From: Jann Horn <jannh@google.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: paulmck@kernel.org, Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linuxfoundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Suren Baghdasaryan <surenb@google.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Alan Stern <stern@rowland.harvard.edu>,
Andrea Parri <parri.andrea@gmail.com>,
Will Deacon <will@kernel.org>, Boqun Feng <boqun.feng@gmail.com>,
Nicholas Piggin <npiggin@gmail.com>,
David Howells <dhowells@redhat.com>,
Jade Alglave <j.alglave@ucl.ac.uk>,
Luc Maranget <luc.maranget@inria.fr>,
Akira Yokosawa <akiyks@gmail.com>,
Daniel Lustig <dlustig@nvidia.com>,
Joel Fernandes <joel@joelfernandes.org>
Subject: Re: [PATCH 0/2] fix vma->anon_vma check for per-VMA locking; fix anon_vma memory ordering
Date: Thu, 27 Jul 2023 17:15:45 +0200 [thread overview]
Message-ID: <CAG48ez1YPhc2sp=+pXCsZsmiPfXF_oQakouSfNFqi4xK2gEuGA@mail.gmail.com> (raw)
In-Reply-To: <ZMKINJ9+WX1WWG8g@casper.infradead.org>
On Thu, Jul 27, 2023 at 5:07 PM Matthew Wilcox <willy@infradead.org> wrote:
> On Thu, Jul 27, 2023 at 04:39:34PM +0200, Jann Horn wrote:
> > The other option is to replace the READ_ONCE() with a
> > smp_load_acquire(), at which point it becomes a lot simpler to show
> > that the code is correct.
>
> Aren't we straining at gnats here? The context of this is handling a
> page fault, and we used to take an entire rwsem for read. I'm having
> a hard time caring about "the extra expense" of an unnecessarily broad
> barrier.
>
> Cost of an L3 cacheline miss is in the thousands of cycles. Cost of a
> barrier is ... tens?
Yeah, fair point. If it's hard to show correctness with READ_ONCE() we
can just use smp_load_acquire() and call it a day.
next prev parent reply other threads:[~2023-07-27 15:16 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-26 21:41 [PATCH 0/2] fix vma->anon_vma check for per-VMA locking; fix anon_vma memory ordering Jann Horn
2023-07-26 21:41 ` [PATCH 1/2] mm: lock_vma_under_rcu() must check vma->anon_vma under vma lock Jann Horn
2023-07-27 21:52 ` Suren Baghdasaryan
2023-07-26 21:41 ` [PATCH 2/2] mm: Fix anon_vma memory ordering Jann Horn
2023-07-26 21:50 ` Jann Horn
2023-07-27 18:25 ` Linus Torvalds
2023-07-26 23:19 ` [PATCH 0/2] fix vma->anon_vma check for per-VMA locking; fix " Paul E. McKenney
2023-07-27 14:39 ` Jann Horn
2023-07-27 14:57 ` Will Deacon
2023-07-27 15:44 ` Alan Stern
2023-07-27 16:10 ` Jann Horn
2023-07-27 16:17 ` Paul E. McKenney
2023-07-27 16:16 ` Paul E. McKenney
2023-07-27 17:11 ` Linus Torvalds
2023-07-27 17:41 ` Alan Stern
2023-07-27 18:01 ` Linus Torvalds
2023-07-27 19:05 ` Nadav Amit
2023-07-27 19:39 ` Linus Torvalds
2023-07-27 20:11 ` Nadav Amit
2023-07-28 9:18 ` Nadav Amit
2023-07-27 15:07 ` Matthew Wilcox
2023-07-27 15:15 ` Jann Horn [this message]
2023-07-27 16:09 ` Paul E. McKenney
2023-07-27 16:34 Joel Fernandes
2023-07-28 12:44 ` Will Deacon
2023-07-28 17:35 ` Joel Fernandes
2023-07-28 17:51 ` Alan Stern
2023-07-28 18:03 ` Joel Fernandes
2023-07-28 18:18 ` Paul E. McKenney
2023-07-28 19:50 ` Joel Fernandes
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