From: Byungchul Park <byungchul.park@lge.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, tj@kernel.org, boqun.feng@gmail.com,
david@fromorbit.com, johannes@sipsolutions.net, oleg@redhat.com,
linux-kernel@vger.kernel.org, kernel-team@lge.com
Subject: Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation
Date: Fri, 25 Aug 2017 10:11:14 +0900 [thread overview]
Message-ID: <20170825011114.GA3858@X58A-UD3R> (raw)
In-Reply-To: <20170824140240.t4imrpvussebfimm@hirez.programming.kicks-ass.net>
On Thu, Aug 24, 2017 at 04:02:40PM +0200, Peter Zijlstra wrote:
> On Thu, Aug 24, 2017 at 11:18:40AM +0900, Byungchul Park wrote:
> > On Wed, Aug 23, 2017 at 01:58:47PM +0200, Peter Zijlstra wrote:
>
> > > Also, unconditinoally switching to recursive-read here would fail to
> > > detect the actual deadlock on single-threaded workqueues, which do
> >
> > Do you mean it's true even in case having fixed lockdep properly?
> > Could you explain why if so? IMHO, I don't think so.
>
> I'm saying that if lockdep is fixed it should be:
>
> if (wq->saved_max_active == 1 || wq->rescuer) {
> lock_map_acquire(wq->lockdep_map);
> lock_map_acquire(lockdep_map);
> } else {
> lock_map_acquire_read(wq->lockdep_map);
> lock_map_acquire_read(lockdep_map);
> }
>
> or something like that, because for a single-threaded workqueue, the
> following _IS_ a deadlock:
>
> work-n:
> wait_for_completion(C);
>
> work-n+1:
> complete(C);
>
> And that is the only case we now fail to catch.
Thank you for explanation.
> > > +void crossrelease_hist_start(enum xhlock_context_t c, bool force)
> > > {
> > > struct task_struct *cur = current;
> > >
> > > - if (cur->xhlocks) {
> > > - cur->xhlock_idx_hist[c] = cur->xhlock_idx;
> > > - cur->hist_id_save[c] = cur->hist_id;
> > > + if (!cur->xhlocks)
> > > + return;
> > > +
> > > + /*
> > > + * We call this at an invariant point, no current state, no history.
> > > + */
> >
> > This very work-around code _must_ be removed after fixing read-recursive
> > thing in lockdep. I think it would be better to add a tag(comment)
> > saying it.
> >
> > > + if (c == XHLOCK_PROC) {
> > > + /* verified the former, ensure the latter */
> > > + WARN_ON_ONCE(!force && cur->lockdep_depth);
> > > + invalidate_xhlock(&xhlock(cur->xhlock_idx));
> > > }
>
> No, this is not a work around, this is fundamentally so. It's not going
> away. The only thing that should go away is the .force argument.
I meant, this seems to be led from your mis-understanding of
crossrelease_hist_{start, end}().
Uer of force == 1 should not exist or don't have to exist. I am sure you
haven't read my replys. Please read the following at least:
https://lkml.org/lkml/2017/8/24/126
next prev parent reply other threads:[~2017-08-25 1:11 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-23 11:58 [PATCH 0/4] workqueue and lockdep stuffs Peter Zijlstra
2017-08-23 11:58 ` [PATCH 1/4] workqueue: Use TASK_IDLE Peter Zijlstra
2017-08-23 13:31 ` Tejun Heo
2017-08-23 11:58 ` [PATCH 2/4] lockdep/selftests: Add mixed read-write ABBA tests Peter Zijlstra
2017-08-23 11:58 ` [PATCH 3/4] workqueue/lockdep: Fix flush_work() annotation Peter Zijlstra
2017-08-23 11:58 ` [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra
2017-08-24 2:18 ` Byungchul Park
2017-08-24 14:02 ` Peter Zijlstra
2017-08-25 1:11 ` Byungchul Park [this message]
2017-08-29 8:59 ` Peter Zijlstra
2017-08-29 14:23 ` [tip:locking/core] locking/lockdep: Untangle xhlock history save/restore from task independence tip-bot for Peter Zijlstra
2017-08-29 16:02 ` [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park
2017-08-29 18:47 ` Peter Zijlstra
2017-08-30 2:09 ` Byungchul Park
2017-08-30 7:41 ` Byungchul Park
2017-08-30 8:53 ` Peter Zijlstra
2017-08-30 9:01 ` Byungchul Park
2017-08-30 9:12 ` Peter Zijlstra
2017-08-30 9:14 ` Peter Zijlstra
2017-08-30 9:35 ` Byungchul Park
2017-08-30 9:24 ` Byungchul Park
2017-08-30 11:25 ` Byungchul Park
2017-08-30 12:49 ` Byungchul Park
2017-08-31 7:26 ` Byungchul Park
2017-08-31 8:04 ` Peter Zijlstra
2017-08-31 8:15 ` Byungchul Park
2017-08-31 8:34 ` Peter Zijlstra
2017-09-01 2:05 ` Byungchul Park
2017-09-01 9:47 ` Peter Zijlstra
2017-09-01 10:16 ` Byungchul Park
2017-09-01 12:09 ` 박병철/선임연구원/SW Platform(연)AOT팀(byungchul.park@lge.com)
2017-09-01 12:38 ` Peter Zijlstra
2017-09-01 13:51 ` Byungchul Park
2017-09-01 16:38 ` Peter Zijlstra
2017-09-04 1:30 ` Byungchul Park
2017-09-04 2:08 ` Byungchul Park
2017-09-04 11:42 ` Peter Zijlstra
2017-09-05 0:38 ` Byungchul Park
2017-09-05 7:08 ` Peter Zijlstra
2017-09-05 7:19 ` Peter Zijlstra
2017-09-05 8:57 ` Byungchul Park
2017-09-05 9:36 ` Peter Zijlstra
2017-09-05 10:31 ` Byungchul Park
2017-09-05 10:52 ` Peter Zijlstra
2017-09-05 11:24 ` Byungchul Park
2017-09-05 10:58 ` Byungchul Park
2017-09-05 13:46 ` Peter Zijlstra
2017-09-05 23:52 ` Byungchul Park
2017-09-06 0:42 ` Boqun Feng
2017-09-06 1:32 ` Byungchul Park
2017-09-06 23:59 ` Byungchul Park
2017-09-07 0:11 ` Byungchul Park
2017-09-06 0:48 ` Byungchul Park
2017-09-05 8:30 ` Byungchul Park
2017-08-31 8:07 ` Peter Zijlstra
2017-08-25 4:39 ` Byungchul Park
2017-08-29 6:46 ` Byungchul Park
2017-08-29 9:01 ` Peter Zijlstra
2017-08-29 16:12 ` Byungchul Park
2017-08-23 13:32 ` [PATCH 0/4] workqueue and lockdep stuffs Tejun Heo
2017-08-23 13:45 ` Peter Zijlstra
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