* [PATCH 0/2] Fix a race condition triggered by submit_bio()
@ 2019-07-30 18:17 Bart Van Assche
2019-07-30 18:17 ` [PATCH 1/2] block: Verify whether blk_queue_enter() is used when necessary Bart Van Assche
2019-07-30 18:17 ` [PATCH 2/2] block: Fix a race condition in submit_bio() Bart Van Assche
0 siblings, 2 replies; 8+ messages in thread
From: Bart Van Assche @ 2019-07-30 18:17 UTC (permalink / raw)
To: Jens Axboe; +Cc: linux-block, Christoph Hellwig, Bart Van Assche
Hi Jens,
One of the consequences of the switch to blk-mq is that generic_make_request()
calls, a function called by submit_bio(), must be protected by a
blk_queue_enter() / blk_queue_exit() pair to avoid that the block-cgroup
functions called by generic_make_request() trigger a race condition. This patch
series makes the kernel report a warning if that race condition is hit and also
adds the necessary protection in submit_bio(). Please consider these patches
for kernel v5.4.
Thanks,
Bart.
Bart Van Assche (2):
block: Verify whether blk_queue_enter() is used when necessary
block: Fix a race condition in submit_bio()
block/blk-cgroup.c | 2 ++
block/blk-core.c | 34 +++++++++++++++++++++++++++++++++-
include/linux/blk-cgroup.h | 2 ++
include/linux/blkdev.h | 8 ++++++++
4 files changed, 45 insertions(+), 1 deletion(-)
--
2.22.0.709.g102302147b-goog
^ permalink raw reply [flat|nested] 8+ messages in thread
* [PATCH 1/2] block: Verify whether blk_queue_enter() is used when necessary
2019-07-30 18:17 [PATCH 0/2] Fix a race condition triggered by submit_bio() Bart Van Assche
@ 2019-07-30 18:17 ` Bart Van Assche
2019-07-31 1:46 ` Ming Lei
2019-07-30 18:17 ` [PATCH 2/2] block: Fix a race condition in submit_bio() Bart Van Assche
1 sibling, 1 reply; 8+ messages in thread
From: Bart Van Assche @ 2019-07-30 18:17 UTC (permalink / raw)
To: Jens Axboe
Cc: linux-block, Christoph Hellwig, Bart Van Assche, Tejun Heo,
Ming Lei, Hannes Reinecke, Johannes Thumshirn, Alexandru Moise,
Joseph Qi
It is required to protect blkg_lookup() calls with a blk_queue_enter() /
blk_queue_exit() pair. Since it is nontrivial to verify whether this is
the case, verify this at runtime. Only perform this verification if
CONFIG_LOCKDEP=y to avoid that unnecessary runtime overhead is added.
Note: using lock_acquire()/lock_release() to verify whether blkg_lookup()
is protected correctly is not possible since lock_acquire() and
lock_release() must be called from the same task and since
blk_queue_enter() and blk_queue_exit() can be called from different
tasks.
Suggested-by: Tejun Heo <tj@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Alexandru Moise <00moses.alexander00@gmail.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
block/blk-cgroup.c | 2 ++
block/blk-core.c | 21 +++++++++++++++++++++
include/linux/blk-cgroup.h | 2 ++
include/linux/blkdev.h | 8 ++++++++
4 files changed, 33 insertions(+)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 24ed26957367..04b6e962eefb 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -196,6 +196,8 @@ struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
{
struct blkcg_gq *blkg;
+ WARN_ON_ONCE(!blk_entered_queue(q));
+
/*
* Hint didn't match. Look up from the radix tree. Note that the
* hint can only be updated under queue_lock as otherwise @blkg
diff --git a/block/blk-core.c b/block/blk-core.c
index 5878504a29af..ff27c3080348 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -389,6 +389,25 @@ struct request_queue *blk_alloc_queue(gfp_t gfp_mask)
}
EXPORT_SYMBOL(blk_alloc_queue);
+#ifdef CONFIG_PROVE_LOCKING
+/**
+ * blk_entered_queue() - whether or not it is safe to access cgroup information
+ * @q: request queue pointer
+ *
+ * In order to avoid races between accessing cgroup information and the cgroup
+ * information removal from inside __blk_release_queue(), any code that accesses
+ * cgroup information must be protected by a blk_queue_enter()/blk_queue_exit()
+ * pair or must be called after queue cleanup progressed to a stage in which
+ * only the cleanup code accesses the queue.
+ */
+bool blk_entered_queue(struct request_queue *q)
+{
+ return percpu_ref_is_dying(&q->q_usage_counter) ||
+ !percpu_ref_is_zero(&q->q_usage_counter);
+}
+EXPORT_SYMBOL(blk_entered_queue);
+#endif
+
/**
* blk_queue_enter() - try to increase q->q_usage_counter
* @q: request queue pointer
@@ -878,6 +897,8 @@ generic_make_request_checks(struct bio *bio)
goto end_io;
}
+ WARN_ON_ONCE(!blk_entered_queue(q));
+
/*
* For a REQ_NOWAIT based request, return -EOPNOTSUPP
* if queue is not a request based queue.
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 689a58231288..397df0719bda 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -358,6 +358,8 @@ static inline struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
{
struct blkcg_gq *blkg;
+ WARN_ON_ONCE(!blk_entered_queue(q));
+
if (blkcg == &blkcg_root)
return q->root_blkg;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 96a29a72fd4a..e57651888450 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -856,6 +856,14 @@ extern int sg_scsi_ioctl(struct request_queue *, struct gendisk *, fmode_t,
extern int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags);
extern void blk_queue_exit(struct request_queue *q);
+#ifdef CONFIG_PROVE_LOCKING
+extern bool blk_entered_queue(struct request_queue *q);
+#else
+static inline bool blk_entered_queue(struct request_queue *q)
+{
+ return true;
+}
+#endif
extern void blk_sync_queue(struct request_queue *q);
extern int blk_rq_map_user(struct request_queue *, struct request *,
struct rq_map_data *, void __user *, unsigned long,
--
2.22.0.709.g102302147b-goog
^ permalink raw reply related [flat|nested] 8+ messages in thread
* [PATCH 2/2] block: Fix a race condition in submit_bio()
2019-07-30 18:17 [PATCH 0/2] Fix a race condition triggered by submit_bio() Bart Van Assche
2019-07-30 18:17 ` [PATCH 1/2] block: Verify whether blk_queue_enter() is used when necessary Bart Van Assche
@ 2019-07-30 18:17 ` Bart Van Assche
2019-07-30 18:18 ` syzbot
2019-07-31 1:53 ` Ming Lei
1 sibling, 2 replies; 8+ messages in thread
From: Bart Van Assche @ 2019-07-30 18:17 UTC (permalink / raw)
To: Jens Axboe
Cc: linux-block, Christoph Hellwig, Bart Van Assche, Tejun Heo,
Ming Lei, Hannes Reinecke, Johannes Thumshirn, Alexandru Moise,
Joseph Qi, syzbot+ff9ab4a23afa7553
generic_make_request_checks() needs to be protected by a
blk_queue_enter() / blk_queue_exit() pair because it calls
blkcg_bio_issue_check() and because that last function calls
blkg_lookup().
This patch fixes https://syzkaller.appspot.com/bug?id=ff9ab4a23afa7553fb79f745a92be87ba4144508.
This patch also fixes the following kernel warning, triggered by
blktests:
WARNING: CPU: 5 PID: 10706 at block/blk-core.c:903 generic_make_request_checks+0x9c6/0xe60
RIP: 0010:generic_make_request_checks+0x9c6/0xe60
Call Trace:
generic_make_request+0x7a/0x5c0
submit_bio+0x92/0x280
mpage_readpages+0x2b1/0x300
blkdev_readpages+0x1d/0x20
read_pages+0xd9/0x2c0
__do_page_cache_readahead+0x2e0/0x310
force_page_cache_readahead+0xfb/0x170
page_cache_sync_readahead+0x28d/0x2a0
generic_file_read_iter+0xc13/0x1530
blkdev_read_iter+0x7d/0x90
new_sync_read+0x2c5/0x3d0
__vfs_read+0x7b/0x90
vfs_read+0xc6/0x1f0
ksys_read+0xc3/0x160
__x64_sys_read+0x43/0x50
do_syscall_64+0x71/0x270
entry_SYSCALL_64_after_hwframe+0x49/0xbe
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Alexandru Moise <00moses.alexander00@gmail.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Reported-by: syzbot+ff9ab4a23afa7553@syzkaller.appspotmail.com
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
block/blk-core.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index ff27c3080348..cd844c54e9f1 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1150,6 +1150,9 @@ EXPORT_SYMBOL_GPL(direct_make_request);
*/
blk_qc_t submit_bio(struct bio *bio)
{
+ struct request_queue *q = bio->bi_disk->queue;
+ blk_qc_t ret;
+
if (blkcg_punt_bio_submit(bio))
return BLK_QC_T_NONE;
@@ -1182,7 +1185,15 @@ blk_qc_t submit_bio(struct bio *bio)
}
}
- return generic_make_request(bio);
+ if (unlikely(blk_queue_enter(q, 0) < 0)) {
+ bio->bi_status = BLK_STS_IOERR;
+ bio->bi_end_io(bio);
+ return BLK_QC_T_NONE;
+ }
+ ret = generic_make_request(bio);
+ blk_queue_exit(q);
+
+ return ret;
}
EXPORT_SYMBOL(submit_bio);
--
2.22.0.709.g102302147b-goog
^ permalink raw reply related [flat|nested] 8+ messages in thread
* Re: [PATCH 2/2] block: Fix a race condition in submit_bio()
2019-07-30 18:17 ` [PATCH 2/2] block: Fix a race condition in submit_bio() Bart Van Assche
@ 2019-07-30 18:18 ` syzbot
2019-07-31 1:53 ` Ming Lei
1 sibling, 0 replies; 8+ messages in thread
From: syzbot @ 2019-07-30 18:18 UTC (permalink / raw)
To: Bart Van Assche
Cc: 00moses.alexander00, axboe, bvanassche, hare, hch, joseph.qi,
jthumshirn, linux-block, ming.lei, tj
> generic_make_request_checks() needs to be protected by a
> blk_queue_enter() / blk_queue_exit() pair because it calls
> blkcg_bio_issue_check() and because that last function calls
> blkg_lookup().
> This patch fixes
> https://syzkaller.appspot.com/bug?id=ff9ab4a23afa7553fb79f745a92be87ba4144508.
> This patch also fixes the following kernel warning, triggered by
> blktests:
> WARNING: CPU: 5 PID: 10706 at block/blk-core.c:903
> generic_make_request_checks+0x9c6/0xe60
> RIP: 0010:generic_make_request_checks+0x9c6/0xe60
> Call Trace:
> generic_make_request+0x7a/0x5c0
> submit_bio+0x92/0x280
> mpage_readpages+0x2b1/0x300
> blkdev_readpages+0x1d/0x20
> read_pages+0xd9/0x2c0
> __do_page_cache_readahead+0x2e0/0x310
> force_page_cache_readahead+0xfb/0x170
> page_cache_sync_readahead+0x28d/0x2a0
> generic_file_read_iter+0xc13/0x1530
> blkdev_read_iter+0x7d/0x90
> new_sync_read+0x2c5/0x3d0
> __vfs_read+0x7b/0x90
> vfs_read+0xc6/0x1f0
> ksys_read+0xc3/0x160
> __x64_sys_read+0x43/0x50
> do_syscall_64+0x71/0x270
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: Hannes Reinecke <hare@suse.com>
> Cc: Johannes Thumshirn <jthumshirn@suse.de>
> Cc: Alexandru Moise <00moses.alexander00@gmail.com>
> Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
> Reported-by: syzbot+ff9ab4a23afa7553@syzkaller.appspotmail.com
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
> block/blk-core.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
> diff --git a/block/blk-core.c b/block/blk-core.c
> index ff27c3080348..cd844c54e9f1 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1150,6 +1150,9 @@ EXPORT_SYMBOL_GPL(direct_make_request);
> */
> blk_qc_t submit_bio(struct bio *bio)
> {
> + struct request_queue *q = bio->bi_disk->queue;
> + blk_qc_t ret;
> +
> if (blkcg_punt_bio_submit(bio))
> return BLK_QC_T_NONE;
> @@ -1182,7 +1185,15 @@ blk_qc_t submit_bio(struct bio *bio)
> }
> }
> - return generic_make_request(bio);
> + if (unlikely(blk_queue_enter(q, 0) < 0)) {
> + bio->bi_status = BLK_STS_IOERR;
> + bio->bi_end_io(bio);
> + return BLK_QC_T_NONE;
> + }
> + ret = generic_make_request(bio);
> + blk_queue_exit(q);
> +
> + return ret;
> }
> EXPORT_SYMBOL(submit_bio);
> --
> 2.22.0.709.g102302147b-goog
I see the command but can't find the corresponding bug.
The email is sent to syzbot+HASH@syzkaller.appspotmail.com address
but the HASH does not correspond to any known bug.
Please double check the address.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 1/2] block: Verify whether blk_queue_enter() is used when necessary
2019-07-30 18:17 ` [PATCH 1/2] block: Verify whether blk_queue_enter() is used when necessary Bart Van Assche
@ 2019-07-31 1:46 ` Ming Lei
2019-07-31 18:26 ` Bart Van Assche
0 siblings, 1 reply; 8+ messages in thread
From: Ming Lei @ 2019-07-31 1:46 UTC (permalink / raw)
To: Bart Van Assche
Cc: Jens Axboe, linux-block, Christoph Hellwig, Tejun Heo,
Hannes Reinecke, Johannes Thumshirn, Alexandru Moise, Joseph Qi
On Tue, Jul 30, 2019 at 11:17:56AM -0700, Bart Van Assche wrote:
> It is required to protect blkg_lookup() calls with a blk_queue_enter() /
> blk_queue_exit() pair. Since it is nontrivial to verify whether this is
Could you explain the reason why the blk_queue_enter()/blk_queue_exit()
pair is required for blkg_lookup()? And comment on blkg_lookup() only
mentioned RCU read lock is needed.
The request queue reference counter is supposed to be held for any
caller of submit_bio(), why isn't that ref count enough?
Thanks,
Ming
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 2/2] block: Fix a race condition in submit_bio()
2019-07-30 18:17 ` [PATCH 2/2] block: Fix a race condition in submit_bio() Bart Van Assche
2019-07-30 18:18 ` syzbot
@ 2019-07-31 1:53 ` Ming Lei
2019-07-31 1:53 ` syzbot
1 sibling, 1 reply; 8+ messages in thread
From: Ming Lei @ 2019-07-31 1:53 UTC (permalink / raw)
To: Bart Van Assche
Cc: Jens Axboe, linux-block, Christoph Hellwig, Tejun Heo,
Hannes Reinecke, Johannes Thumshirn, Alexandru Moise, Joseph Qi,
syzbot+ff9ab4a23afa7553
On Tue, Jul 30, 2019 at 11:17:57AM -0700, Bart Van Assche wrote:
> generic_make_request_checks() needs to be protected by a
> blk_queue_enter() / blk_queue_exit() pair because it calls
> blkcg_bio_issue_check() and because that last function calls
> blkg_lookup().
>
> This patch fixes https://syzkaller.appspot.com/bug?id=ff9ab4a23afa7553fb79f745a92be87ba4144508.
>
> This patch also fixes the following kernel warning, triggered by
> blktests:
>
> WARNING: CPU: 5 PID: 10706 at block/blk-core.c:903 generic_make_request_checks+0x9c6/0xe60
> RIP: 0010:generic_make_request_checks+0x9c6/0xe60
> Call Trace:
> generic_make_request+0x7a/0x5c0
> submit_bio+0x92/0x280
> mpage_readpages+0x2b1/0x300
> blkdev_readpages+0x1d/0x20
> read_pages+0xd9/0x2c0
> __do_page_cache_readahead+0x2e0/0x310
> force_page_cache_readahead+0xfb/0x170
> page_cache_sync_readahead+0x28d/0x2a0
> generic_file_read_iter+0xc13/0x1530
> blkdev_read_iter+0x7d/0x90
> new_sync_read+0x2c5/0x3d0
> __vfs_read+0x7b/0x90
> vfs_read+0xc6/0x1f0
> ksys_read+0xc3/0x160
> __x64_sys_read+0x43/0x50
> do_syscall_64+0x71/0x270
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: Hannes Reinecke <hare@suse.com>
> Cc: Johannes Thumshirn <jthumshirn@suse.de>
> Cc: Alexandru Moise <00moses.alexander00@gmail.com>
> Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
> Reported-by: syzbot+ff9ab4a23afa7553@syzkaller.appspotmail.com
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
> block/blk-core.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index ff27c3080348..cd844c54e9f1 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1150,6 +1150,9 @@ EXPORT_SYMBOL_GPL(direct_make_request);
> */
> blk_qc_t submit_bio(struct bio *bio)
> {
> + struct request_queue *q = bio->bi_disk->queue;
> + blk_qc_t ret;
> +
> if (blkcg_punt_bio_submit(bio))
> return BLK_QC_T_NONE;
>
> @@ -1182,7 +1185,15 @@ blk_qc_t submit_bio(struct bio *bio)
> }
> }
>
> - return generic_make_request(bio);
> + if (unlikely(blk_queue_enter(q, 0) < 0)) {
> + bio->bi_status = BLK_STS_IOERR;
> + bio->bi_end_io(bio);
> + return BLK_QC_T_NONE;
> + }
> + ret = generic_make_request(bio);
> + blk_queue_exit(q);
No, nested blk_queue_enter() is easy to cause deadlock.
Thanks,
Ming
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Re: [PATCH 2/2] block: Fix a race condition in submit_bio()
2019-07-31 1:53 ` Ming Lei
@ 2019-07-31 1:53 ` syzbot
0 siblings, 0 replies; 8+ messages in thread
From: syzbot @ 2019-07-31 1:53 UTC (permalink / raw)
To: Ming Lei
Cc: 00moses.alexander00, axboe, bvanassche, hare, hch, joseph.qi,
jthumshirn, linux-block, ming.lei, tj
> On Tue, Jul 30, 2019 at 11:17:57AM -0700, Bart Van Assche wrote:
>> generic_make_request_checks() needs to be protected by a
>> blk_queue_enter() / blk_queue_exit() pair because it calls
>> blkcg_bio_issue_check() and because that last function calls
>> blkg_lookup().
>> This patch fixes
>> https://syzkaller.appspot.com/bug?id=ff9ab4a23afa7553fb79f745a92be87ba4144508.
>> This patch also fixes the following kernel warning, triggered by
>> blktests:
>> WARNING: CPU: 5 PID: 10706 at block/blk-core.c:903
>> generic_make_request_checks+0x9c6/0xe60
>> RIP: 0010:generic_make_request_checks+0x9c6/0xe60
>> Call Trace:
>> generic_make_request+0x7a/0x5c0
>> submit_bio+0x92/0x280
>> mpage_readpages+0x2b1/0x300
>> blkdev_readpages+0x1d/0x20
>> read_pages+0xd9/0x2c0
>> __do_page_cache_readahead+0x2e0/0x310
>> force_page_cache_readahead+0xfb/0x170
>> page_cache_sync_readahead+0x28d/0x2a0
>> generic_file_read_iter+0xc13/0x1530
>> blkdev_read_iter+0x7d/0x90
>> new_sync_read+0x2c5/0x3d0
>> __vfs_read+0x7b/0x90
>> vfs_read+0xc6/0x1f0
>> ksys_read+0xc3/0x160
>> __x64_sys_read+0x43/0x50
>> do_syscall_64+0x71/0x270
>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> Cc: Tejun Heo <tj@kernel.org>
>> Cc: Christoph Hellwig <hch@lst.de>
>> Cc: Ming Lei <ming.lei@redhat.com>
>> Cc: Hannes Reinecke <hare@suse.com>
>> Cc: Johannes Thumshirn <jthumshirn@suse.de>
>> Cc: Alexandru Moise <00moses.alexander00@gmail.com>
>> Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
>> Reported-by: syzbot+ff9ab4a23afa7553@syzkaller.appspotmail.com
>> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
>> ---
>> block/blk-core.c | 13 ++++++++++++-
>> 1 file changed, 12 insertions(+), 1 deletion(-)
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index ff27c3080348..cd844c54e9f1 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -1150,6 +1150,9 @@ EXPORT_SYMBOL_GPL(direct_make_request);
>> */
>> blk_qc_t submit_bio(struct bio *bio)
>> {
>> + struct request_queue *q = bio->bi_disk->queue;
>> + blk_qc_t ret;
>> +
>> if (blkcg_punt_bio_submit(bio))
>> return BLK_QC_T_NONE;
>> @@ -1182,7 +1185,15 @@ blk_qc_t submit_bio(struct bio *bio)
>> }
>> }
>> - return generic_make_request(bio);
>> + if (unlikely(blk_queue_enter(q, 0) < 0)) {
>> + bio->bi_status = BLK_STS_IOERR;
>> + bio->bi_end_io(bio);
>> + return BLK_QC_T_NONE;
>> + }
>> + ret = generic_make_request(bio);
>> + blk_queue_exit(q);
> No, nested blk_queue_enter() is easy to cause deadlock.
> Thanks,
> Ming
I see the command but can't find the corresponding bug.
The email is sent to syzbot+HASH@syzkaller.appspotmail.com address
but the HASH does not correspond to any known bug.
Please double check the address.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 1/2] block: Verify whether blk_queue_enter() is used when necessary
2019-07-31 1:46 ` Ming Lei
@ 2019-07-31 18:26 ` Bart Van Assche
0 siblings, 0 replies; 8+ messages in thread
From: Bart Van Assche @ 2019-07-31 18:26 UTC (permalink / raw)
To: Ming Lei
Cc: Jens Axboe, linux-block, Christoph Hellwig, Tejun Heo,
Hannes Reinecke, Johannes Thumshirn, Alexandru Moise, Joseph Qi
On 7/30/19 6:46 PM, Ming Lei wrote:
> On Tue, Jul 30, 2019 at 11:17:56AM -0700, Bart Van Assche wrote:
>> It is required to protect blkg_lookup() calls with a blk_queue_enter() /
>> blk_queue_exit() pair. Since it is nontrivial to verify whether this is
>
> Could you explain the reason why the blk_queue_enter()/blk_queue_exit()
> pair is required for blkg_lookup()? And comment on blkg_lookup() only
> mentioned RCU read lock is needed.
>
> The request queue reference counter is supposed to be held for any
> caller of submit_bio(), why isn't that ref count enough?
This patch was added to my own tree before commit
47cdee29ef9d ("block: move blk_exit_queue into __blk_release_queue")
went upstream. Since blk_exit_queue() has been moved from
blk_cleanup_queue() into __blk_release_queue() I don' think that we
need this patch series. I will drop these two patches.
Bart.
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2019-07-31 18:26 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-07-30 18:17 [PATCH 0/2] Fix a race condition triggered by submit_bio() Bart Van Assche
2019-07-30 18:17 ` [PATCH 1/2] block: Verify whether blk_queue_enter() is used when necessary Bart Van Assche
2019-07-31 1:46 ` Ming Lei
2019-07-31 18:26 ` Bart Van Assche
2019-07-30 18:17 ` [PATCH 2/2] block: Fix a race condition in submit_bio() Bart Van Assche
2019-07-30 18:18 ` syzbot
2019-07-31 1:53 ` Ming Lei
2019-07-31 1:53 ` syzbot
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