WARNING: at block/blk-ioc.c:234 exit_io_context+0x40/0x92()

Hi,

Commit 6e736be7 ("block: make ioc get/put interface more conventional and fix race on alloction") added a warning to exit_io_context() which is triggered by failed clone() syscall.

Here is the warning;

[  294.417656] ------------[ cut here ]------------
[  294.418897] WARNING: at block/blk-ioc.c:234 exit_io_context+0x40/0x92()
[  294.420538] Pid: 17090, comm: trinity Not tainted 3.2.0-rc6-next-20111222-sasha-dirty #77
[  294.422231] Call Trace:
[  294.422701]  [<ffffffff8181a7a2>] ? exit_io_context+0x40/0x92
[  294.423842]  [<ffffffff8181a7a2>] ? exit_io_context+0x40/0x92
[  294.424919]  [<ffffffff810b69a3>] warn_slowpath_common+0x8f/0xb2
[  294.426036]  [<ffffffff810b6a77>] warn_slowpath_null+0x18/0x1a
[  294.427114]  [<ffffffff8181a7a2>] exit_io_context+0x40/0x92
[  294.428121]  [<ffffffff810b58c9>] copy_process+0x126f/0x1453
[  294.429131]  [<ffffffff810891f6>] ? do_page_fault+0x48a/0x4a4
[  294.430162]  [<ffffffff810b5c1b>] do_fork+0x120/0x3e9
[  294.431160]  [<ffffffff82421b57>] ? mutex_unlock+0x9/0xb
[  294.432150]  [<ffffffff8110f999>] ? lock_release_holdtime+0xc6/0xd4
[  294.433296]  [<ffffffff82424bdd>] ? retint_swapgs+0x13/0x1b
[  294.434336]  [<ffffffff8106242f>] sys_clone+0x26/0x28
[  294.435277]  [<ffffffff82425803>] stub_clone+0x13/0x20
[  294.436230]  [<ffffffff82425479>] ? system_call_fastpath+0x16/0x1b
[  294.437381] ---[ end trace a2e4eb670b375238 ]---

Sasha.

6e736be7 "block: make ioc get/put interface more conventional and fix race on alloction" added WARN_ON_ONCE() in exit_io_context() which triggers if !PF_EXITING. All tasks hitting exit_io_context() from task exit should have PF_EXITING set but task struct tearing down after fork failure calls into the function without PF_EXITING, triggering the condition.

  WARNING: at block/blk-ioc.c:234 exit_io_context+0x40/0x92()
  Pid: 17090, comm: trinity Not tainted 3.2.0-rc6-next-20111222-sasha-dirty #77
  Call Trace:
   [<ffffffff810b69a3>] warn_slowpath_common+0x8f/0xb2
   [<ffffffff810b6a77>] warn_slowpath_null+0x18/0x1a
   [<ffffffff8181a7a2>] exit_io_context+0x40/0x92
   [<ffffffff810b58c9>] copy_process+0x126f/0x1453
   [<ffffffff810b5c1b>] do_fork+0x120/0x3e9
   [<ffffffff8106242f>] sys_clone+0x26/0x28
   [<ffffffff82425803>] stub_clone+0x13/0x20
  ---[ end trace a2e4eb670b375238 ]---

---
Heh, sorry about that. Forgot about fork failure path. Just removing the WARN_ON_ONCE() should be enough. Thanks for reporting the problem.

 block/blk-ioc.c |    3 ---
 1 file changed, 3 deletions(-)

index 33fae7d..27a06e0 100644
@@ -230,9 +230,6 @@ void exit_io_context(struct task_struct *task)
 {
 	struct io_context *ioc;
 
-	/* PF_EXITING prevents new io_context from being attached to @task */
-	WARN_ON_ONCE(!(current->flags & PF_EXITING));
-
 	task_lock(task);
 	ioc = task->io_context;
 	task->io_context = NULL;

Thanks, applied.

Jens Axboe