From: Jiufei Xue <jiufei.xjf@xxxxxxxxxxxxxxx>
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 <jiufei.xjf@xxxxxxxxxxxxxxx>
---
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
--
1.9.4
