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Subject[PATCH 5/9] block: ioc_task_link() can't fail
Date
ioc_task_link() is used to share %current's ioc on clone.  If
%current->is_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.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
---
include/linux/iocontext.h | 16 +++++-----------
kernel/fork.c | 5 ++---
2 files changed, 7 insertions(+), 14 deletions(-)
diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index 1a30180..81a8870 100644
--- 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 b77fd55..a1b6327 100644
--- 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))
--
1.7.7.3


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