Jiufei Xue 53cfdc10a9 blk-throttle: fix null pointer dereference while throttling writeback IOs
A null pointer dereference can occur when blkcg is removed manually
with writeback IOs inflight. This is caused by the following case:

Writeback kworker submit the bio and set bio->bi_cg_private to tg
in blk_throtl_assoc_bio.
Then we remove the block cgroup manually, the blkg and tg would be
freed if there is no request inflight.
When the submitted bio come back, blk_throtl_bio_endio() fetch the tg
which was already freed.

Fix this by increasing the refcount of blkg in funcion
blk_throtl_assoc_bio() so that the blkg will not be freed until the
bio_endio called.

Reviewed-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jiufei Xue <jiufei.xjf@alibaba-inc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-10-10 13:09:34 -06:00
..
2017-10-01 01:26:21 -06:00
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