* [PATCH] workqueue/lockdep: Explicitly initialize wq_barrier::done::map
@ 2017-08-17 9:46 Boqun Feng
2017-08-17 10:22 ` [tip:locking/core] locking/lockdep: " tip-bot for Boqun Feng
2017-08-17 13:26 ` [PATCH] workqueue/lockdep: " Tejun Heo
0 siblings, 2 replies; 3+ messages in thread
From: Boqun Feng @ 2017-08-17 9:46 UTC (permalink / raw)
To: linux-kernel
Cc: Boqun Feng, Byungchul Park, Peter Zijlstra, Ingo Molnar,
Tejun Heo, Lai Jiangshan
With CROSSRELEASE feature introduced, such a potential deadlock is
reported:
> 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
However, given this very case, such a dead lock could not happen because
Task C's barr->done and Worker D's barr->done can not be the same
instance. So this is a false positive.
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@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Cc: Byungchul Park <byungchul.park@lge.com>
---
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 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.
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index e86733a8b344..861301c2b638 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 is a subkey of the corresponding work. As a result we won't
+ * build a dependency between a wq_barrier::done and a 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;
/*
--
2.14.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* [tip:locking/core] locking/lockdep: Explicitly initialize wq_barrier::done::map
2017-08-17 9:46 [PATCH] workqueue/lockdep: Explicitly initialize wq_barrier::done::map Boqun Feng
@ 2017-08-17 10:22 ` tip-bot for Boqun Feng
2017-08-17 13:26 ` [PATCH] workqueue/lockdep: " Tejun Heo
1 sibling, 0 replies; 3+ messages in thread
From: tip-bot for Boqun Feng @ 2017-08-17 10:22 UTC (permalink / raw)
To: linux-tip-commits
Cc: jiangshanlai, torvalds, byungchul.park, peterz, linux-kernel,
tglx, mingo, hpa, tj, boqun.feng
Commit-ID: 52fa5bc5cbba089f09bc2c372e3432f3f3e48051
Gitweb: http://git.kernel.org/tip/52fa5bc5cbba089f09bc2c372e3432f3f3e48051
Author: Boqun Feng <boqun.feng@gmail.com>
AuthorDate: Thu, 17 Aug 2017 17:46:12 +0800
Committer: Ingo Molnar <mingo@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 <mingo@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170817094622.12915-1-boqun.feng@gmail.com
Signed-off-by: Ingo Molnar <mingo@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;
/*
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] workqueue/lockdep: Explicitly initialize wq_barrier::done::map
2017-08-17 9:46 [PATCH] workqueue/lockdep: Explicitly initialize wq_barrier::done::map Boqun Feng
2017-08-17 10:22 ` [tip:locking/core] locking/lockdep: " tip-bot for Boqun Feng
@ 2017-08-17 13:26 ` Tejun Heo
1 sibling, 0 replies; 3+ messages in thread
From: Tejun Heo @ 2017-08-17 13:26 UTC (permalink / raw)
To: Boqun Feng
Cc: linux-kernel, Byungchul Park, Peter Zijlstra, Ingo Molnar, Lai Jiangshan
On Thu, Aug 17, 2017 at 05:46:12PM +0800, Boqun Feng wrote:
> With CROSSRELEASE feature introduced, such a potential deadlock is
> reported:
>
> > 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
>
> However, given this very case, such a dead lock could not happen because
> Task C's barr->done and Worker D's barr->done can not be the same
> instance. So this is a false positive.
>
> 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@kernel.org>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> Cc: Byungchul Park <byungchul.park@lge.com>
Acked-by: Tejun Heo <tj@kernel.org>
Thanks.
--
tejun
^ permalink raw reply [flat|nested] 3+ messages in thread
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