On 10/10/2017 01:05 PM, Shaohua Li wrote: > On Tue, Oct 10, 2017 at 12:48:38PM -0600, Jens Axboe wrote: >> On 10/10/2017 12:13 PM, Shaohua Li wrote: >>> On Tue, Oct 10, 2017 at 11:13:32AM +0800, xuejiufei wrote: >>>> From: Jiufei Xue <[email protected]> >>>> >>>> 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. >>>> >>>> Signed-off-by: Jiufei Xue <[email protected]> >>>> --- >>>> block/blk-throttle.c | 12 ++++++++++-- >>>> 1 file changed, 10 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/block/blk-throttle.c b/block/blk-throttle.c >>>> index 17816a0..d80c3f0 100644 >>>> --- a/block/blk-throttle.c >>>> +++ b/block/blk-throttle.c >>>> @@ -2112,8 +2112,12 @@ static inline void >>>> throtl_update_latency_buckets(struct throtl_data *td) >>>> static void blk_throtl_assoc_bio(struct throtl_grp *tg, struct bio *bio) >>>> { >>>> #ifdef CONFIG_BLK_DEV_THROTTLING_LOW >>>> - if (bio->bi_css) >>>> + if (bio->bi_css) { >>>> + if (bio->bi_cg_private) >>>> + blkg_put(tg_to_blkg(bio->bi_cg_private)); >>>> bio->bi_cg_private = tg; >>>> + blkg_get(tg_to_blkg(tg)); >>>> + } >>>> blk_stat_set_issue(&bio->bi_issue_stat, bio_sectors(bio)); >>>> #endif >>>> } >>>> @@ -2283,8 +2287,10 @@ void blk_throtl_bio_endio(struct bio *bio) >>>> >>>> start_time = blk_stat_time(&bio->bi_issue_stat) >> 10; >>>> finish_time = __blk_stat_time(finish_time_ns) >> 10; >>>> - if (!start_time || finish_time <= start_time) >>>> + if (!start_time || finish_time <= start_time) { >>>> + blkg_put(tg_to_blkg(tg)); >>>> return; >>>> + } >>>> >>>> lat = finish_time - start_time; >>>> /* this is only for bio based driver */ >>>> @@ -2314,6 +2320,8 @@ void blk_throtl_bio_endio(struct bio *bio) >>>> tg->bio_cnt /= 2; >>>> tg->bad_bio_cnt /= 2; >>>> } >>>> + >>>> + blkg_put(tg_to_blkg(tg)); >>>> } >>>> #endif >>> >>> Reviewed-by: Shaohua Li <[email protected]> >> >> I was going to queue this up for 4.15, but was wondering if there's a >> strong reason to include it for 4.14 instead? > > Either is ok to me, this isn't easy to trigger, but on the other hand it's > quite safe.
OK, let's just stick with 4.15 then. -- Jens Axboe
