The commit 80e96c5484be (dm thin: do not allow thin device activation while pool is suspended) delayed the initialization of the completion and setting the initial refcount to 1 until after the new thin is added to the pool's active thins list and the pool lock is released. This opens a race with a worker thread that walks the list and calls thin_get/put, noticing that the refcount goes to 0 and calling complete, freezing up the system and giving the oops below: kernel: BUG: unable to handle kernel NULL pointer dereference at (null) kernel: IP: [<ffffffff810d360b>] __wake_up_common+0x2b/0x90 kernel: Call Trace: kernel: [<ffffffff810d3683>] __wake_up_locked+0x13/0x20 kernel: [<ffffffff810d3dc7>] complete+0x37/0x50 kernel: [<ffffffffa0595c50>] thin_put+0x20/0x30 [dm_thin_pool] kernel: [<ffffffffa059aab7>] do_worker+0x667/0x870 [dm_thin_pool] kernel: [<ffffffff816a8a4c>] ? __schedule+0x3ac/0x9a0 kernel: [<ffffffff810b1aef>] process_one_work+0x14f/0x400 kernel: [<ffffffff810b206b>] worker_thread+0x6b/0x490 kernel: [<ffffffff810b2000>] ? rescuer_thread+0x260/0x260 kernel: [<ffffffff810b6a7b>] kthread+0xdb/0x100 kernel: [<ffffffff810b69a0>] ? kthread_create_on_node+0x170/0x170 kernel: [<ffffffff816ad7ec>] ret_from_fork+0x7c/0xb0 kernel: [<ffffffff810b69a0>] ? kthread_create_on_node+0x170/0x170 Set the initial refcount and initialize the completion before dropping the pool lock. Signed-off-by: Marc Dionne <marc.dionne@xxxxxxxxxxxxxxxxxxxx> --- drivers/md/dm-thin.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c index 8735543..4133223 100644 --- a/drivers/md/dm-thin.c +++ b/drivers/md/dm-thin.c @@ -3814,6 +3814,8 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv) r = -EINVAL; goto bad; } + atomic_set(&tc->refcount, 1); + init_completion(&tc->can_destroy); list_add_tail_rcu(&tc->list, &tc->pool->active_thins); spin_unlock_irqrestore(&tc->pool->lock, flags); /* @@ -3826,9 +3828,6 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv) dm_put(pool_md); - atomic_set(&tc->refcount, 1); - init_completion(&tc->can_destroy); - return 0; bad: -- 2.1.0 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
