| Message ID | 20190925122025.31246-1-yuyufen@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v4] block: fix null pointer dereference in blk_mq_rq_timed_out() | expand |
On 9/25/19 2:20 PM, Yufen Yu wrote: > diff --git a/block/blk.h b/block/blk.h > index ed347f7a97b1..de258e7b9db8 100644 > --- a/block/blk.h > +++ b/block/blk.h > @@ -30,6 +30,7 @@ struct blk_flush_queue { > */ > struct request *orig_rq; > spinlock_t mq_flush_lock; > + blk_status_t rq_status; > }; Patch looks fine to me, but you should move rq_status to after the flush_running_idx member of struct blk_flush_queue, since then it'll fill a padding hole instead of adding new ones.
On 2019/9/26 18:04, Jens Axboe wrote: > On 9/25/19 2:20 PM, Yufen Yu wrote: >> diff --git a/block/blk.h b/block/blk.h >> index ed347f7a97b1..de258e7b9db8 100644 >> --- a/block/blk.h >> +++ b/block/blk.h >> @@ -30,6 +30,7 @@ struct blk_flush_queue { >> */ >> struct request *orig_rq; >> spinlock_t mq_flush_lock; >> + blk_status_t rq_status; >> }; > Patch looks fine to me, but you should move rq_status to after the > flush_running_idx member of struct blk_flush_queue, since then it'll > fill a padding hole instead of adding new ones. > Thanks for you good suggestion. Thanks, Yufen
Yufen Yu <yuyufen@huawei.com> 于2019年9月26日周四 上午11:30写道： > > We got a null pointer deference BUG_ON in blk_mq_rq_timed_out() > as following: > > [ 108.825472] BUG: kernel NULL pointer dereference, address: 0000000000000040 > [ 108.827059] PGD 0 P4D 0 > [ 108.827313] Oops: 0000 [#1] SMP PTI > [ 108.827657] CPU: 6 PID: 198 Comm: kworker/6:1H Not tainted 5.3.0-rc8+ #431 > [ 108.829503] Workqueue: kblockd blk_mq_timeout_work > [ 108.829913] RIP: 0010:blk_mq_check_expired+0x258/0x330 > [ 108.838191] Call Trace: > [ 108.838406] bt_iter+0x74/0x80 > [ 108.838665] blk_mq_queue_tag_busy_iter+0x204/0x450 > [ 108.839074] ? __switch_to_asm+0x34/0x70 > [ 108.839405] ? blk_mq_stop_hw_queue+0x40/0x40 > [ 108.839823] ? blk_mq_stop_hw_queue+0x40/0x40 > [ 108.840273] ? syscall_return_via_sysret+0xf/0x7f > [ 108.840732] blk_mq_timeout_work+0x74/0x200 > [ 108.841151] process_one_work+0x297/0x680 > [ 108.841550] worker_thread+0x29c/0x6f0 > [ 108.841926] ? rescuer_thread+0x580/0x580 > [ 108.842344] kthread+0x16a/0x1a0 > [ 108.842666] ? kthread_flush_work+0x170/0x170 > [ 108.843100] ret_from_fork+0x35/0x40 > > The bug is caused by the race between timeout handle and completion for > flush request. > > When timeout handle function blk_mq_rq_timed_out() try to read > 'req->q->mq_ops', the 'req' have completed and reinitiated by next > flush request, which would call blk_rq_init() to clear 'req' as 0. > > After commit 12f5b93145 ("blk-mq: Remove generation seqeunce"), > normal requests lifetime are protected by refcount. Until 'rq->ref' > drop to zero, the request can really be free. Thus, these requests > cannot been reused before timeout handle finish. > > However, flush request has defined .end_io and rq->end_io() is still > called even if 'rq->ref' doesn't drop to zero. After that, the 'flush_rq' > can be reused by the next flush request handle, resulting in null > pointer deference BUG ON. > > We fix this problem by covering flush request with 'rq->ref'. > If the refcount is not zero, flush_end_io() return and wait the > last holder recall it. To record the request status, we add a new > entry 'rq_status', which will be used in flush_end_io(). > > Cc: Ming Lei <ming.lei@redhat.com> > Cc: Christoph Hellwig <hch@infradead.org> > Cc: Keith Busch <keith.busch@intel.com> > Cc: Bart Van Assche <bvanassche@acm.org> > Cc: stable@vger.kernel.org # v4.18+ > Signed-off-by: Yufen Yu <yuyufen@huawei.com> > Hi Yufen, Can you share your reproducer, I think the bug was there for long time, we hit it in kernel 4.4. We also need to fix it for older LTS kernel. Do you have an idea, how should we fix it for older LTS kernel? Regards, Jack Wang
On 2019/10/9 16:26, Jack Wang wrote: > >> We got a null pointer deference BUG_ON in blk_mq_rq_timed_out() >> as following: >> >> [ 108.825472] BUG: kernel NULL pointer dereference, address: 0000000000000040 >> [ 108.827059] PGD 0 P4D 0 >> [ 108.827313] Oops: 0000 [#1] SMP PTI >> [ 108.827657] CPU: 6 PID: 198 Comm: kworker/6:1H Not tainted 5.3.0-rc8+ #431 >> [ 108.829503] Workqueue: kblockd blk_mq_timeout_work >> [ 108.829913] RIP: 0010:blk_mq_check_expired+0x258/0x330 >> [ 108.838191] Call Trace: >> [ 108.838406] bt_iter+0x74/0x80 >> [ 108.838665] blk_mq_queue_tag_busy_iter+0x204/0x450 >> [ 108.839074] ? __switch_to_asm+0x34/0x70 >> [ 108.839405] ? blk_mq_stop_hw_queue+0x40/0x40 >> [ 108.839823] ? blk_mq_stop_hw_queue+0x40/0x40 >> [ 108.840273] ? syscall_return_via_sysret+0xf/0x7f >> [ 108.840732] blk_mq_timeout_work+0x74/0x200 >> [ 108.841151] process_one_work+0x297/0x680 >> [ 108.841550] worker_thread+0x29c/0x6f0 >> [ 108.841926] ? rescuer_thread+0x580/0x580 >> [ 108.842344] kthread+0x16a/0x1a0 >> [ 108.842666] ? kthread_flush_work+0x170/0x170 >> [ 108.843100] ret_from_fork+0x35/0x40 >> >> The bug is caused by the race between timeout handle and completion for >> flush request. >> >> When timeout handle function blk_mq_rq_timed_out() try to read >> 'req->q->mq_ops', the 'req' have completed and reinitiated by next >> flush request, which would call blk_rq_init() to clear 'req' as 0. >> >> After commit 12f5b93145 ("blk-mq: Remove generation seqeunce"), >> normal requests lifetime are protected by refcount. Until 'rq->ref' >> drop to zero, the request can really be free. Thus, these requests >> cannot been reused before timeout handle finish. >> >> However, flush request has defined .end_io and rq->end_io() is still >> called even if 'rq->ref' doesn't drop to zero. After that, the 'flush_rq' >> can be reused by the next flush request handle, resulting in null >> pointer deference BUG ON. >> >> We fix this problem by covering flush request with 'rq->ref'. >> If the refcount is not zero, flush_end_io() return and wait the >> last holder recall it. To record the request status, we add a new >> entry 'rq_status', which will be used in flush_end_io(). >> >> Cc: Ming Lei <ming.lei@redhat.com> >> Cc: Christoph Hellwig <hch@infradead.org> >> Cc: Keith Busch <keith.busch@intel.com> >> Cc: Bart Van Assche <bvanassche@acm.org> >> Cc: stable@vger.kernel.org # v4.18+ >> Signed-off-by: Yufen Yu <yuyufen@huawei.com> >> > Hi Yufen, > > Can you share your reproducer, I think the bug was there for long > time, we hit it in kernel 4.4. > We also need to fix it for older LTS kernel. > > Do you have an idea, how should we fix it for older LTS kernel? > I have reproduced the bug by increasing delay after doing memset() in blk_rq_init() and before calling blk_mq_rq_timed_out() in blk_mq_check_expired(). To make sure the request will be timeout, I have also increase delay for flush request after blk_mq_start_request() in virtio_queue_rq() for my virtio disk. Then, we just issue a flush request for the disk by fio. The BUG_ON will be triggered. For LTS 4.4 or older kernel, the race between timeout handle and completion for normal request have not yet resolved. So, IMO, we should fix the bug first by merging commit 12f5b93145 ("blk-mq: Remove generation seqeunce") and its related patches. After that, this patch can also be merged. Thanks, Yufen
diff --git a/block/blk-flush.c b/block/blk-flush.c index aedd9320e605..1eec9cbe5a0a 100644 --- a/block/blk-flush.c +++ b/block/blk-flush.c @@ -214,6 +214,16 @@ static void flush_end_io(struct request *flush_rq, blk_status_t error) /* release the tag's ownership to the req cloned from */ spin_lock_irqsave(&fq->mq_flush_lock, flags); + + if (!refcount_dec_and_test(&flush_rq->ref)) { + fq->rq_status = error; + spin_unlock_irqrestore(&fq->mq_flush_lock, flags); + return; + } + + if (fq->rq_status != BLK_STS_OK) + error = fq->rq_status; + hctx = flush_rq->mq_hctx; if (!q->elevator) { blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq); diff --git a/block/blk-mq.c b/block/blk-mq.c index 20a49be536b5..e04fa9ab5574 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -912,7 +912,10 @@ static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx, */ if (blk_mq_req_expired(rq, next)) blk_mq_rq_timed_out(rq, reserved); - if (refcount_dec_and_test(&rq->ref)) + + if (is_flush_rq(rq, hctx)) + rq->end_io(rq, 0); + else if (refcount_dec_and_test(&rq->ref)) __blk_mq_free_request(rq); return true; diff --git a/block/blk.h b/block/blk.h index ed347f7a97b1..de258e7b9db8 100644 --- a/block/blk.h +++ b/block/blk.h @@ -30,6 +30,7 @@ struct blk_flush_queue { */ struct request *orig_rq; spinlock_t mq_flush_lock; + blk_status_t rq_status; }; extern struct kmem_cache *blk_requestq_cachep; @@ -47,6 +48,12 @@ static inline void __blk_get_queue(struct request_queue *q) kobject_get(&q->kobj); } +static inline bool +is_flush_rq(struct request *req, struct blk_mq_hw_ctx *hctx) +{ + return hctx->fq->flush_rq == req; +} + struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q, int node, int cmd_size, gfp_t flags); void blk_free_flush_queue(struct blk_flush_queue *q);
We got a null pointer deference BUG_ON in blk_mq_rq_timed_out() as following: [ 108.825472] BUG: kernel NULL pointer dereference, address: 0000000000000040 [ 108.827059] PGD 0 P4D 0 [ 108.827313] Oops: 0000 [#1] SMP PTI [ 108.827657] CPU: 6 PID: 198 Comm: kworker/6:1H Not tainted 5.3.0-rc8+ #431 [ 108.829503] Workqueue: kblockd blk_mq_timeout_work [ 108.829913] RIP: 0010:blk_mq_check_expired+0x258/0x330 [ 108.838191] Call Trace: [ 108.838406] bt_iter+0x74/0x80 [ 108.838665] blk_mq_queue_tag_busy_iter+0x204/0x450 [ 108.839074] ? __switch_to_asm+0x34/0x70 [ 108.839405] ? blk_mq_stop_hw_queue+0x40/0x40 [ 108.839823] ? blk_mq_stop_hw_queue+0x40/0x40 [ 108.840273] ? syscall_return_via_sysret+0xf/0x7f [ 108.840732] blk_mq_timeout_work+0x74/0x200 [ 108.841151] process_one_work+0x297/0x680 [ 108.841550] worker_thread+0x29c/0x6f0 [ 108.841926] ? rescuer_thread+0x580/0x580 [ 108.842344] kthread+0x16a/0x1a0 [ 108.842666] ? kthread_flush_work+0x170/0x170 [ 108.843100] ret_from_fork+0x35/0x40 The bug is caused by the race between timeout handle and completion for flush request. When timeout handle function blk_mq_rq_timed_out() try to read 'req->q->mq_ops', the 'req' have completed and reinitiated by next flush request, which would call blk_rq_init() to clear 'req' as 0. After commit 12f5b93145 ("blk-mq: Remove generation seqeunce"), normal requests lifetime are protected by refcount. Until 'rq->ref' drop to zero, the request can really be free. Thus, these requests cannot been reused before timeout handle finish. However, flush request has defined .end_io and rq->end_io() is still called even if 'rq->ref' doesn't drop to zero. After that, the 'flush_rq' can be reused by the next flush request handle, resulting in null pointer deference BUG ON. We fix this problem by covering flush request with 'rq->ref'. If the refcount is not zero, flush_end_io() return and wait the last holder recall it. To record the request status, we add a new entry 'rq_status', which will be used in flush_end_io(). Cc: Ming Lei <ming.lei@redhat.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Keith Busch <keith.busch@intel.com> Cc: Bart Van Assche <bvanassche@acm.org> Cc: stable@vger.kernel.org # v4.18+ Signed-off-by: Yufen Yu <yuyufen@huawei.com> ------- v2: - move rq_status from struct request to struct blk_flush_queue v3: - remove unnecessary '{}' pair. v4: - let spinlock to protect 'fq->rq_status' --- block/blk-flush.c | 10 ++++++++++ block/blk-mq.c | 5 ++++- block/blk.h | 7 +++++++ 3 files changed, 21 insertions(+), 1 deletion(-)