From: David Howells <dhowells@redhat.com>
To: Christian Schoenebeck <linux_oss@crudebyte.com>
Cc: dhowells@redhat.com, Pierre Barre <pierre@barre.sh>,
Dominique Martinet <asmadeus@codewreck.org>,
ericvh@kernel.org, lucho@ionkov.net, v9fs@lists.linux.dev,
linux-kernel@vger.kernel.org
Subject: Re: [BUG] 9p: data corruption with cache=mmap under concurrent stat/write
Date: Mon, 05 Jan 2026 07:54:23 +0000 [thread overview]
Message-ID: <1696785.1767599663@warthog.procyon.org.uk> (raw)
In-Reply-To: <5951517.DvuYhMxLoT@weasel>
Christian Schoenebeck <linux_oss@crudebyte.com> wrote:
> > > 2. Both getattr and setattr call filemap_fdatawrite() which initiates
> > >
> > > writeback but doesn't wait for completion. The subsequent server
> > > stat/wstat sees stale file size.
> > >
> > > Would using filemap_write_and_wait() instead be the correct fix?
>
> ... you are seeing a 2nd issue? getattr() output should not be related to
> mmap() access.
getattr() may flush outstanding dirty data on an inode so that the stats are
correct - but if so, it should wait for completion. If you look at cifs and
nfs, those uses filemap_datawait() or filemap_write_and_wait(), rather then
filemap_datawrite().
You might also want to check flags & AT_STATX_FORCE_SYNC and flags &
AT_STATX_DONT_SYNC.
I really ought to make afs honour AT_STATX_FORCE_SYNC.
David
prev parent reply other threads:[~2026-01-05 7:54 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-24 14:29 [BUG] 9p: data corruption with cache=mmap under concurrent stat/write Pierre Barre
2025-12-24 22:33 ` Dominique Martinet
2025-12-25 10:23 ` Christian Schoenebeck
2025-12-25 14:52 ` Pierre Barre
2025-12-26 13:13 ` Pierre Barre
2026-01-05 7:54 ` David Howells [this message]
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