From: Matthew Wilcox <willy@infradead.org>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Will Deacon <will@kernel.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
Ard Biesheuvel <ardb@kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Alan Stern <stern@rowland.harvard.edu>,
Andrea Parri <parri.andrea@gmail.com>,
Peter Zijlstra <peterz@infradead.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>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-arch <linux-arch@vger.kernel.org>,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v4 2/2] change buffer_locked, so that it has acquire semantics
Date: Mon, 1 Aug 2022 15:37:12 +0100 [thread overview]
Message-ID: <YuflGG60pHiXp2z/@casper.infradead.org> (raw)
In-Reply-To: <alpine.LRH.2.02.2208010642220.22006@file01.intranet.prod.int.rdu2.redhat.com>
On Mon, Aug 01, 2022 at 06:43:55AM -0400, Mikulas Patocka wrote:
> Let's have a look at this piece of code in __bread_slow:
> get_bh(bh);
> bh->b_end_io = end_buffer_read_sync;
> submit_bh(REQ_OP_READ, 0, bh);
> wait_on_buffer(bh);
> if (buffer_uptodate(bh))
> return bh;
> Neither wait_on_buffer nor buffer_uptodate contain any memory barrier.
> Consequently, if someone calls sb_bread and then reads the buffer data,
> the read of buffer data may be executed before wait_on_buffer(bh) on
> architectures with weak memory ordering and it may return invalid data.
>
> Fix this bug by changing the function buffer_locked to have the acquire
> semantics - so that code that follows buffer_locked cannot be moved before
> it.
I think this is the wrong approach. Instead, buffer_set_uptodate()
should have the smp_wmb() and buffer_uptodate should have the smp_rmb().
Just like the page flags. As I said last night.
next prev parent reply other threads:[~2022-08-01 14:37 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-31 11:43 [PATCH] Add a read memory barrier to wait_on_buffer Mikulas Patocka
2022-07-31 12:00 ` Ard Biesheuvel
2022-07-31 13:41 ` Mikulas Patocka
2022-07-31 15:08 ` [PATCH v2] make buffer_locked provide an acquire semantics Mikulas Patocka
2022-07-31 16:51 ` Linus Torvalds
2022-07-31 17:30 ` Paul E. McKenney
2022-07-31 22:48 ` Matthew Wilcox
2022-08-01 3:20 ` Paul E. McKenney
2022-08-01 15:41 ` Will Deacon
2022-08-01 19:20 ` Paul E. McKenney
2022-08-02 8:54 ` Will Deacon
2022-08-02 13:49 ` Paul E. McKenney
2022-08-02 15:29 ` Paul E. McKenney
2022-07-31 20:39 ` Mikulas Patocka
2022-07-31 20:40 ` [PATCH v3 1/2] wait_bit: do read barrier after testing a bit Mikulas Patocka
2022-07-31 20:57 ` Linus Torvalds
2022-08-01 10:40 ` Mikulas Patocka
2022-08-01 10:43 ` [PATCH v4 2/2] change buffer_locked, so that it has acquire semantics Mikulas Patocka
2022-08-01 14:37 ` Matthew Wilcox [this message]
2022-08-01 15:01 ` Mikulas Patocka
2022-08-05 3:22 ` Matthew Wilcox
2022-08-07 11:37 ` [PATCH v5] add barriers to buffer functions Mikulas Patocka
2022-08-07 14:50 ` Matthew Wilcox
2022-08-08 14:26 ` Mikulas Patocka
2022-08-08 14:40 ` Matthew Wilcox
2022-08-08 14:57 ` Mikulas Patocka
2022-08-08 15:31 ` Paul E. McKenney
2022-08-08 15:39 ` Matthew Wilcox
2022-08-09 18:32 ` [PATCH v6] add barriers to buffer_uptodate and set_buffer_uptodate Mikulas Patocka
2022-08-09 19:44 ` Matthew Wilcox
2022-08-09 22:06 ` Linus Torvalds
2022-08-01 10:42 ` [PATCH v4 1/2] introduce test_bit_acquire and use it in wait_on_bit Mikulas Patocka
2022-08-01 15:54 ` Will Deacon
2022-08-01 16:12 ` Mikulas Patocka
2022-08-01 18:17 ` Boqun Feng
2022-08-02 8:00 ` David Laight
2022-08-02 8:40 ` Will Deacon
2022-08-02 11:38 ` Mikulas Patocka
2022-08-02 13:36 ` Will Deacon
2022-08-02 15:57 ` Mikulas Patocka
2022-08-01 0:27 ` [PATCH v3 1/2] wait_bit: do read barrier after testing a bit Alan Stern
2022-07-31 20:43 ` [PATCH v3 2/2] make buffer_locked provide an acquire semantics Mikulas Patocka
2022-07-31 20:51 ` Linus Torvalds
2022-07-31 22:14 ` Matthew Wilcox
2022-07-31 22:31 ` Ard Biesheuvel
2022-07-31 22:48 ` Ard Biesheuvel
2022-07-31 20:46 ` [PATCH v2] " Linus Torvalds
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