From: Matthew Wilcox <willy@infradead.org>
To: Alex <alex.fcyrx@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
brauner@kernel.org, jack@suse.cz, torvalds@linux-foundation.org,
paulmck@kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] fs: Remove obsolete logic in i_size_read/write
Date: Wed, 16 Jul 2025 14:41:30 +0100 [thread overview]
Message-ID: <aHesCjzSInq8w757@casper.infradead.org> (raw)
In-Reply-To: <CAKawSAmp668+zUcaThnnhMtU8hmyTOKifHqxfE02WKYYpWxVHg@mail.gmail.com>
On Wed, Jul 16, 2025 at 09:28:29PM +0800, Alex wrote:
> On Wed, Jul 16, 2025 at 9:12 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > On Wed, Jul 16, 2025 at 08:53:04PM +0800, Alex wrote:
> > > The logic is used to protect load/store tearing on 32 bit platforms,
> > > for example, after i_size_read returned, there is no guarantee that
> > > inode->size won't be changed. Therefore, READ/WRITE_ONCE suffice, which
> > > is already implied by smp_load_acquire/smp_store_release.
> >
> > Sorry, what? The problem is not a _later_ change, it's getting the
> > upper and lower 32bit halves from different values.
> >
> > Before: position is 0xffffffff
> > After: position is 0x100000000
> > The value that might be returned by your variant: 0x1ffffffff.
>
> I mean the sequence lock here is used to only avoid load/store tearing,
> smp_load_acquire/smp_store_release already protects that.
Why do you think that? You're wrong, but it'd be useful to understand
what misled you into thinking that.
next prev parent reply other threads:[~2025-07-16 13:41 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-16 12:53 [PATCH] fs: Remove obsolete logic in i_size_read/write Alex
2025-07-16 13:12 ` Al Viro
2025-07-16 13:28 ` Alex
2025-07-16 13:41 ` Matthew Wilcox [this message]
2025-07-16 13:44 ` Alex
2025-07-16 13:57 ` Matthew Wilcox
2025-07-16 14:38 ` Alex
2025-07-17 5:05 ` kernel test robot
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