[PATCH] block: fix ioc leak in put_io_context

[Xiaotian Feng <xtfeng@gmail.com>]

When put_io_context is called, if ioc->icq_list is empty and refcount
is 1, kernel will not free the ioc.

This is caught by following kmemleak:

unreferenced object 0xffff880036349fe0 (size 216):
  comm "sh", pid 2137, jiffies 4294931140 (age 290579.412s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    01 00 01 00 ad 4e ad de ff ff ff ff 00 00 00 00  .....N..........
  backtrace:
    [<ffffffff8169f926>] kmemleak_alloc+0x26/0x50
    [<ffffffff81195a9c>] kmem_cache_alloc_node+0x1cc/0x2a0
    [<ffffffff81356b67>] create_io_context_slowpath+0x27/0x130
    [<ffffffff81356d2b>] get_task_io_context+0xbb/0xf0
    [<ffffffff81055f0e>] copy_process+0x188e/0x18b0
    [<ffffffff8105609b>] do_fork+0x11b/0x420
    [<ffffffff810247f8>] sys_clone+0x28/0x30
    [<ffffffff816d3373>] stub_clone+0x13/0x20
    [<ffffffffffffffff>] 0xffffffffffffffff

ioc->release_work() should be used even if ioc->icq_list is empty.

Signed-off-by: Xiaotian Feng <dannyfeng@tencent.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk> 
---
 block/blk-ioc.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 8b782a6..d74a8ce 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -157,8 +157,7 @@ void put_io_context(struct io_context *ioc)
 	 */
 	if (atomic_long_dec_and_test(&ioc->refcount)) {
 		spin_lock_irqsave(&ioc->lock, flags);
-		if (!hlist_empty(&ioc->icq_list))
-			schedule_work(&ioc->release_work);
+		schedule_work(&ioc->release_work);
 		spin_unlock_irqrestore(&ioc->lock, flags);
 	}
 }
-- 
1.7.5.4