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Registered in England and Wales under Company Registration No. 3798903 From: David Howells To: torvalds@linux-foundation.org cc: dhowells@redhat.com, Dave Wysochanski , Jeff Layton , linux-cachefs@redhat.com, linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] netfs: Only call folio_start_fscache() one time for each folio MIME-Version: 1.0 Content-ID: <3993456.1695043031.1@warthog.procyon.org.uk> Date: Mon, 18 Sep 2023 14:17:11 +0100 Message-ID: <3993457.1695043031@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Spam-Status: No, score=-0.9 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on morse.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (morse.vger.email [0.0.0.0]); Mon, 18 Sep 2023 08:25:21 -0700 (PDT) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1777409687830677214 X-GMAIL-MSGID: 1777409687830677214 Hi Linus, Could you apply this please? Thanks, David --- From: Dave Wysochanski If a network filesystem using netfs implements a clamp_length() function, it can set subrequest lengths smaller than a page size. When we loop through the folios in netfs_rreq_unlock_folios() to set any folios to be written back, we need to make sure we only call folio_start_fscache() once for each folio. Otherwise, this simple testcase: mount -o fsc,rsize=1024,wsize=1024 127.0.0.1:/export /mnt/nfs dd if=/dev/zero of=/mnt/nfs/file.bin bs=4096 count=1 1+0 records in 1+0 records out 4096 bytes (4.1 kB, 4.0 KiB) copied, 0.0126359 s, 324 kB/s echo 3 > /proc/sys/vm/drop_caches cat /mnt/nfs/file.bin > /dev/null will trigger an oops similar to the following: ... page dumped because: VM_BUG_ON_FOLIO(folio_test_private_2(folio)) ------------[ cut here ]------------ kernel BUG at include/linux/netfs.h:44! ... CPU: 5 PID: 134 Comm: kworker/u16:5 Kdump: loaded Not tainted 6.4.0-rc5 ... RIP: 0010:netfs_rreq_unlock_folios+0x68e/0x730 [netfs] ... Call Trace: netfs_rreq_assess+0x497/0x660 [netfs] netfs_subreq_terminated+0x32b/0x610 [netfs] nfs_netfs_read_completion+0x14e/0x1a0 [nfs] nfs_read_completion+0x2f9/0x330 [nfs] rpc_free_task+0x72/0xa0 [sunrpc] rpc_async_release+0x46/0x70 [sunrpc] process_one_work+0x3bd/0x710 worker_thread+0x89/0x610 kthread+0x181/0x1c0 ret_from_fork+0x29/0x50 Fixes: 3d3c95046742 ("netfs: Provide readahead and readpage netfs helpers" Link: https://bugzilla.redhat.com/show_bug.cgi?id=2210612 Signed-off-by: Dave Wysochanski Reviewed-by: Jeff Layton Signed-off-by: David Howells Link: https://lore.kernel.org/r/20230608214137.856006-1-dwysocha@redhat.com/ # v1 Link: https://lore.kernel.org/r/20230915185704.1082982-1-dwysocha@redhat.com/ # v2 --- fs/netfs/buffered_read.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c index 3404707ddbe7..2cd3ccf4c439 100644 --- a/fs/netfs/buffered_read.c +++ b/fs/netfs/buffered_read.c @@ -47,12 +47,14 @@ void netfs_rreq_unlock_folios(struct netfs_io_request *rreq) xas_for_each(&xas, folio, last_page) { loff_t pg_end; bool pg_failed = false; + bool folio_started; if (xas_retry(&xas, folio)) continue; pg_end = folio_pos(folio) + folio_size(folio) - 1; + folio_started = false; for (;;) { loff_t sreq_end; @@ -60,8 +62,10 @@ void netfs_rreq_unlock_folios(struct netfs_io_request *rreq) pg_failed = true; break; } - if (test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags)) + if (!folio_started && test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags)) { folio_start_fscache(folio); + folio_started = true; + } pg_failed |= subreq_failed; sreq_end = subreq->start + subreq->len - 1; if (pg_end < sreq_end)