Messages in this thread Patch in this message | | | From | Waiman Long <> | Subject | [PATCH] debugobjects: Disable lockdep tracking of debugobjects internal locks | Date | Fri, 13 Jul 2018 09:42:27 -0400 |
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It was discovered that running the ltp openposix_testsuite sigqueue-09-1 test on a certain 8-sock IvyBridge system caused it to have a hard lockup with a full debug kernel.
[89981.861500] NMI watchdog: Watchdog detected hard LOCKUP on cpu 17 : [89981.939812] irq event stamp: 1166122 [89981.943799] hardirqs last enabled at (1166121): [<ffffffffb1048342>] kprobe_ftrace_handler+0x52/0x170 [89981.954215] hardirqs last disabled at (1166122): [<ffffffffb08a3725>] tasklist_write_lock_irq+0x15/0x50 : [89982.103134] [<ffffffffb093a399>] lock_acquire+0x99/0x1e0 [89982.109163] [<ffffffffb0c0d19b>] ? debug_check_no_obj_freed+0xfb/0x270 [89982.116562] [<ffffffffb1042e1e>] _raw_spin_lock_irqsave+0x5e/0xa0 [89982.123470] [<ffffffffb0c0d19b>] ? debug_check_no_obj_freed+0xfb/0x270 [89982.130851] [<ffffffffb0c0d19b>] debug_check_no_obj_freed+0xfb/0x270 [89982.138045] [<ffffffffb08bf9f3>] ? __sigqueue_free.part.11+0x33/0x40 [89982.145239] [<ffffffffb0a6868a>] kmem_cache_free+0xca/0x390 [89982.151553] [<ffffffffb08bf9f3>] __sigqueue_free.part.11+0x33/0x40 [89982.158552] [<ffffffffb08c07b0>] flush_sigqueue+0x50/0x60 [89982.164673] [<ffffffffb08ad102>] release_task+0x3e2/0x6d0 :
IRQ was disabled by the tasklist_write_lock_irq() call in release_task(). The lockup is probably caused by the debug code running for too long. We certainly want the debug code to verify the correctness of the production code. However, there may not have too much value for one piece of the debug code to verify the correctness of another piece of debug code. In this particular case, the lockdep code is verifying the correctness of the raw debug bucket lock within the debugobjects code.
The use of spin locks in the debugobjects code for synchronization is pretty standard and looks to be correct to me. So it is probably not worth the effort to verify lock usage within the debugobjects code.
This patch disables the checking of the debugobjects internal locks by lockdep. In fact, with this change, the hard lockup was not observed anymore.
Signed-off-by: Waiman Long <longman@redhat.com> --- lib/debugobjects.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/lib/debugobjects.c b/lib/debugobjects.c index 994be48..592d2ba 100644 --- a/lib/debugobjects.c +++ b/lib/debugobjects.c @@ -1103,8 +1103,15 @@ void __init debug_objects_early_init(void) { int i; - for (i = 0; i < ODEBUG_HASH_SIZE; i++) + /* + * We don't need lockdep to verify correctness of debugobjects + * internal locks. + */ + lockdep_set_novalidate_class(&pool_lock); + for (i = 0; i < ODEBUG_HASH_SIZE; i++) { raw_spin_lock_init(&obj_hash[i].lock); + lockdep_set_novalidate_class(&obj_hash[i].lock); + } for (i = 0; i < ODEBUG_POOL_SIZE; i++) hlist_add_head(&obj_static_pool[i].node, &obj_pool); -- 1.8.3.1
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