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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20230608175031.9c534e7f554de89e3d972ab2@linux-foundation.org> References: <20230608175031.9c534e7f554de89e3d972ab2@linux-foundation.org> <20230607204120.89416-1-vishal.moola@gmail.com> <20230607204120.89416-2-vishal.moola@gmail.com> To: Andrew Morton Cc: dhowells@redhat.com, "Vishal Moola (Oracle)" , linux-afs@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] afs: Fix waiting for writeback then skipping folio MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <702178.1686955382.1@warthog.procyon.org.uk> Date: Fri, 16 Jun 2023 23:43:02 +0100 Message-ID: <702179.1686955382@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton wrote: > > Commit acc8d8588cb7 converted afs_writepages_region() to write back a > > folio batch. The function waits for writeback to a folio, but then > > proceeds to the rest of the batch without trying to write that folio > > again. This patch fixes has it attempt to write the folio again. > > > > This has only been compile tested. > > This seems fairly serious? We will try to write the again later, but sync()/fsync() might now have skipped it. > From my reading, we'll fail to write out the dirty data. Presumably > not easily observable, as it will get written out again later on. As it's a network filesystem, interactions with third parties could cause apparent corruption. Closing a file will flush it - but if there's a simultaneous op of some other kind, a bit of a flush or a sync may get missed and the copy visible to another user be temporarily missing that bit. > But we're also calling afs_write_back_from_locked_folio() with an unlocked > folio, which might cause mayhem. Without this patch, you mean? There's a "continue" statement that should send us back to the top of the loop before we get as far as afs_write_back_from_locked_folio() - and then the folio_unlock() there would go bang. David