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From: Peter Zijlstra <peterz@infradead.org>
To: Byungchul Park <byungchul.park@lge.com>
Cc: Boqun Feng <boqun.feng@gmail.com>,
	mingo@kernel.org, tglx@linutronix.de, walken@google.com,
	kirill@shutemov.name, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, iamjoonsoo.kim@lge.com,
	akpm@linux-foundation.org, npiggin@gmail.com
Subject: Re: [PATCH v4 15/15] lockdep: Crossrelease feature documentation
Date: Wed, 18 Jan 2017 13:07:57 +0100	[thread overview]
Message-ID: <20170118120757.GD6515@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20170118115428.GM3326@X58A-UD3R>

On Wed, Jan 18, 2017 at 08:54:28PM +0900, Byungchul Park wrote:
> On Wed, Jan 18, 2017 at 12:03:17PM +0100, Peter Zijlstra wrote:
> > On Wed, Jan 18, 2017 at 07:53:47PM +0900, Byungchul Park wrote:
> > > On Wed, Jan 18, 2017 at 02:42:30PM +0800, Boqun Feng wrote:
> > > > On Fri, Dec 09, 2016 at 02:12:11PM +0900, Byungchul Park wrote:
> > > > [...]
> > > > > +Example 1:
> > > > > +
> > > > > +   CONTEXT X		   CONTEXT Y
> > > > > +   ---------		   ---------
> > > > > +   mutext_lock A
> > > > > +			   lock_page B
> > > > > +   lock_page B
> > > > > +			   mutext_lock A /* DEADLOCK */
> > > > 
> > > > s/mutext_lock/mutex_lock
> > > 
> > > Thank you.
> > > 
> > > > > +Example 3:
> > > > > +
> > > > > +   CONTEXT X		   CONTEXT Y
> > > > > +   ---------		   ---------
> > > > > +			   mutex_lock A
> > > > > +   mutex_lock A
> > > > > +   mutex_unlock A
> > > > > +			   wait_for_complete B /* DEADLOCK */
> > > > 
> > > > I think this part better be:
> > > > 
> > > >    CONTEXT X		   CONTEXT Y
> > > >    ---------		   ---------
> > > >    			   mutex_lock A
> > > >    mutex_lock A
> > > >    			   wait_for_complete B /* DEADLOCK */
> > > >    mutex_unlock A
> > > > 
> > > > , right? Because Y triggers DEADLOCK before X could run mutex_unlock().
> > > 
> > > There's no different between two examples.
> > 
> > There is..
> > 
> > > No matter which one is chosen, mutex_lock A in CONTEXT X cannot be passed.
> > 
> > But your version shows it does mutex_unlock() before CONTEXT Y does
> > wait_for_completion().
> > 
> > The thing about these diagrams is that both columns are assumed to have
> > the same timeline.
> 
> X cannot acquire mutex A because Y already acquired it.
> 
> In order words, all statements below mutex_lock A in X cannot run.

But your timeline shows it does, which is the error that Boqun pointed
out.

WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Byungchul Park <byungchul.park@lge.com>
Cc: Boqun Feng <boqun.feng@gmail.com>,
	mingo@kernel.org, tglx@linutronix.de, walken@google.com,
	kirill@shutemov.name, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, iamjoonsoo.kim@lge.com,
	akpm@linux-foundation.org, npiggin@gmail.com
Subject: Re: [PATCH v4 15/15] lockdep: Crossrelease feature documentation
Date: Wed, 18 Jan 2017 13:07:57 +0100	[thread overview]
Message-ID: <20170118120757.GD6515@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20170118115428.GM3326@X58A-UD3R>

On Wed, Jan 18, 2017 at 08:54:28PM +0900, Byungchul Park wrote:
> On Wed, Jan 18, 2017 at 12:03:17PM +0100, Peter Zijlstra wrote:
> > On Wed, Jan 18, 2017 at 07:53:47PM +0900, Byungchul Park wrote:
> > > On Wed, Jan 18, 2017 at 02:42:30PM +0800, Boqun Feng wrote:
> > > > On Fri, Dec 09, 2016 at 02:12:11PM +0900, Byungchul Park wrote:
> > > > [...]
> > > > > +Example 1:
> > > > > +
> > > > > +   CONTEXT X		   CONTEXT Y
> > > > > +   ---------		   ---------
> > > > > +   mutext_lock A
> > > > > +			   lock_page B
> > > > > +   lock_page B
> > > > > +			   mutext_lock A /* DEADLOCK */
> > > > 
> > > > s/mutext_lock/mutex_lock
> > > 
> > > Thank you.
> > > 
> > > > > +Example 3:
> > > > > +
> > > > > +   CONTEXT X		   CONTEXT Y
> > > > > +   ---------		   ---------
> > > > > +			   mutex_lock A
> > > > > +   mutex_lock A
> > > > > +   mutex_unlock A
> > > > > +			   wait_for_complete B /* DEADLOCK */
> > > > 
> > > > I think this part better be:
> > > > 
> > > >    CONTEXT X		   CONTEXT Y
> > > >    ---------		   ---------
> > > >    			   mutex_lock A
> > > >    mutex_lock A
> > > >    			   wait_for_complete B /* DEADLOCK */
> > > >    mutex_unlock A
> > > > 
> > > > , right? Because Y triggers DEADLOCK before X could run mutex_unlock().
> > > 
> > > There's no different between two examples.
> > 
> > There is..
> > 
> > > No matter which one is chosen, mutex_lock A in CONTEXT X cannot be passed.
> > 
> > But your version shows it does mutex_unlock() before CONTEXT Y does
> > wait_for_completion().
> > 
> > The thing about these diagrams is that both columns are assumed to have
> > the same timeline.
> 
> X cannot acquire mutex A because Y already acquired it.
> 
> In order words, all statements below mutex_lock A in X cannot run.

But your timeline shows it does, which is the error that Boqun pointed
out.

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  reply	other threads:[~2017-01-18 12:29 UTC|newest]

Thread overview: 104+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-09  5:11 [PATCH v4 00/15] lockdep: Implement crossrelease feature Byungchul Park
2016-12-09  5:11 ` Byungchul Park
2016-12-09  5:11 ` [PATCH v4 01/15] x86/dumpstack: Optimize save_stack_trace Byungchul Park
2016-12-09  5:11   ` Byungchul Park
2016-12-09  5:11 ` [PATCH v4 02/15] x86/dumpstack: Add save_stack_trace()_fast() Byungchul Park
2016-12-09  5:11   ` Byungchul Park
2016-12-09  5:11 ` [PATCH v4 03/15] lockdep: Refactor lookup_chain_cache() Byungchul Park
2016-12-09  5:11   ` Byungchul Park
2016-12-09  5:12 ` [PATCH v4 04/15] lockdep: Add a function building a chain between two classes Byungchul Park
2016-12-09  5:12   ` Byungchul Park
2017-01-10 21:00   ` Peter Zijlstra
2017-01-10 21:00     ` Peter Zijlstra
2017-01-12  1:41     ` Byungchul Park
2017-01-12  1:41       ` Byungchul Park
2016-12-09  5:12 ` [PATCH v4 05/15] lockdep: Make check_prev_add can use a separate stack_trace Byungchul Park
2016-12-09  5:12   ` Byungchul Park
2017-01-12 16:16   ` Peter Zijlstra
2017-01-12 16:16     ` Peter Zijlstra
2017-01-13  2:45     ` Byungchul Park
2017-01-13  2:45       ` Byungchul Park
2017-01-13  4:09     ` [PATCH] lockdep: Make a stack_trace instance passed to check_prev_add as an arg Byungchul Park
2017-01-13  4:38       ` Byungchul Park
2017-01-13 10:11     ` [PATCH v4 05/15] lockdep: Make check_prev_add can use a separate stack_trace Byungchul Park
2017-01-13 10:11       ` Byungchul Park
2017-01-13 10:17       ` [PATCH 1/2] lockdep: Refactor save_trace() Byungchul Park
2017-01-13 10:17       ` [PATCH 2/2] lockdep: Pass a callback arg to check_prev_add() to handle stack_trace Byungchul Park
2017-01-17 15:54       ` [PATCH v4 05/15] lockdep: Make check_prev_add can use a separate stack_trace Peter Zijlstra
2017-01-17 15:54         ` Peter Zijlstra
2017-01-18  2:04         ` Byungchul Park
2017-01-18  2:04           ` Byungchul Park
2017-01-18 15:10           ` Peter Zijlstra
2017-01-18 15:10             ` Peter Zijlstra
2017-01-19  2:47             ` Byungchul Park
2017-01-19  2:47               ` Byungchul Park
2016-12-09  5:12 ` [PATCH v4 06/15] lockdep: Make save_trace can skip stack tracing of the current Byungchul Park
2016-12-09  5:12   ` Byungchul Park
2017-01-12 16:37   ` Peter Zijlstra
2017-01-12 16:37     ` Peter Zijlstra
2017-01-13  0:18     ` Byungchul Park
2017-01-13  0:18       ` Byungchul Park
2016-12-09  5:12 ` [PATCH v4 07/15] lockdep: Implement crossrelease feature Byungchul Park
2016-12-09  5:12   ` Byungchul Park
2017-01-13  4:39   ` Lai Jiangshan
2017-01-13  4:39     ` Lai Jiangshan
2017-01-13  5:02     ` Byungchul Park
2017-01-13  5:02       ` Byungchul Park
2017-01-16 15:10   ` Peter Zijlstra
2017-01-16 15:10     ` Peter Zijlstra
2017-01-17  2:05     ` Byungchul Park
2017-01-17  2:05       ` Byungchul Park
2017-01-17  7:12       ` Peter Zijlstra
2017-01-17  7:12         ` Peter Zijlstra
2017-01-17  7:49         ` Byungchul Park
2017-01-17  7:49           ` Byungchul Park
2017-01-17  7:14       ` Peter Zijlstra
2017-01-17  7:14         ` Peter Zijlstra
2017-01-17  7:45         ` Byungchul Park
2017-01-17  7:45           ` Byungchul Park
2017-01-16 15:13   ` Peter Zijlstra
2017-01-16 15:13     ` Peter Zijlstra
2017-01-17  2:33     ` Byungchul Park
2017-01-17  2:33       ` Byungchul Park
2017-01-17  6:24       ` Boqun Feng
2017-01-17  7:43         ` Byungchul Park
2017-01-17  7:43           ` Byungchul Park
2016-12-09  5:12 ` [PATCH v4 08/15] lockdep: Make crossrelease use save_stack_trace_fast() Byungchul Park
2016-12-09  5:12   ` Byungchul Park
2016-12-09  5:12 ` [PATCH v4 09/15] lockdep: Make print_circular_bug() crosslock-aware Byungchul Park
2016-12-09  5:12   ` Byungchul Park
2016-12-09  5:12 ` [PATCH v4 10/15] lockdep: Apply crossrelease to completion operation Byungchul Park
2016-12-09  5:12   ` Byungchul Park
2016-12-09  5:12 ` [PATCH v4 11/15] pagemap.h: Remove trailing white space Byungchul Park
2016-12-09  5:12   ` Byungchul Park
2016-12-09  5:12 ` [PATCH v4 12/15] lockdep: Apply crossrelease to PG_locked lock Byungchul Park
2016-12-09  5:12   ` Byungchul Park
2016-12-09  5:12 ` [PATCH v4 13/15] lockdep: Apply lock_acquire(release) on __Set(__Clear)PageLocked Byungchul Park
2016-12-09  5:12   ` Byungchul Park
2016-12-09  5:12 ` [PATCH v4 14/15] lockdep: Move data used in CONFIG_LOCKDEP_PAGELOCK from page to page_ext Byungchul Park
2016-12-09  5:12   ` Byungchul Park
2016-12-09  5:12 ` [PATCH v4 15/15] lockdep: Crossrelease feature documentation Byungchul Park
2016-12-09  5:12   ` Byungchul Park
2017-01-10 20:08   ` Peter Zijlstra
2017-01-10 20:08     ` Peter Zijlstra
2017-01-11  1:29     ` Byungchul Park
2017-01-11  1:29       ` Byungchul Park
2017-01-18  6:42   ` Boqun Feng
2017-01-18 10:53     ` Byungchul Park
2017-01-18 10:53       ` Byungchul Park
2017-01-18 11:03       ` Peter Zijlstra
2017-01-18 11:03         ` Peter Zijlstra
2017-01-18 11:54         ` Byungchul Park
2017-01-18 11:54           ` Byungchul Park
2017-01-18 12:07           ` Peter Zijlstra [this message]
2017-01-18 12:07             ` Peter Zijlstra
2017-01-18 12:14             ` byungchul.park
2017-01-18 12:14               ` byungchul.park
2017-01-18 14:12               ` Peter Zijlstra
2017-01-18 14:12                 ` Peter Zijlstra
2017-01-19  1:54                 ` Byungchul Park
2017-01-19  1:54                   ` Byungchul Park
2017-01-18 12:49             ` byungchul.park
2017-01-18 12:49               ` byungchul.park
2016-12-09  5:21 ` [FYI] Output of 'cat /proc/lockdep' after applying crossrelease Byungchul Park
2016-12-09  5:21   ` Byungchul Park

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