From: Peter Zijlstra <peterz@infradead.org>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
Andrea Parri <parri.andrea@gmail.com>
Subject: Re: [RFC tip/locking/lockdep v5 05/17] lockdep: Extend __bfs() to work with multiple kinds of dependencies
Date: Thu, 22 Feb 2018 16:51:43 +0100 [thread overview]
Message-ID: <20180222155143.GV25235@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180222153034.GO25181@hirez.programming.kicks-ass.net>
On Thu, Feb 22, 2018 at 04:30:34PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 22, 2018 at 11:12:10PM +0800, Boqun Feng wrote:
> > On Thu, Feb 22, 2018 at 03:26:14PM +0100, Peter Zijlstra wrote:
>
> > > However, I would suggest:
> > >
> > > static inline bool is_xr(u16 dep)
> > > {
> > > return !!(dep & (DEP_NR_MASK | DEP_RR_MASK));
> > > }
> > >
> > > static inline bool is_rx(u16 dep)
> > > {
> > > return !!(dep & (DEP_RN_MASK | DEP_RR_MASK));
> > > }
> > >
> > > /* Skip *R -> R* relations */
> > > if (have_xr && is_rx(entry->dep))
> > > continue;
> >
> > I don't think this works, if we pick a *R for previous entry, and for
> > current entry, we have RR, NN and NR, your approach will skip the
> > current entry, but actually we can pick NN or NR (of course, in __bfs(),
> > we can greedily pick NN, because if NR causes a deadlock, so does NN).
>
> I don't get it, afaict my suggestion is identical.
>
> You skip condition: pick_dep() < 0, evaluates to:
>
> is_rr && (!NN_MASK && !NR_MASK) :=
> is_rr && (RN_MASK | RR_MASK)
>
> Which is exactly what I have.
Ooh, I think I see what I did wrong, would something like:
if (have_xr && !is_nx(entry-dep))
work? That's a lot harder to argue about though, still much better than
that tri-state pick thing.
> If that is satisfied, you set entry->is_rr to pick_dep(), which his
> harder to evaluate, but is something like:
>
> is_rr && NR_MASK || !(NN_MASK | RN_MASK) :=
> is_rr && NR_MASK || (NR_MASK | RR_MASK) :=
> (NR_MASK | RR_MASK)
>
> (because is_rr && RR_MASK will have been skipped)
>
> > >
> > > entry->have_xr = is_xr(entry->dep);
This one I think is still correct though.
next prev parent reply other threads:[~2018-02-22 15:51 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-22 7:08 [RFC tip/locking/lockdep v5 00/17] lockdep: Support deadlock detection for recursive read locks Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 01/17] lockdep: Demagic the return value of BFS Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 02/17] lockdep: Make __bfs() visit every dependency until a match Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 03/17] lockdep: Redefine LOCK_*_STATE* bits Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 04/17] lockdep: Introduce lock_list::dep Boqun Feng
2018-02-23 11:55 ` Peter Zijlstra
2018-02-23 12:37 ` Boqun Feng
2018-02-24 5:32 ` Boqun Feng
2018-02-24 6:30 ` Boqun Feng
2018-02-24 8:38 ` Peter Zijlstra
2018-02-24 9:00 ` Boqun Feng
2018-02-24 9:26 ` Boqun Feng
2018-02-26 9:00 ` Peter Zijlstra
2018-02-26 10:15 ` Boqun Feng
2018-02-26 10:20 ` Boqun Feng
2018-02-24 7:31 ` Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 05/17] lockdep: Extend __bfs() to work with multiple kinds of dependencies Boqun Feng
2018-02-22 14:26 ` Peter Zijlstra
2018-02-22 15:12 ` Boqun Feng
2018-02-22 15:30 ` Peter Zijlstra
2018-02-22 15:51 ` Peter Zijlstra [this message]
2018-02-22 16:31 ` Boqun Feng
2018-02-23 5:02 ` Boqun Feng
2018-02-23 11:15 ` Peter Zijlstra
2018-02-22 16:08 ` Peter Zijlstra
2018-02-22 16:34 ` Boqun Feng
2018-02-22 16:32 ` Peter Zijlstra
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 06/17] lockdep: Support deadlock detection for recursive read in check_noncircular() Boqun Feng
2018-02-22 14:54 ` Peter Zijlstra
2018-02-22 15:16 ` Peter Zijlstra
2018-02-22 15:44 ` Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 07/17] lockdep: Adjust check_redundant() for recursive read change Boqun Feng
2018-02-22 17:29 ` Peter Zijlstra
2018-03-16 8:20 ` Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 08/17] lockdep: Fix recursive read lock related safe->unsafe detection Boqun Feng
2018-02-22 17:41 ` Peter Zijlstra
2018-02-22 17:46 ` Peter Zijlstra
2018-02-23 8:21 ` Boqun Feng
2018-02-23 8:58 ` Boqun Feng
2018-02-23 11:36 ` Peter Zijlstra
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 09/17] lockdep: Add recursive read locks into dependency graph Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 10/17] lockdep/selftest: Add a R-L/L-W test case specific to chain cache behavior Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 11/17] lockdep: Take read/write status in consideration when generate chainkey Boqun Feng
2018-02-22 7:08 ` [RFC tip/locking/lockdep v5 12/17] lockdep/selftest: Unleash irq_read_recursion2 and add more Boqun Feng
2018-02-22 7:09 ` [RFC tip/locking/lockdep v5 13/17] lockdep/selftest: Add more recursive read related test cases Boqun Feng
2018-02-22 7:09 ` [RFC tip/locking/lockdep v5 14/17] Revert "locking/lockdep/selftests: Fix mixed read-write ABBA tests" Boqun Feng
2018-02-22 7:09 ` [RFC tip/locking/lockdep v5 15/17] lockdep: Reduce the size of lock_list Boqun Feng
2018-02-23 11:38 ` Peter Zijlstra
2018-02-23 12:40 ` Boqun Feng
2018-02-22 7:09 ` [RFC tip/locking/lockdep v5 16/17] lockdep: Documention for recursive read lock detection reasoning Boqun Feng
2018-02-24 22:53 ` Andrea Parri
2018-02-27 2:32 ` Boqun Feng
2018-02-22 7:09 ` [RFC tip/locking/lockdep v5 17/17] MAINTAINERS: Add myself as a LOCKING PRIMITIVES reviewer Boqun Feng
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