Commit-ID: 52fa5bc5cbba089f09bc2c372e3432f3f3e48051
Gitweb: http://git.kernel.org/tip/52fa5bc5cbba089f09bc2c372e3432f3f3e48051
Author: Boqun Feng <boqun.feng@xxxxxxxxx>
AuthorDate: Thu, 17 Aug 2017 17:46:12 +0800
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
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 <mingo@xxxxxxxxxx>
Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Byungchul Park <byungchul.park@xxxxxxx>
Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20170817094622.12915-1-boqun.feng@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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;
/*
--
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