* [PATCH] lockdep: Remove unnecessary acquisitions wrt workqueue flush
@ 2017-09-07 0:33 Byungchul Park
2017-09-07 9:41 ` Peter Zijlstra
0 siblings, 1 reply; 5+ messages in thread
From: Byungchul Park @ 2017-09-07 0:33 UTC (permalink / raw)
To: tj, johannes.berg, peterz, mingo
Cc: tglx, oleg, david, linux-kernel, kernel-team
Workqueue added manual acquisitions to catch deadlock cases. Now
crossrelease was introduced, some of those are redundant because
crossrelease-enabled wait_for_completeion() also does it. Removed it.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
include/linux/workqueue.h | 4 ++--
kernel/workqueue.c | 16 +++++++---------
2 files changed, 9 insertions(+), 11 deletions(-)
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index db6dc9d..1bef13e 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -218,7 +218,7 @@ static inline void destroy_delayed_work_on_stack(struct delayed_work *work) { }
\
__init_work((_work), _onstack); \
(_work)->data = (atomic_long_t) WORK_DATA_INIT(); \
- lockdep_init_map(&(_work)->lockdep_map, #_work, &__key, 0); \
+ lockdep_init_map(&(_work)->lockdep_map, "(complete)"#_work, &__key, 0); \
INIT_LIST_HEAD(&(_work)->entry); \
(_work)->func = (_func); \
} while (0)
@@ -398,7 +398,7 @@ enum {
static struct lock_class_key __key; \
const char *__lock_name; \
\
- __lock_name = #fmt#args; \
+ __lock_name = "(complete)"#fmt#args; \
\
__alloc_workqueue_key((fmt), (flags), (max_active), \
&__key, __lock_name, ##args); \
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index ab3c0dc..ea4e9b6 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2503,8 +2503,8 @@ static void insert_wq_barrier(struct pool_workqueue *pwq,
* 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);
+ target->lockdep_map.name,
+ target->lockdep_map.key, 0);
__init_completion(&barr->done);
barr->task = current;
@@ -2611,16 +2611,17 @@ void flush_workqueue(struct workqueue_struct *wq)
struct wq_flusher this_flusher = {
.list = LIST_HEAD_INIT(this_flusher.list),
.flush_color = -1,
- .done = COMPLETION_INITIALIZER_ONSTACK(this_flusher.done),
};
int next_color;
+ lockdep_init_map_crosslock((struct lockdep_map *)&this_flusher.done.map,
+ wq->lockdep_map.name,
+ wq->lockdep_map.key, 0);
+ __init_completion(&this_flusher.done);
+
if (WARN_ON(!wq_online))
return;
- lock_map_acquire(&wq->lockdep_map);
- lock_map_release(&wq->lockdep_map);
-
mutex_lock(&wq->mutex);
/*
@@ -2883,9 +2884,6 @@ bool flush_work(struct work_struct *work)
if (WARN_ON(!wq_online))
return false;
- lock_map_acquire(&work->lockdep_map);
- lock_map_release(&work->lockdep_map);
-
if (start_flush_work(work, &barr)) {
wait_for_completion(&barr.done);
destroy_work_on_stack(&barr.work);
--
1.9.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] lockdep: Remove unnecessary acquisitions wrt workqueue flush
2017-09-07 0:33 [PATCH] lockdep: Remove unnecessary acquisitions wrt workqueue flush Byungchul Park
@ 2017-09-07 9:41 ` Peter Zijlstra
2017-09-07 11:37 ` Byungchul Park
0 siblings, 1 reply; 5+ messages in thread
From: Peter Zijlstra @ 2017-09-07 9:41 UTC (permalink / raw)
To: Byungchul Park
Cc: tj, johannes.berg, mingo, tglx, oleg, david, linux-kernel, kernel-team
On Thu, Sep 07, 2017 at 09:33:16AM +0900, Byungchul Park wrote:
> Workqueue added manual acquisitions to catch deadlock cases. Now
> crossrelease was introduced, some of those are redundant because
> crossrelease-enabled wait_for_completeion() also does it. Removed it.
This does not explain how it doesn't become the regular timing dependent
stuff cross-release normally is.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] lockdep: Remove unnecessary acquisitions wrt workqueue flush
2017-09-07 9:41 ` Peter Zijlstra
@ 2017-09-07 11:37 ` Byungchul Park
2017-09-07 15:21 ` Peter Zijlstra
0 siblings, 1 reply; 5+ messages in thread
From: Byungchul Park @ 2017-09-07 11:37 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Byungchul Park, Tejun Heo, johannes.berg, Ingo Molnar,
Thomas Gleixner, oleg, david, linux-kernel, kernel-team
On Thu, Sep 7, 2017 at 6:41 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Sep 07, 2017 at 09:33:16AM +0900, Byungchul Park wrote:
>> Workqueue added manual acquisitions to catch deadlock cases. Now
>> crossrelease was introduced, some of those are redundant because
>> crossrelease-enabled wait_for_completeion() also does it. Removed it.
>
> This does not explain how it doesn't become the regular timing dependent
> stuff cross-release normally is.
Yes, I will add more explanation for it at the next spin.
But, let me explain it a bit here to help you get it, since it's very
simple. This has nothing to do with 'might' thing I introduced
previously. For 'might' thing, I will start it after getting your response.
Here, I just removed acquire() because wait_for_completion()
already includes the acquire() by LOCKDEP_COMPLETIONS.
That's all.
--
Thanks,
Byungchul
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] lockdep: Remove unnecessary acquisitions wrt workqueue flush
2017-09-07 11:37 ` Byungchul Park
@ 2017-09-07 15:21 ` Peter Zijlstra
2017-09-07 21:19 ` Byungchul Park
0 siblings, 1 reply; 5+ messages in thread
From: Peter Zijlstra @ 2017-09-07 15:21 UTC (permalink / raw)
To: Byungchul Park
Cc: Byungchul Park, Tejun Heo, johannes.berg, Ingo Molnar,
Thomas Gleixner, oleg, david, linux-kernel, kernel-team
On Thu, Sep 07, 2017 at 08:37:08PM +0900, Byungchul Park wrote:
> On Thu, Sep 7, 2017 at 6:41 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> > On Thu, Sep 07, 2017 at 09:33:16AM +0900, Byungchul Park wrote:
> >> Workqueue added manual acquisitions to catch deadlock cases. Now
> >> crossrelease was introduced, some of those are redundant because
> >> crossrelease-enabled wait_for_completeion() also does it. Removed it.
> >
> > This does not explain how it doesn't become the regular timing dependent
> > stuff cross-release normally is.
>
> Yes, I will add more explanation for it at the next spin.
>
> But, let me explain it a bit here to help you get it, since it's very
> simple. This has nothing to do with 'might' thing I introduced
> previously. For 'might' thing, I will start it after getting your response.
>
> Here, I just removed acquire() because wait_for_completion()
> already includes the acquire() by LOCKDEP_COMPLETIONS.
> That's all.
Ah I see, but it does so using some fairly nasty completion init stuff.
The old code was far easier to read.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] lockdep: Remove unnecessary acquisitions wrt workqueue flush
2017-09-07 15:21 ` Peter Zijlstra
@ 2017-09-07 21:19 ` Byungchul Park
0 siblings, 0 replies; 5+ messages in thread
From: Byungchul Park @ 2017-09-07 21:19 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Byungchul Park, Tejun Heo, johannes.berg, Ingo Molnar,
Thomas Gleixner, oleg, david, linux-kernel, kernel-team
On Fri, Sep 8, 2017 at 12:21 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Sep 07, 2017 at 08:37:08PM +0900, Byungchul Park wrote:
>> On Thu, Sep 7, 2017 at 6:41 PM, Peter Zijlstra <peterz@infradead.org> wrote:
>> > On Thu, Sep 07, 2017 at 09:33:16AM +0900, Byungchul Park wrote:
>> >> Workqueue added manual acquisitions to catch deadlock cases. Now
>> >> crossrelease was introduced, some of those are redundant because
>> >> crossrelease-enabled wait_for_completeion() also does it. Removed it.
>> >
>> > This does not explain how it doesn't become the regular timing dependent
>> > stuff cross-release normally is.
>>
>> Yes, I will add more explanation for it at the next spin.
>>
>> But, let me explain it a bit here to help you get it, since it's very
>> simple. This has nothing to do with 'might' thing I introduced
>> previously. For 'might' thing, I will start it after getting your response.
>>
>> Here, I just removed acquire() because wait_for_completion()
>> already includes the acquire() by LOCKDEP_COMPLETIONS.
>> That's all.
>
> Ah I see, but it does so using some fairly nasty completion init stuff.
> The old code was far easier to read.
Agree.
But, old code has redundant acquisitions, moreover uses sub-class
to avoid false detection, even though they are the same class.
I will try to enhance readability of completion init, and fix the incorrect
use at the next spin.
--
Thanks,
Byungchul
^ permalink raw reply [flat|nested] 5+ messages in thread
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2017-09-07 0:33 [PATCH] lockdep: Remove unnecessary acquisitions wrt workqueue flush Byungchul Park
2017-09-07 9:41 ` Peter Zijlstra
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2017-09-07 15:21 ` Peter Zijlstra
2017-09-07 21:19 ` Byungchul Park
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