This is a note to let you know that I've just added the patch titled

block/mq: Cure cpu hotplug lock inversion

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: block-mq-cure-cpu-hotplug-lock-inversion.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Thu Mar 22 14:40:24 CET 2018

From: Peter Zijlstra peterz@infradead.org Date: Thu, 4 May 2017 15:05:26 +0200 Subject: block/mq: Cure cpu hotplug lock inversion

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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- block/blk-mq.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2014,15 +2014,15 @@ struct request_queue *blk_mq_init_alloca

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;

Patches currently in stable-queue which might be from peterz@infradead.org are

queue-4.9/acpi-processor-fix-error-handling-in-__acpi_processor_start.patch queue-4.9/x86-reboot-turn-off-kvm-when-halting-a-cpu.patch queue-4.9/block-mq-cure-cpu-hotplug-lock-inversion.patch queue-4.9/acpi-processor-replace-racy-task-affinity-logic.patch queue-4.9/perf-tests-kmod-path-don-t-fail-if-compressed-modules-aren-t-supported.patch queue-4.9/cpufreq-sh-replace-racy-task-affinity-logic.patch queue-4.9/x86-kaslr-fix-kexec-kernel-boot-crash-when-kaslr-randomization-fails.patch