From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 909C9C388F7 for ; Mon, 9 Nov 2020 13:08:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4E55C20731 for ; Mon, 9 Nov 2020 13:08:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604927313; bh=2h+ZNV3G4Q9jBLsnb1NkXvBXLZVyltoc1OW3nzC/sMQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=vBVrf2b1A+aTgedu1nthvbFqlgiNKNGJ0NHOUav0qnTzWy4A5AUuAy5+LntU/xgwy uxB25QHR5wlqswgPMedcJFPCTLuT3n4/E5boSQhfudx7OG65OYdONa6mJY+0GgRlcX VK/mcut2pOCpDEKXRvmagVoICohyiRhXjfIqdNrs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731673AbgKINIb (ORCPT ); Mon, 9 Nov 2020 08:08:31 -0500 Received: from mail.kernel.org ([198.145.29.99]:33254 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731658AbgKINI3 (ORCPT ); Mon, 9 Nov 2020 08:08:29 -0500 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8032520731; Mon, 9 Nov 2020 13:08:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604927308; bh=2h+ZNV3G4Q9jBLsnb1NkXvBXLZVyltoc1OW3nzC/sMQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tK0Xu3sfn9vVBr9hdIukyMK0q+rHcdd+12WmI544SYbMDotr/oq3slMPyM/sjZIZq 91WImaIK4I4lwI4Y+wcngN+kQF/MK48zjurbyRcWKBroRJFeQ4bQV/CNLQwelCSrbi fc3H7LgaSyb5BgbxtiZcpMBZTSecjI9kChW17tuU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Filipe Manana , Josef Bacik , David Sterba , Ben Hutchings Subject: [PATCH 4.19 16/71] btrfs: flush write bio if we loop in extent_write_cache_pages Date: Mon, 9 Nov 2020 13:55:10 +0100 Message-Id: <20201109125020.675443697@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201109125019.906191744@linuxfoundation.org> References: <20201109125019.906191744@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Josef Bacik commit 42ffb0bf584ae5b6b38f72259af1e0ee417ac77f upstream. There exists a deadlock with range_cyclic that has existed forever. If we loop around with a bio already built we could deadlock with a writer who has the page locked that we're attempting to write but is waiting on a page in our bio to be written out. The task traces are as follows PID: 1329874 TASK: ffff889ebcdf3800 CPU: 33 COMMAND: "kworker/u113:5" #0 [ffffc900297bb658] __schedule at ffffffff81a4c33f #1 [ffffc900297bb6e0] schedule at ffffffff81a4c6e3 #2 [ffffc900297bb6f8] io_schedule at ffffffff81a4ca42 #3 [ffffc900297bb708] __lock_page at ffffffff811f145b #4 [ffffc900297bb798] __process_pages_contig at ffffffff814bc502 #5 [ffffc900297bb8c8] lock_delalloc_pages at ffffffff814bc684 #6 [ffffc900297bb900] find_lock_delalloc_range at ffffffff814be9ff #7 [ffffc900297bb9a0] writepage_delalloc at ffffffff814bebd0 #8 [ffffc900297bba18] __extent_writepage at ffffffff814bfbf2 #9 [ffffc900297bba98] extent_write_cache_pages at ffffffff814bffbd PID: 2167901 TASK: ffff889dc6a59c00 CPU: 14 COMMAND: "aio-dio-invalid" #0 [ffffc9003b50bb18] __schedule at ffffffff81a4c33f #1 [ffffc9003b50bba0] schedule at ffffffff81a4c6e3 #2 [ffffc9003b50bbb8] io_schedule at ffffffff81a4ca42 #3 [ffffc9003b50bbc8] wait_on_page_bit at ffffffff811f24d6 #4 [ffffc9003b50bc60] prepare_pages at ffffffff814b05a7 #5 [ffffc9003b50bcd8] btrfs_buffered_write at ffffffff814b1359 #6 [ffffc9003b50bdb0] btrfs_file_write_iter at ffffffff814b5933 #7 [ffffc9003b50be38] new_sync_write at ffffffff8128f6a8 #8 [ffffc9003b50bec8] vfs_write at ffffffff81292b9d #9 [ffffc9003b50bf00] ksys_pwrite64 at ffffffff81293032 I used drgn to find the respective pages we were stuck on page_entry.page 0xffffea00fbfc7500 index 8148 bit 15 pid 2167901 page_entry.page 0xffffea00f9bb7400 index 7680 bit 0 pid 1329874 As you can see the kworker is waiting for bit 0 (PG_locked) on index 7680, and aio-dio-invalid is waiting for bit 15 (PG_writeback) on index 8148. aio-dio-invalid has 7680, and the kworker epd looks like the following crash> struct extent_page_data ffffc900297bbbb0 struct extent_page_data { bio = 0xffff889f747ed830, tree = 0xffff889eed6ba448, extent_locked = 0, sync_io = 0 } Probably worth mentioning as well that it waits for writeback of the page to complete while holding a lock on it (at prepare_pages()). Using drgn I walked the bio pages looking for page 0xffffea00fbfc7500 which is the one we're waiting for writeback on bio = Object(prog, 'struct bio', address=0xffff889f747ed830) for i in range(0, bio.bi_vcnt.value_()): bv = bio.bi_io_vec[i] if bv.bv_page.value_() == 0xffffea00fbfc7500: print("FOUND IT") which validated what I suspected. The fix for this is simple, flush the epd before we loop back around to the beginning of the file during writeout. Fixes: b293f02e1423 ("Btrfs: Add writepages support") CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Filipe Manana Signed-off-by: Josef Bacik Signed-off-by: David Sterba Signed-off-by: Ben Hutchings Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/extent_io.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -4045,7 +4045,16 @@ retry: */ scanned = 1; index = 0; - goto retry; + + /* + * If we're looping we could run into a page that is locked by a + * writer and that writer could be waiting on writeback for a + * page in our current bio, and thus deadlock, so flush the + * write bio here. + */ + ret = flush_write_bio(epd); + if (!ret) + goto retry; } if (wbc->range_cyclic || (wbc->nr_to_write > 0 && range_whole))