staging/lustre/llite: Make sure ft_flags is valid

In ll_fault0, the 'fault' struct is mostly cleared before the call to
cl_io_loop, but ft_flags is not reset. It is ordinarily set by
the call to filemap_fault in vvp_io_kernel_fault, but if Lustre
returns before calling filemap_fault, it still has the old value of
ft_flags.

ll_fault0 will then consume the ft_flags field. If it has the
VM_FAULT_RETRY bit set, it will be used as ll_fault0() and
ll_fault()'s return value.

This is a problem when VM_FAULT_RETRY is in ft_flags:
When fault/filemap_fault return with that flag set, they have already
released the mmap semaphore, and do_page_fault does not need to
release it.
Incorrectly returning this flag from ll_fault means mmap_sem
is not upped in the kernel's do_page_fault().

In addition to clearing ft_flags, this patch does not use it unless
it is valid.  It's potentially misleading to return ft_flags in
"fault_ret" if ft_flags has not been set by filemap_fault.

This adds clarity, but does not change the current behavior:
When not valid, ft_flags is replaced by fault_ret, which is zero,
as is ft_flags when not set by filemap_fault.

Signed-off-by: Patrick Farrell <paf@cray.com>
Reviewed-on: http://review.whamcloud.com/10956
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5291
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/lustre/lustre/llite/llite_internal.h b/drivers/staging/lustre/lustre/llite/llite_internal.h
index 634ffa645e065a65dded26ed39075a000a1f339f..684405e26b5841076c3f491f492f83e9f7a9aa30 100644 (file)
--- a/drivers/staging/lustre/lustre/llite/llite_internal.h
+++ b/drivers/staging/lustre/lustre/llite/llite_internal.h
@@ -894,6 +894,10 @@ struct vvp_io {
                                 * fault API used bitflags for return code.
                                 */
                                unsigned int    ft_flags;
+                               /**
+                                * check that flags are from filemap_fault
+                                */
+                               bool            ft_flags_valid;
                        } fault;
                } fault;
        } u;

diff --git a/drivers/staging/lustre/lustre/llite/llite_mmap.c b/drivers/staging/lustre/lustre/llite/llite_mmap.c
index 7dae610f5c86e70ba4d27580aa4731d8264df2b1..59166481e1a27b50acf284bcff88883419710e52 100644 (file)
--- a/drivers/staging/lustre/lustre/llite/llite_mmap.c
+++ b/drivers/staging/lustre/lustre/llite/llite_mmap.c
@@ -310,10 +310,16 @@ static int ll_fault0(struct vm_area_struct *vma, struct vm_fault *vmf)
                vio->u.fault.ft_vma       = vma;
                vio->u.fault.ft_vmpage    = NULL;
                vio->u.fault.fault.ft_vmf = vmf;
+               vio->u.fault.fault.ft_flags = 0;
+               vio->u.fault.fault.ft_flags_valid = 0;
 
                result = cl_io_loop(env, io);
 
-               fault_ret = vio->u.fault.fault.ft_flags;
+               /* ft_flags are only valid if we reached
+                * the call to filemap_fault */
+               if (vio->u.fault.fault.ft_flags_valid)
+                       fault_ret = vio->u.fault.fault.ft_flags;
+
                vmpage = vio->u.fault.ft_vmpage;
                if (result != 0 && vmpage != NULL) {
                        page_cache_release(vmpage);

diff --git a/drivers/staging/lustre/lustre/llite/vvp_io.c b/drivers/staging/lustre/lustre/llite/vvp_io.c
index a4117d6a3866217d807a12dd857e1329a99047c2..fd248745cbffac33d3e6d256974fc9fadebc0e7a 100644 (file)
--- a/drivers/staging/lustre/lustre/llite/vvp_io.c
+++ b/drivers/staging/lustre/lustre/llite/vvp_io.c
@@ -615,6 +615,7 @@ static int vvp_io_kernel_fault(struct vvp_fault_io *cfio)
        struct vm_fault *vmf = cfio->fault.ft_vmf;
 
        cfio->fault.ft_flags = filemap_fault(cfio->ft_vma, vmf);
+       cfio->fault.ft_flags_valid = 1;
 
        if (vmf->page) {
                CDEBUG(D_PAGE,