block: fix ioc leak in put_io_context

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 should be freed if ioc->icq_list is empty.
Signed-off-by: Xiaotian Feng <dannyfeng@tencent.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 6 insertions, 0 deletions

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 92bf55540d87..fb95dd2f889a 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -130,6 +130,7 @@ static void ioc_release_fn(struct work_struct *work)
 void put_io_context(struct io_context *ioc)
 {
         unsigned long flags;
+        bool free_ioc = false;
 
         if (ioc == NULL)
                 return;
@@ -144,8 +145,13 @@ void put_io_context(struct io_context *ioc)
                 spin_lock_irqsave(&ioc->lock, flags);
                 if (!hlist_empty(&ioc->icq_list))
                         schedule_work(&ioc->release_work);
+                else
+                        free_ioc = true;
                 spin_unlock_irqrestore(&ioc->lock, flags);
         }
+
+        if (free_ioc)
+                kmem_cache_free(iocontext_cachep, ioc);
 }
 EXPORT_SYMBOL(put_io_context);