* [PATCH v2 0/2] Fix a race condition triggered by submit_bio()
@ 2019-07-30 18:36 Bart Van Assche
2019-07-30 18:36 ` [PATCH v2 1/2] block: Verify whether blk_queue_enter() is used when necessary Bart Van Assche
2019-07-30 18:36 ` [PATCH v2 2/2] block: Fix a race condition in submit_bio() Bart Van Assche
0 siblings, 2 replies; 3+ messages in thread
From: Bart Van Assche @ 2019-07-30 18:36 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.
Changes compared to v1:
- Use the full syzbot ID in patch 2/2 instead of abbreviating it.
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] 3+ messages in thread
* [PATCH v2 1/2] block: Verify whether blk_queue_enter() is used when necessary
2019-07-30 18:36 [PATCH v2 0/2] Fix a race condition triggered by submit_bio() Bart Van Assche
@ 2019-07-30 18:36 ` Bart Van Assche
2019-07-30 18:36 ` [PATCH v2 2/2] block: Fix a race condition in submit_bio() Bart Van Assche
1 sibling, 0 replies; 3+ messages in thread
From: Bart Van Assche @ 2019-07-30 18:36 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] 3+ messages in thread
* [PATCH v2 2/2] block: Fix a race condition in submit_bio()
2019-07-30 18:36 [PATCH v2 0/2] Fix a race condition triggered by submit_bio() Bart Van Assche
2019-07-30 18:36 ` [PATCH v2 1/2] block: Verify whether blk_queue_enter() is used when necessary Bart Van Assche
@ 2019-07-30 18:36 ` Bart Van Assche
1 sibling, 0 replies; 3+ messages in thread
From: Bart Van Assche @ 2019-07-30 18:36 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+21cfe1f803e0e158acf1
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+21cfe1f803e0e158acf1@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] 3+ messages in thread
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