block: ioc_task_link() can't fail

ioc_task_link() is used to share %current's ioc on clone.  If
%current->io_context is set, %current is guaranteed to have refcount
on the ioc and, thus, ioc_task_link() can't fail.

Replace error checking in ioc_task_link() with WARN_ON_ONCE() and make
it just increment refcount and nr_tasks.

-v2: Description typo fix (Vivek).

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index 1a30180630343dabd49aa886fc7621964912afdf..81a8870ac224d8eac76f97a25665bfa6720f86de 100644 (file)
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -120,18 +120,12 @@ struct io_context {
        struct work_struct release_work;
 };
 
-static inline struct io_context *ioc_task_link(struct io_context *ioc)
+static inline void ioc_task_link(struct io_context *ioc)
 {
-       /*
-        * if ref count is zero, don't allow sharing (ioc is going away, it's
-        * a race).
-        */
-       if (ioc && atomic_long_inc_not_zero(&ioc->refcount)) {
-               atomic_inc(&ioc->nr_tasks);
-               return ioc;
-       }
-
-       return NULL;
+       WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0);
+       WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0);
+       atomic_long_inc(&ioc->refcount);
+       atomic_inc(&ioc->nr_tasks);
 }
 
 struct task_struct;

diff --git a/kernel/fork.c b/kernel/fork.c
index b77fd559c78e6bbe6f92a2dfa26542a0714db083..a1b632713e4398eb4bd02a541f0b65599c3e509d 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -901,9 +901,8 @@ static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
         * Share io context with parent, if CLONE_IO is set
         */
        if (clone_flags & CLONE_IO) {
-               tsk->io_context = ioc_task_link(ioc);
-               if (unlikely(!tsk->io_context))
-                       return -ENOMEM;
+               ioc_task_link(ioc);
+               tsk->io_context = ioc;
        } else if (ioprio_valid(ioc->ioprio)) {
                new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
                if (unlikely(!new_ioc))