From: Byungchul Park <byungchul.park@lge.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: <mingo@kernel.org>, <tglx@linutronix.de>, <walken@google.com>,
<boqun.feng@gmail.com>, <kirill@shutemov.name>,
<linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
<iamjoonsoo.kim@lge.com>, <akpm@linux-foundation.org>,
<npiggin@gmail.com>, <kernel-team@lge.com>
Subject: Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature
Date: Wed, 1 Mar 2017 21:27:23 +0900 [thread overview]
Message-ID: <20170301122723.GK11663@X58A-UD3R> (raw)
In-Reply-To: <20170301104328.GD6515@twins.programming.kicks-ass.net>
On Wed, Mar 01, 2017 at 11:43:28AM +0100, Peter Zijlstra wrote:
> On Wed, Mar 01, 2017 at 04:21:28PM +0900, Byungchul Park wrote:
> > On Tue, Feb 28, 2017 at 07:15:47PM +0100, Peter Zijlstra wrote:
> > > On Wed, Jan 18, 2017 at 10:17:32PM +0900, Byungchul Park wrote:
> > > > + /*
> > > > + * Each work of workqueue might run in a different context,
> > > > + * thanks to concurrency support of workqueue. So we have to
> > > > + * distinguish each work to avoid false positive.
> > > > + *
> > > > + * TODO: We can also add dependencies between two acquisitions
> > > > + * of different work_id, if they don't cause a sleep so make
> > > > + * the worker stalled.
> > > > + */
> > > > + unsigned int work_id;
> > >
> > > > +/*
> > > > + * Crossrelease needs to distinguish each work of workqueues.
> > > > + * Caller is supposed to be a worker.
> > > > + */
> > > > +void crossrelease_work_start(void)
> > > > +{
> > > > + if (current->xhlocks)
> > > > + current->work_id++;
> > > > +}
> > >
> > > So what you're trying to do with that 'work_id' thing is basically wipe
> > > the entire history when we're at the bottom of a context.
> >
> > Sorry, but I do not understand what you are trying to say.
> >
> > What I was trying to do with the 'work_id' is to distinguish between
> > different works, which will be used to check if history locks were held
> > in the same context as a release one.
>
> The effect of changing work_id is that history disappears, yes? That is,
> by changing it, all our hist_locks don't match the context anymore and
> therefore we have no history.
Right. Now I understood your words.
> This is a useful operation.
>
> You would want to do this at points where you know there will not be any
> dependencies on prior action, and typically at the same points we want
> to not be holding any locks.
>
> Hence my term: 'bottom of a context', referring to an empty (held) lock
> stack.
Right.
> I would say this needs to be done for all 'work-queue' like things, and
Of course.
> there are quite a few outside of the obvious ones, smpboot threads and
> many other kthreads fall into this category.
Where can I check those?
> Similarly the return to userspace point that I already mentioned.
>
> I would propose something like:
>
> lockdep_assert_empty();
>
> Or something similar, which would verify the lock stack is indeed empty
> and wipe our entire hist_lock buffer when cross-release is enabled.
Right. I should do that.
> > > Which is a useful operation, but should arguably also be done on the
> > > return to userspace path. Any historical lock from before the current
> > > syscall is irrelevant.
Let me think more. It looks not a simple problem.
> >
> > Sorry. Could you explain it more?
>
> Does the above make things clear?
Perfect. Thank you very much.
next prev parent reply other threads:[~2017-03-01 12:29 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-18 13:17 [PATCH v5 00/13] lockdep: Implement crossrelease feature Byungchul Park
2017-01-18 13:17 ` [PATCH v5 01/13] lockdep: Refactor lookup_chain_cache() Byungchul Park
2017-01-19 9:16 ` Boqun Feng
2017-01-19 9:52 ` Byungchul Park
2017-01-26 7:53 ` Byungchul Park
2017-01-18 13:17 ` [PATCH v5 02/13] lockdep: Fix wrong condition to print bug msgs for MAX_LOCKDEP_CHAIN_HLOCKS Byungchul Park
2017-01-18 13:17 ` [PATCH v5 03/13] lockdep: Add a function building a chain between two classes Byungchul Park
2017-01-18 13:17 ` [PATCH v5 04/13] lockdep: Refactor save_trace() Byungchul Park
2017-01-18 13:17 ` [PATCH v5 05/13] lockdep: Pass a callback arg to check_prev_add() to handle stack_trace Byungchul Park
2017-01-26 7:43 ` Byungchul Park
2017-01-18 13:17 ` [PATCH v5 06/13] lockdep: Implement crossrelease feature Byungchul Park
2017-02-28 12:26 ` Peter Zijlstra
2017-02-28 12:45 ` Peter Zijlstra
2017-02-28 12:49 ` Peter Zijlstra
2017-03-01 6:20 ` Byungchul Park
2017-02-28 13:05 ` Peter Zijlstra
2017-02-28 13:28 ` Byungchul Park
2017-02-28 13:35 ` Peter Zijlstra
2017-02-28 14:00 ` Byungchul Park
2017-02-28 13:10 ` Peter Zijlstra
2017-02-28 13:24 ` Byungchul Park
2017-02-28 18:29 ` Peter Zijlstra
2017-03-01 4:40 ` Byungchul Park
2017-03-01 10:45 ` Peter Zijlstra
2017-03-01 12:10 ` Byungchul Park
2017-02-28 13:40 ` Peter Zijlstra
2017-03-01 5:43 ` Byungchul Park
2017-03-01 12:28 ` Peter Zijlstra
2017-03-02 13:40 ` Peter Zijlstra
2017-03-03 0:17 ` Byungchul Park
2017-03-03 8:14 ` Peter Zijlstra
2017-03-03 9:13 ` Peter Zijlstra
2017-03-03 9:32 ` Peter Zijlstra
2017-03-05 3:33 ` Byungchul Park
2017-08-10 12:18 ` [tip:locking/core] locking/lockdep: Avoid creating redundant links tip-bot for Peter Zijlstra
2017-03-05 3:08 ` [PATCH v5 06/13] lockdep: Implement crossrelease feature Byungchul Park
2017-03-07 11:42 ` Peter Zijlstra
2017-03-03 0:39 ` Byungchul Park
2017-02-28 15:49 ` Peter Zijlstra
2017-03-01 5:17 ` Byungchul Park
2017-03-01 6:18 ` Byungchul Park
2017-03-02 2:52 ` Byungchul Park
2017-02-28 18:15 ` Peter Zijlstra
2017-03-01 7:21 ` Byungchul Park
2017-03-01 10:43 ` Peter Zijlstra
2017-03-01 12:27 ` Byungchul Park [this message]
2017-03-02 4:20 ` Matthew Wilcox
2017-03-02 4:45 ` byungchul.park
2017-03-02 14:39 ` Matthew Wilcox
2017-03-02 23:50 ` Byungchul Park
2017-03-05 8:01 ` Byungchul Park
2017-03-14 7:36 ` Byungchul Park
2017-03-02 13:41 ` Peter Zijlstra
2017-03-02 23:43 ` Byungchul Park
2017-01-18 13:17 ` [PATCH v5 07/13] lockdep: Make print_circular_bug() aware of crossrelease Byungchul Park
2017-01-18 13:17 ` [PATCH v5 08/13] lockdep: Apply crossrelease to completions Byungchul Park
2017-01-18 13:17 ` [PATCH v5 09/13] pagemap.h: Remove trailing white space Byungchul Park
2017-01-18 13:17 ` [PATCH v5 10/13] lockdep: Apply crossrelease to PG_locked locks Byungchul Park
2017-01-18 13:17 ` [PATCH v5 11/13] lockdep: Apply lock_acquire(release) on __Set(__Clear)PageLocked Byungchul Park
2017-01-18 13:17 ` [PATCH v5 12/13] lockdep: Move data of CONFIG_LOCKDEP_PAGELOCK from page to page_ext Byungchul Park
2017-01-18 13:17 ` [PATCH v5 13/13] lockdep: Crossrelease feature documentation Byungchul Park
2017-01-20 9:08 ` [REVISED DOCUMENT] " Byungchul Park
2017-02-20 8:38 ` [PATCH v5 00/13] lockdep: Implement crossrelease feature Byungchul Park
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