From 52fa5bc5cbba089f09bc2c372e3432f3f3e48051 Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Thu, 17 Aug 2017 17:46:12 +0800 Subject: locking/lockdep: Explicitly initialize wq_barrier::done::map With the new lockdep crossrelease feature, which checks completions usage, a false positive is reported in the workqueue code: > Worker A : acquired of wfc.work -> wait for cpu_hotplug_lock to be released > Task B : acquired of cpu_hotplug_lock -> wait for lock#3 to be released > Task C : acquired of lock#3 -> wait for completion of barr->done > (Task C is in lru_add_drain_all_cpuslocked()) > Worker D : wait for wfc.work to be released -> will complete barr->done Such a dead lock can not happen because Task C's barr->done and Worker D's barr->done can not be the same instance. The reason of this false positive is we initialize all wq_barrier::done at insert_wq_barrier() via init_completion(), which makes them belong to the same lock class, therefore, impossible circles are reported. To fix this, explicitly initialize the lockdep map for wq_barrier::done in insert_wq_barrier(), so that the lock class key of wq_barrier::done is a subkey of the corresponding work_struct, as a result we won't build a dependency between a wq_barrier with a unrelated work, and we can differ wq barriers based on the related works, so the false positive above is avoided. Also define the empty lockdep_init_map_crosslock() for !CROSSRELEASE to make the code simple and away from unnecessary #ifdefs. Reported-by: Ingo Molnar Signed-off-by: Boqun Feng Cc: Byungchul Park Cc: Lai Jiangshan Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Tejun Heo Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20170817094622.12915-1-boqun.feng@gmail.com Signed-off-by: Ingo Molnar --- include/linux/lockdep.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/lockdep.h') diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h index 651cc61af041..fc827cab6d6e 100644 --- a/include/linux/lockdep.h +++ b/include/linux/lockdep.h @@ -583,6 +583,7 @@ extern void crossrelease_hist_end(enum xhlock_context_t c); extern void lockdep_init_task(struct task_struct *task); extern void lockdep_free_task(struct task_struct *task); #else +#define lockdep_init_map_crosslock(m, n, k, s) do {} while (0) /* * To initialize a lockdep_map statically use this macro. * Note that _name must not be NULL. -- cgit v1.2.3-59-g8ed1b