[PATCH AUTOSEL for 4.9 151/190] block/mq: Cure cpu hotplug lock inversion

2018-03-07 Thread Sasha Levin 
From: Peter Zijlstra 

[ 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: [] 
static_key_slow_dec+0x1b/0x50
 []
 [] but task is already holding lock:
 []  (>s_type->i_mutex_key#4){+.}, at: [] 
sched_feat_write+0x86/0x170
 []
 [] which lock already depends on the new lock.
 []
 []
 [] the existing dependency chain (in reverse order) is:
 []
 [] -> #2 (>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: [] 
vfs_write+0x17d/0x1a0
 []  #1:  (debugfs_srcu){..}, at: [] 
full_proxy_write+0x5d/0xd0
 []  #2:  (>s_type->i_mutex_key#4){+.}, at: [] 
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 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin 
---
 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(_q_mutex);
+   get_online_cpus();
 
list_add_tail(>all_q_node, _q_list);
blk_mq_add_queue_tag_set(set, q);
blk_mq_map_swqueue(q, cpu_online_mask);
 
-   mutex_unlock(_q_mutex);
put_online_cpus();
+   mutex_unlock(_q_mutex);
 
return q;
 
-- 
2.14.1

[PATCH AUTOSEL for 4.9 151/190] block/mq: Cure cpu hotplug lock inversion

2018-03-07 Thread Sasha Levin 
From: Peter Zijlstra 

[ 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: [] 
static_key_slow_dec+0x1b/0x50
 []
 [] but task is already holding lock:
 []  (>s_type->i_mutex_key#4){+.}, at: [] 
sched_feat_write+0x86/0x170
 []
 [] which lock already depends on the new lock.
 []
 []
 [] the existing dependency chain (in reverse order) is:
 []
 [] -> #2 (>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: [] 
vfs_write+0x17d/0x1a0
 []  #1:  (debugfs_srcu){..}, at: [] 
full_proxy_write+0x5d/0xd0
 []  #2:  (>s_type->i_mutex_key#4){+.}, at: [] 
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 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin 
---
 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(_q_mutex);
+   get_online_cpus();
 
list_add_tail(>all_q_node, _q_list);
blk_mq_add_queue_tag_set(set, q);
blk_mq_map_swqueue(q, cpu_online_mask);
 
-   mutex_unlock(_q_mutex);
put_online_cpus();
+   mutex_unlock(_q_mutex);
 
return q;
 
-- 
2.14.1