On 1/4/21 10:38 AM, Peter Zijlstra wrote:
On Tue, Dec 22, 2020 at 05:55:53PM -0500, Waiman Long wrote:
The following lockdep splat was hit:
[ 560.638354] WARNING: CPU: 79 PID: 27458 at kernel/rcu/tree_plugin.h:1749
call_rcu+0x6dc/0xf00
:
[ 560.647761] RIP: 0010:call_rcu+0x6dc/0xf00
[ 560.647763] Code: 0f 8f 29 04 00 00 e8 93 da 1c 00 48 8b 3c 24 57 9d 0f 1f 44 00
00 e9 19 fa ff ff 65 8b 05 38 83 c4 49 85 c0 0f 84 cd fb ff ff <0f> 0b e9 c6 fb
ff ff e8 b8 45 51 00 4c 89 f2 48 b8 00 00 00 00 00
[ 560.647764] RSP: 0018:ff11001050097b58 EFLAGS: 00010002
[ 560.647766] RAX: 0000000000000001 RBX: ffffffffbb1f3360 RCX:
0000000000000001
[ 560.647766] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
ffffffffb99bac9c
[ 560.647767] RBP: 1fe220020a012f73 R08: 000000010004005c R09:
dffffc0000000000
[ 560.647768] R10: dffffc0000000000 R11: 0000000000000003 R12:
ff1100105b7f70e1
[ 560.647769] R13: ffffffffb635d8a0 R14: ff1100105b7f72d8 R15:
ff1100105b7f7040
[ 560.647770] FS: 00007fd9b3437080(0000) GS:ff1100105b600000(0000)
knlGS:0000000000000000
[ 560.647771] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 560.647772] CR2: 00007fd9b30112bc CR3: 000000105e898006 CR4:
0000000000761ee0
[ 560.647773] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[ 560.647773] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
0000000000000400
[ 560.647774] PKRU: 55555554
[ 560.647774] Call Trace:
[ 560.647778] ? invoke_rcu_core+0x180/0x180
[ 560.647782] ? __is_module_percpu_address+0xed/0x440
[ 560.647787] lockdep_unregister_key+0x2ab/0x5b0
[ 560.647791] destroy_workqueue+0x40b/0x610
[ 560.647862] xlog_dealloc_log+0x216/0x2b0 [xfs]
:
This splat is caused by the fact that lockdep_unregister_key() uses
raw_local_irq_save() which doesn't update the hardirqs_enabled
percpu flag. The call_rcu() function, however, will call
lockdep_assert_irqs_disabled() to check the hardirqs_enabled flag which
remained set in this case.
Fix this problem by using local_irq_save()/local_irq_restore() pairs
whenever call_rcu() is being called.
I'm not sure I much like all this,.. :/
I think raw_local_irq_save() function can be used if no external
function is being called except maybe printk() as it means another
lockdep problem exists.
The reason lockdep is using raw_local_irq_save() is to avoid calling
into itself again, notably local_irq_restore() will end up in
mark_held_locks().
Fixes: a0b0fd53e1e67 ("locking/lockdep: Free lock classes that are no longer in
use")
Seems dubious, as the lockdep_assert_irqs_disabled() that triggered was
added after that patch.
I'm thinking another solution would be to increment the lockdep
recursion count before calling RCU, because then we'll fail
__lockdep_enabled and the assertion gets killed. Hmm?
Yes, you are right. Incrementing the lockdep recursion count should fix
the issue. I was missing the commit 43be4388e94b ("lockdep: Put graph
lock/unlock under lock_recursion protection"). This commit will properly
increment the percpu lockdep recursion count and disable the call_rcu
warning. So please ignore this patch.
Thanks,
Longman
