treat to truncate lockless lock
 *
 *  Additional policy can be implemented here, e.g., never do lockless-io
 *  for large extents.
 */
static void osc_lock_to_lockless(const struct lu_env *env,
                                 struct osc_lock *ols, int force)
{
        struct cl_lock_slice *slice = &ols->ols_cl;

        LASSERT(ols->ols_state == OLS_NEW ||
                ols->ols_state == OLS_UPCALL_RECEIVED);

        if (force) {
                ols->ols_locklessable = 1;
                slice->cls_ops = &osc_lock_lockless_ops;
        } else {
                struct osc_io *oio = osc_env_io(env);
                struct cl_io *io = oio->oi_cl.cis_io;
                struct cl_object *obj = slice->cls_obj;
                struct osc_object *oob = cl2osc(obj);
                const struct osc_device *osd = lu2osc_dev(obj->co_lu.lo_dev);
                struct obd_connect_data *ocd;

                LASSERT(io->ci_lockreq == CILR_MANDATORY ||
                        io->ci_lockreq == CILR_MAYBE ||
                        io->ci_lockreq == CILR_NEVER);

                ocd = &class_exp2cliimp(osc_export(oob))->imp_connect_data;
                ols->ols_locklessable = (io->ci_type != CIT_SETATTR) &&
                                (io->ci_lockreq == CILR_MAYBE) &&
                                (ocd->ocd_connect_flags & OBD_CONNECT_SRVLOCK);
                if (io->ci_lockreq == CILR_NEVER ||
                        /* lockless IO */
                    (ols->ols_locklessable && osc_object_is_contended(oob)) ||
                        /* lockless truncate */
                    (cl_io_is_trunc(io) &&
                     (ocd->ocd_connect_flags & OBD_CONNECT_TRUNCLOCK) &&
                      osd->od_lockless_truncate)) {
                        ols->ols_locklessable = 1;
                        slice->cls_ops = &osc_lock_lockless_ops;
                }
        }
        LASSERT(ergo(ols->ols_glimpse, !osc_lock_is_lockless(ols)));
}

static bool osc_lock_compatible(const struct osc_lock *qing,
                                const struct osc_lock *qed)
{
        struct cl_lock_descr *qed_descr = &qed->ols_cl.cls_lock->cll_descr;
        struct cl_lock_descr *qing_descr = &qing->ols_cl.cls_lock->cll_descr;

        if (qed->ols_glimpse)
                return true;

        if (qing_descr->cld_mode == CLM_READ && qed_descr->cld_mode == CLM_READ)
                return true;

        if (qed->ols_state < OLS_GRANTED)
                return true;

        if (qed_descr->cld_mode  >= qing_descr->cld_mode &&
            qed_descr->cld_start <= qing_descr->cld_start &&
            qed_descr->cld_end   >= qing_descr->cld_end)
                return true;

        return false;
}

static void osc_lock_wake_waiters(const struct lu_env *env,
                                  struct osc_object *osc,
                                  struct osc_lock *oscl)
{
        spin_lock(&osc->oo_ol_spin);
        list_del_init(&oscl->ols_nextlock_oscobj);
        spin_unlock(&osc->oo_ol_spin);

        spin_lock(&oscl->ols_lock);
        while (!list_empty(&oscl->ols_waiting_list)) {
                struct osc_lock *scan;

                scan = list_entry(oscl->ols_waiting_list.next, struct osc_lock,
                                  ols_wait_entry);
                list_del_init(&scan->ols_wait_entry);

                cl_sync_io_note(env, scan->ols_owner, 0);
        }
        spin_unlock(&oscl->ols_lock);
}

static void osc_lock_enqueue_wait(const struct lu_env *env,
                                  struct osc_object *obj,
                                  struct osc_lock *oscl)
{
        struct osc_lock *tmp_oscl;
        struct cl_lock_descr *need = &oscl->ols_cl.cls_lock->cll_descr;
        struct cl_sync_io *waiter = &osc_env_info(env)->oti_anchor;

        spin_lock(&obj->oo_ol_spin);
        list_add_tail(&oscl->ols_nextlock_oscobj, &obj->oo_ol_list);

restart:
        list_for_each_entry(tmp_oscl, &obj->oo_ol_list,
                            ols_nextlock_oscobj) {
                struct cl_lock_descr *descr;

                if (tmp_oscl == oscl)
                        break;

                descr = &tmp_oscl->ols_cl.cls_lock->cll_descr;
                if (descr->cld_start > need->cld_end ||
                    descr->cld_end   < need->cld_start)
                        continue;

                /* We're not supposed to give up group lock */
                if (descr->cld_mode == CLM_GROUP)
                        break;

                if (!osc_lock_is_lockless(oscl) &&
                    osc_lock_compatible(oscl, tmp_oscl))
                        continue;

                /* wait for conflicting lock to be canceled */
                cl_sync_io_init(waiter, 1, cl_sync_io_end);
                oscl->ols_owner = waiter;

                spin_lock(&tmp_oscl->ols_lock);
                /* add oscl into tmp's ols_waiting list */
                list_add_tail(&oscl->ols_wait_entry,
                              &tmp_oscl->ols_waiting_list);
                spin_unlock(&tmp_oscl->ols_lock);

                spin_unlock(&obj->oo_ol_spin);
                (void)cl_sync_io_wait(env, waiter, 0);

                spin_lock(&obj->oo_ol_spin);
                oscl->ols_owner = NULL;
                goto restart;
        }
        spin_unlock(&obj->oo_ol_spin);
}

/**
 * Implementation of cl_lock_operations::clo_enqueue() method for osc
 * layer. This initiates ldlm enqueue:
 *
 *     - cancels conflicting locks early (osc_lock_enqueue_wait());
 *
 *     - calls osc_enqueue_base() to do actual enqueue.
 *
 * osc_enqueue_base() is supplied with an upcall function that is executed
 * when lock is received either after a local cached ldlm lock is matched, or
 * when a reply from the server is received.
 *
 * This function does not wait for the network communication to complete.
 */
static int osc_lock_enqueue(const struct lu_env *env,
                            const struct cl_lock_slice *slice,
                            struct cl_io *unused, struct cl_sync_io *anchor)
{
        struct osc_thread_info *info = osc_env_info(env);
        struct osc_io *oio = osc_env_io(env);
        struct osc_object *osc = cl2osc(slice->cls_obj);
        struct osc_lock *oscl = cl2osc_lock(slice);
        struct cl_lock *lock = slice->cls_lock;
        struct ldlm_res_id *resname = &info->oti_resname;
        ldlm_policy_data_t *policy = &info->oti_policy;
        osc_enqueue_upcall_f upcall = osc_lock_upcall;
        void *cookie = oscl;
        bool async = false;
        int result;

        LASSERTF(ergo(oscl->ols_glimpse, lock->cll_descr.cld_mode <= CLM_READ),
                 "lock = %p, ols = %p\n", lock, oscl);

        if (oscl->ols_state == OLS_GRANTED)
                return 0;

        if (oscl->ols_flags & LDLM_FL_TEST_LOCK)
                goto enqueue_base;

        if (oscl->ols_glimpse) {
                LASSERT(equi(oscl->ols_agl, !anchor));
                async = true;
                goto enqueue_base;
        }

        osc_lock_enqueue_wait(env, osc, oscl);

        /* we can grant lockless lock right after all conflicting locks
         * are canceled.
         */
        if (osc_lock_is_lockless(oscl)) {
                oscl->ols_state = OLS_GRANTED;
                oio->oi_lockless = 1;
                return 0;
        }

enqueue_base:
        oscl->ols_state = OLS_ENQUEUED;
        if (anchor) {
                atomic_inc(&anchor->csi_sync_nr);
                oscl->ols_owner = anchor;
        }

        /**
         * DLM lock's ast data must be osc_object;
         * if glimpse or AGL lock, async of osc_enqueue_base() must be true,
         * DLM's enqueue callback set to osc_lock_upcall() with cookie as
         * osc_lock.
         */
        ostid_build_res_name(&osc->oo_oinfo->loi_oi, resname);
        osc_lock_build_einfo(env, lock, osc, &oscl->ols_einfo);
        osc_lock_build_policy(env, lock, policy);
        if (oscl->ols_agl) {
                oscl->ols_einfo.ei_cbdata = NULL;
                /* hold a reference for callback */
                cl_object_get(osc2cl(osc));
                upcall = osc_lock_upcall_agl;
                cookie = osc;
        }
        result = osc_enqueue_base(osc_export(osc), resname, &oscl->ols_flags,
                                  policy, &oscl->ols_lvb,
                                  osc->oo_oinfo->loi_kms_valid,
                                  upcall, cookie,
                                  &oscl->ols_einfo, PTLRPCD_SET, async,
                                  oscl->ols_agl);
        if (result != 0) {
                oscl->ols_state = OLS_CANCELLED;
                osc_lock_wake_waiters(env, osc, oscl);

                /* hide error for AGL lock. */
                if (oscl->ols_agl) {
                        cl_object_put(env, osc2cl(osc));
                        result = 0;
                }
                if (anchor)
                        cl_sync_io_note(env, anchor, result);
        } else {
                if (osc_lock_is_lockless(oscl)) {
                        oio->oi_lockless = 1;
                } else if (!async) {
                        LASSERT(oscl->ols_state == OLS_GRANTED);
                        LASSERT(oscl->ols_hold);
                        LASSERT(oscl->ols_dlmlock);
                }
        }
        return result;
}

/**
 * Breaks a link between osc_lock and dlm_lock.
 */
static void osc_lock_detach(const struct lu_env *env, struct osc_lock *olck)
{
        struct ldlm_lock *dlmlock;

        dlmlock = olck->ols_dlmlock;
        if (!dlmlock)
                return;

        if (olck->ols_hold) {
                olck->ols_hold = 0;
                osc_cancel_base(&olck->ols_handle, olck->ols_einfo.ei_mode);
                olck->ols_handle.cookie = 0ULL;
        }

        olck->ols_dlmlock = NULL;

        /* release a reference taken in osc_lock_upcall(). */
        LASSERT(olck->ols_has_ref);
        lu_ref_del(&dlmlock->l_reference, "osc_lock", olck);
        LDLM_LOCK_RELEASE(dlmlock);
        olck->ols_has_ref = 0;
}

/**
 * Implements cl_lock_operations::clo_cancel() method for osc layer. This is
 * called (as part of cl_lock_cancel()) when lock is canceled either voluntary
 * (LRU pressure, early cancellation, umount, etc.) or due to the conflict
 * with some other lock some where in the cluster. This function does the
 * following:
 *
 *     - invalidates all pages protected by this lock (after sending dirty
 *       ones to the server, as necessary);
 *
 *     - decref's underlying ldlm lock;
 *
 *     - cancels ldlm lock (ldlm_cli_cancel()).
 */
static void osc_lock_cancel(const struct lu_env *env,
                            const struct cl_lock_slice *slice)
{
        struct osc_object *obj  = cl2osc(slice->cls_obj);
        struct osc_lock *oscl = cl2osc_lock(slice);

        LINVRNT(osc_lock_invariant(oscl));

        osc_lock_detach(env, oscl);
        oscl->ols_state = OLS_CANCELLED;
        oscl->ols_flags &= ~LDLM_FL_LVB_READY;

        osc_lock_wake_waiters(env, obj, oscl);
}

static int osc_lock_print(const struct lu_env *env, void *cookie,
                          lu_printer_t p, const struct cl_lock_slice *slice)
{
        struct osc_lock *lock = cl2osc_lock(slice);

        (*p)(env, cookie, "%p %#16llx %#llx %d %p ",
             lock->ols_dlmlock, lock->ols_flags, lock->ols_handle.cookie,
             lock->ols_state, lock->ols_owner);
        osc_lvb_print(env, cookie, p, &lock->ols_lvb);
        return 0;
}

static const struct cl_lock_operations osc_lock_ops = {
        .clo_fini    = osc_lock_fini,
        .clo_enqueue = osc_lock_enqueue,
        .clo_cancel  = osc_lock_cancel,
        .clo_print   = osc_lock_print,
};

static void osc_lock_lockless_cancel(const struct lu_env *env,
                                     const struct cl_lock_slice *slice)
{
        struct osc_lock *ols = cl2osc_lock(slice);
        struct osc_object *osc = cl2osc(slice->cls_obj);
        struct cl_lock_descr *descr = &slice->cls_lock->cll_descr;
        int result;

        LASSERT(!ols->ols_dlmlock);
        result = osc_lock_flush(osc, descr->cld_start, descr->cld_end,
                                descr->cld_mode, 0);
        if (result)
                CERROR("Pages for lockless lock %p were not purged(%d)\n",
                       ols, result);

        osc_lock_wake_waiters(env, osc, ols);
}

static const struct cl_lock_operations osc_lock_lockless_ops = {
        .clo_fini       = osc_lock_fini,
        .clo_enqueue    = osc_lock_enqueue,
        .clo_cancel     = osc_lock_lockless_cancel,
        .clo_print      = osc_lock_print
};

static void osc_lock_set_writer(const struct lu_env *env,
                                const struct cl_io *io,
                                struct cl_object *obj, struct osc_lock *oscl)
{
        struct cl_lock_descr *descr = &oscl->ols_cl.cls_lock->cll_descr;
        pgoff_t io_start;
        pgoff_t io_end;

        if (!cl_object_same(io->ci_obj, obj))
                return;

        if (likely(io->ci_type == CIT_WRITE)) {
                io_start = cl_index(obj, io->u.ci_rw.crw_pos);
                io_end = cl_index(obj, io->u.ci_rw.crw_pos +
                                  io->u.ci_rw.crw_count - 1);
                if (cl_io_is_append(io)) {
                        io_start = 0;
                        io_end = CL_PAGE_EOF;
                }
        } else {
                LASSERT(cl_io_is_mkwrite(io));
                io_start = io->u.ci_fault.ft_index;
                io_end = io->u.ci_fault.ft_index;
        }

        if (descr->cld_mode >= CLM_WRITE &&
            descr->cld_start <= io_start && descr->cld_end >= io_end) {
                struct osc_io *oio = osc_env_io(env);

                /* There must be only one lock to match the write region */
                LASSERT(!oio->oi_write_osclock);
                oio->oi_write_osclock = oscl;
        }
}

int osc_lock_init(const struct lu_env *env,
                  struct cl_object *obj, struct cl_lock *lock,
                  const struct cl_io *io)
{
        struct osc_lock *oscl;
        __u32 enqflags = lock->cll_descr.cld_enq_flags;

        oscl = kmem_cache_zalloc(osc_lock_kmem, GFP_NOFS);
        if (!oscl)
                return -ENOMEM;

        oscl->ols_state = OLS_NEW;
        spin_lock_init(&oscl->ols_lock);
        INIT_LIST_HEAD(&oscl->ols_waiting_list);
        INIT_LIST_HEAD(&oscl->ols_wait_entry);
        INIT_LIST_HEAD(&oscl->ols_nextlock_oscobj);

        oscl->ols_flags = osc_enq2ldlm_flags(enqflags);
        oscl->ols_agl = !!(enqflags & CEF_AGL);
        if (oscl->ols_agl)
                oscl->ols_flags |= LDLM_FL_BLOCK_NOWAIT;
        if (oscl->ols_flags & LDLM_FL_HAS_INTENT) {
                oscl->ols_flags |= LDLM_FL_BLOCK_GRANTED;
                oscl->ols_glimpse = 1;
        }

        cl_lock_slice_add(lock, &oscl->ols_cl, obj, &osc_lock_ops);

        if (!(enqflags & CEF_MUST))
                /* try to convert this lock to a lockless lock */
                osc_lock_to_lockless(env, oscl, (enqflags & CEF_NEVER));
        if (oscl->ols_locklessable && !(enqflags & CEF_DISCARD_DATA))
                oscl->ols_flags |= LDLM_FL_DENY_ON_CONTENTION;

        if (io->ci_type == CIT_WRITE || cl_io_is_mkwrite(io))
                osc_lock_set_writer(env, io, obj, oscl);


        LDLM_DEBUG_NOLOCK("lock %p, osc lock %p, flags %llx\n",
                          lock, oscl, oscl->ols_flags);

        return 0;
}

/**
 * Finds an existing lock covering given index and optionally different from a
 * given \a except lock.
 */
struct ldlm_lock *osc_dlmlock_at_pgoff(const struct lu_env *env,
                                       struct osc_object *obj, pgoff_t index,
                                       int pending, int canceling)
{
        struct osc_thread_info *info = osc_env_info(env);
        struct ldlm_res_id *resname = &info->oti_resname;
        ldlm_policy_data_t *policy  = &info->oti_policy;
        struct lustre_handle lockh;
        struct ldlm_lock *lock = NULL;
        enum ldlm_mode mode;
        __u64 flags;

        ostid_build_res_name(&obj->oo_oinfo->loi_oi, resname);
        osc_index2policy(policy, osc2cl(obj), index, index);
        policy->l_extent.gid = LDLM_GID_ANY;

        flags = LDLM_FL_BLOCK_GRANTED | LDLM_FL_TEST_LOCK;
        if (pending)
                flags |= LDLM_FL_CBPENDING;
        /*
         * It is fine to match any group lock since there could be only one
         * with a uniq gid and it conflicts with all other lock modes too
         */
again:
        mode = ldlm_lock_match(osc_export(obj)->exp_obd->obd_namespace,
                               flags, resname, LDLM_EXTENT, policy,
                               LCK_PR | LCK_PW | LCK_GROUP, &lockh, canceling);
        if (mode != 0) {
                lock = ldlm_handle2lock(&lockh);
                /* RACE: the lock is cancelled so let's try again */
                if (unlikely(!lock))
                        goto again;
        }
        return lock;
}

/** @} osc */