blk-throttle: fix NULL pointer dereference in throtl_schedule_pending_timer
authorJoseph Qi <qijiang.qj@alibaba-inc.com>
Wed, 7 Jun 2017 03:36:14 +0000 (11:36 +0800)
committerJens Axboe <axboe@fb.com>
Wed, 7 Jun 2017 14:11:24 +0000 (08:11 -0600)
commita41b816c174409417d91b4ceef0145c9f0bef67c
tree82b3b4311eb770dfd22e25fb9e67cff08d885c4f
parent9bd2bbc01d17ddd567cc0f81f77fe1163e497462
blk-throttle: fix NULL pointer dereference in throtl_schedule_pending_timer

I have encountered a NULL pointer dereference in
throtl_schedule_pending_timer:
  [  413.735396] BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
  [  413.735535] IP: [<ffffffff812ebbbf>] throtl_schedule_pending_timer+0x3f/0x210
  [  413.735643] PGD 22c8cf067 PUD 22cb34067 PMD 0
  [  413.735713] Oops: 0000 [#1] SMP
  ......

This is caused by the following case:
  blk_throtl_bio
    throtl_schedule_next_dispatch  <= sq is top level one without parent
      throtl_schedule_pending_timer
        sq_to_tg(sq)->td->throtl_slice  <= sq_to_tg(sq) returns NULL

Fix it by using sq_to_td instead of sq_to_tg(sq)->td, which will always
return a valid td.

Fixes: 297e3d854784 ("blk-throttle: make throtl_slice tunable")
Signed-off-by: Joseph Qi <qijiang.qj@alibaba-inc.com>
Reviewed-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
block/blk-throttle.c