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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <2226525.1789118704@warthog.procyon.org.uk> To: Dominique Martinet Cc: dhowells@redhat.com, Michael Mulqueen , ericvh@kernel.org, lucho@ionkov.net, pc@manguebit.org, linux_oss@crudebyte.com, v9fs@lists.linux.dev, netfs@lists.linux.dev, linux-fsdevel@vger.kernel.org, regressions@lists.linux.dev Subject: Re: PROBLEM: [REGRESSION 7.1-rc4 -> 7.1-rc5] 9p: silent NUL corruption of file data on cache modes with CACHE_WRITEBACK Precedence: bulk X-Mailing-List: v9fs@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Sun, 13 Sep 2026 08:55:13 +0100 Message-ID: <2718782.1789286113@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Mimecast-MFC-PROC-ID: NxKzfJGUWZxK842XnEBDUthDz4juKh4fYMM-lmnpe5M_1789286120 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="us-ascii" Content-ID: <2718781.1789286113.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Dominique Martinet wrote: > When v9fs_issue_write() is re-entered, writing the remaining data at the > original subreq->start offset rather than subreq->start + subreq->transfe= rred > would overwrite previously written data. Retry should now be resetting ->transferred to 0, so actually I should remo= ve adding ->transferred from other filesystems. > > +=09=09spin_lock(&inode->i_lock); > > + > > +=09=09/* We can read the sizes directly as we hold i_lock. */ > > +=09=09i_size =3D inode->i_size; > Does reading and updating i_size from this asynchronous writeback path ra= ce > with concurrent truncate operations? Supposedly, you're not allowed to change i_size unless you hold i_lock... which we do. > Also, reading inode->i_size directly without i_size_read() bypasses > i_size_seqcount, which can cause torn reads on 32-bit platforms. Which should be irrelevant as we hold i_lock. David