From: Peter Zijlstra peterz@infradead.org
[ Upstream commit eabe06595d62cfa9278e2cd012df614bc68a7042 ]
By poking at /debug/sched_features I triggered the following splat:
[] ====================================================== [] WARNING: possible circular locking dependency detected [] 4.11.0-00873-g964c8b7-dirty #694 Not tainted [] ------------------------------------------------------ [] bash/2109 is trying to acquire lock: [] (cpu_hotplug_lock.rw_sem){++++++}, at: [<ffffffff8120cb8b>] static_key_slow_dec+0x1b/0x50 [] [] but task is already holding lock: [] (&sb->s_type->i_mutex_key#4){+++++.}, at: [<ffffffff81140216>] sched_feat_write+0x86/0x170 [] [] which lock already depends on the new lock. [] [] [] the existing dependency chain (in reverse order) is: [] [] -> #2 (&sb->s_type->i_mutex_key#4){+++++.}: [] lock_acquire+0x100/0x210 [] down_write+0x28/0x60 [] start_creating+0x5e/0xf0 [] debugfs_create_dir+0x13/0x110 [] blk_mq_debugfs_register+0x21/0x70 [] blk_mq_register_dev+0x64/0xd0 [] blk_register_queue+0x6a/0x170 [] device_add_disk+0x22d/0x440 [] loop_add+0x1f3/0x280 [] loop_init+0x104/0x142 [] do_one_initcall+0x43/0x180 [] kernel_init_freeable+0x1de/0x266 [] kernel_init+0xe/0x100 [] ret_from_fork+0x31/0x40 [] [] -> #1 (all_q_mutex){+.+.+.}: [] lock_acquire+0x100/0x210 [] __mutex_lock+0x6c/0x960 [] mutex_lock_nested+0x1b/0x20 [] blk_mq_init_allocated_queue+0x37c/0x4e0 [] blk_mq_init_queue+0x3a/0x60 [] loop_add+0xe5/0x280 [] loop_init+0x104/0x142 [] do_one_initcall+0x43/0x180 [] kernel_init_freeable+0x1de/0x266 [] kernel_init+0xe/0x100 [] ret_from_fork+0x31/0x40
[] *** DEADLOCK *** [] [] 3 locks held by bash/2109: [] #0: (sb_writers#11){.+.+.+}, at: [<ffffffff81292bcd>] vfs_write+0x17d/0x1a0 [] #1: (debugfs_srcu){......}, at: [<ffffffff8155a90d>] full_proxy_write+0x5d/0xd0 [] #2: (&sb->s_type->i_mutex_key#4){+++++.}, at: [<ffffffff81140216>] sched_feat_write+0x86/0x170 [] [] stack backtrace: [] CPU: 9 PID: 2109 Comm: bash Not tainted 4.11.0-00873-g964c8b7-dirty #694 [] Hardware name: Intel Corporation S2600GZ/S2600GZ, BIOS SE5C600.86B.02.02.0002.122320131210 12/23/2013 [] Call Trace:
[] lock_acquire+0x100/0x210 [] get_online_cpus+0x2a/0x90 [] static_key_slow_dec+0x1b/0x50 [] static_key_disable+0x20/0x30 [] sched_feat_write+0x131/0x170 [] full_proxy_write+0x97/0xd0 [] __vfs_write+0x28/0x120 [] vfs_write+0xb5/0x1a0 [] SyS_write+0x49/0xa0 [] entry_SYSCALL_64_fastpath+0x23/0xc2
This is because of the cpu hotplug lock rework. Break the chain at #1 by reversing the lock acquisition order. This way i_mutex_key#4 no longer depends on cpu_hotplug_lock and things are good.
Cc: Jens Axboe axboe@kernel.dk Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Jens Axboe axboe@fb.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- block/blk-mq.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c index 10f8f94b7f20..c6572ffc1e87 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2014,15 +2014,15 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
blk_mq_init_cpu_queues(q, set->nr_hw_queues);
- get_online_cpus(); mutex_lock(&all_q_mutex); + get_online_cpus();
list_add_tail(&q->all_q_node, &all_q_list); blk_mq_add_queue_tag_set(set, q); blk_mq_map_swqueue(q, cpu_online_mask);
- mutex_unlock(&all_q_mutex); put_online_cpus(); + mutex_unlock(&all_q_mutex);
return q;