path: root/block
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authorWaiman Long <longman@redhat.com>2017-09-20 13:12:20 -0600
committerJens Axboe <axboe@kernel.dk>2017-09-25 08:56:05 -0600
commit5acb3cc2c2e9d3020a4fee43763c6463767f1572 (patch)
tree0d650e446e8e7ef738e3d2237b6778fb6ef447a4 /block
parentnbd: ignore non-nbd ioctl's (diff)
blktrace: Fix potential deadlock between delete & sysfs ops
The lockdep code had reported the following unsafe locking scenario: CPU0 CPU1 ---- ---- lock(s_active#228); lock(&bdev->bd_mutex/1); lock(s_active#228); lock(&bdev->bd_mutex); *** DEADLOCK *** The deadlock may happen when one task (CPU1) is trying to delete a partition in a block device and another task (CPU0) is accessing tracing sysfs file (e.g. /sys/block/dm-1/trace/act_mask) in that partition. The s_active isn't an actual lock. It is a reference count (kn->count) on the sysfs (kernfs) file. Removal of a sysfs file, however, require a wait until all the references are gone. The reference count is treated like a rwsem using lockdep instrumentation code. The fact that a thread is in the sysfs callback method or in the ioctl call means there is a reference to the opended sysfs or device file. That should prevent the underlying block structure from being removed. Instead of using bd_mutex in the block_device structure, a new blk_trace_mutex is now added to the request_queue structure to protect access to the blk_trace structure. Suggested-by: Christoph Hellwig <hch@infradead.org> Signed-off-by: Waiman Long <longman@redhat.com> Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Fix typo in patch subject line, and prune a comment detailing how the code used to work. Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
1 files changed, 3 insertions, 0 deletions
diff --git a/block/blk-core.c b/block/blk-core.c
index aebe676225e6..048be4aa6024 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -854,6 +854,9 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
kobject_init(&q->kobj, &blk_queue_ktype);
+ mutex_init(&q->blk_trace_mutex);