Commit-ID: 52fa5bc5cbba089f09bc2c372e3432f3f3e48051 Gitweb: http://git.kernel.org/tip/52fa5bc5cbba089f09bc2c372e3432f3f3e48051 Author: Boqun Feng <boqun.f...@gmail.com> AuthorDate: Thu, 17 Aug 2017 17:46:12 +0800 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Thu, 17 Aug 2017 12:12:33 +0200
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 <mi...@kernel.org> Signed-off-by: Boqun Feng <boqun.f...@gmail.com> Cc: Byungchul Park <byungchul.p...@lge.com> Cc: Lai Jiangshan <jiangshan...@gmail.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Tejun Heo <t...@kernel.org> Cc: Thomas Gleixner <t...@linutronix.de> Link: http://lkml.kernel.org/r/20170817094622.12915-1-boqun.f...@gmail.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- include/linux/lockdep.h | 1 + kernel/workqueue.c | 11 ++++++++++- 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h index 651cc61..fc827ca 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. diff --git a/kernel/workqueue.c b/kernel/workqueue.c index e86733a..f128b3b 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -2476,7 +2476,16 @@ static void insert_wq_barrier(struct pool_workqueue *pwq, */ INIT_WORK_ONSTACK(&barr->work, wq_barrier_func); __set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work)); - init_completion(&barr->done); + + /* + * Explicitly init the crosslock for wq_barrier::done, make its lock + * key a subkey of the corresponding work. As a result we won't + * build a dependency between wq_barrier::done and unrelated work. + */ + lockdep_init_map_crosslock((struct lockdep_map *)&barr->done.map, + "(complete)wq_barr::done", + target->lockdep_map.key, 1); + __init_completion(&barr->done); barr->task = current; /*
