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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2B48EC433EF for ; Tue, 19 Apr 2022 18:06:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237722AbiDSSJQ (ORCPT ); Tue, 19 Apr 2022 14:09:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47202 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235918AbiDSSJO (ORCPT ); Tue, 19 Apr 2022 14:09:14 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 533F93C70D for ; Tue, 19 Apr 2022 11:06:30 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id F3CD2210F5; Tue, 19 Apr 2022 18:06:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1650391589; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=upvZjUNYW/8iWTRsRrbMazAb0v/bxm3vrB9/y/nroTk=; b=NyPOcHhe3MGflOSFiQ7uv0TZ00ShTXV0QuvvalktM4Mu6c5Edkq+DwsibpMiKexm/0jeyd FH2MLkjHd3FjKXhw5axOx1NTwIeh77XhPsGLbdSMvVEQ9D0HW7N3oWcnMMXJ+X0QwRadPk AGrP1y9Shi/18F2VVYDEgICDLnhFXzM= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1650391589; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=upvZjUNYW/8iWTRsRrbMazAb0v/bxm3vrB9/y/nroTk=; b=Tlwv5sC7dbEDXK1po41GpRq5qcbCqiqd4AVd6v3xBU7N8qJI7luK7kcS2IbuzIbUINc5+f ecVDozVi7b9XRiBA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id BB66B139BE; Tue, 19 Apr 2022 18:06:28 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id Wt+9LCT6XmKGdQAAMHmgww (envelope-from ); Tue, 19 Apr 2022 18:06:28 +0000 Date: Tue, 19 Apr 2022 20:02:25 +0200 From: David Sterba To: fdmanana@kernel.org Cc: linux-btrfs@vger.kernel.org Subject: Re: [PATCH] btrfs: fix assertion failure during scrub due to block group reallocation Message-ID: <20220419180225.GG2348@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, fdmanana@kernel.org, linux-btrfs@vger.kernel.org References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Tue, Apr 19, 2022 at 02:23:57PM +0100, fdmanana@kernel.org wrote: > From: Filipe Manana > > During a scrub, or device replace, we can race with block group removal > and allocation and trigger the following assertion failure: > > [ 7526.385524] assertion failed: cache->start == chunk_offset, in fs/btrfs/scrub.c:3817 > [ 7526.387351] ------------[ cut here ]------------ > [ 7526.387373] kernel BUG at fs/btrfs/ctree.h:3599! > [ 7526.388001] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC PTI > [ 7526.388970] CPU: 2 PID: 1158150 Comm: btrfs Not tainted 5.17.0-rc8-btrfs-next-114 #4 > [ 7526.390279] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 > [ 7526.392430] RIP: 0010:assertfail.constprop.0+0x18/0x1a [btrfs] > [ 7526.393520] Code: f3 48 c7 c7 20 (...) > [ 7526.396926] RSP: 0018:ffffb9154176bc40 EFLAGS: 00010246 > [ 7526.397690] RAX: 0000000000000048 RBX: ffffa0db8a910000 RCX: 0000000000000000 > [ 7526.398732] RDX: 0000000000000000 RSI: ffffffff9d7239a2 RDI: 00000000ffffffff > [ 7526.399766] RBP: ffffa0db8a911e10 R08: ffffffffa71a3ca0 R09: 0000000000000001 > [ 7526.400793] R10: 0000000000000001 R11: 0000000000000000 R12: ffffa0db4b170800 > [ 7526.401839] R13: 00000003494b0000 R14: ffffa0db7c55b488 R15: ffffa0db8b19a000 > [ 7526.402874] FS: 00007f6c99c40640(0000) GS:ffffa0de6d200000(0000) knlGS:0000000000000000 > [ 7526.404038] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 7526.405040] CR2: 00007f31b0882160 CR3: 000000014b38c004 CR4: 0000000000370ee0 > [ 7526.406112] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 7526.407148] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > [ 7526.408169] Call Trace: > [ 7526.408529] > [ 7526.408839] scrub_enumerate_chunks.cold+0x11/0x79 [btrfs] > [ 7526.409690] ? do_wait_intr_irq+0xb0/0xb0 > [ 7526.410276] btrfs_scrub_dev+0x226/0x620 [btrfs] > [ 7526.410995] ? preempt_count_add+0x49/0xa0 > [ 7526.411592] btrfs_ioctl+0x1ab5/0x36d0 [btrfs] > [ 7526.412278] ? __fget_files+0xc9/0x1b0 > [ 7526.412825] ? kvm_sched_clock_read+0x14/0x40 > [ 7526.413459] ? lock_release+0x155/0x4a0 > [ 7526.414022] ? __x64_sys_ioctl+0x83/0xb0 > [ 7526.414601] __x64_sys_ioctl+0x83/0xb0 > [ 7526.415150] do_syscall_64+0x3b/0xc0 > [ 7526.415675] entry_SYSCALL_64_after_hwframe+0x44/0xae > [ 7526.416408] RIP: 0033:0x7f6c99d34397 > [ 7526.416931] Code: 3c 1c e8 1c ff (...) > [ 7526.419641] RSP: 002b:00007f6c99c3fca8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 > [ 7526.420735] RAX: ffffffffffffffda RBX: 00005624e1e007b0 RCX: 00007f6c99d34397 > [ 7526.421779] RDX: 00005624e1e007b0 RSI: 00000000c400941b RDI: 0000000000000003 > [ 7526.422820] RBP: 0000000000000000 R08: 00007f6c99c40640 R09: 0000000000000000 > [ 7526.423906] R10: 00007f6c99c40640 R11: 0000000000000246 R12: 00007fff746755de > [ 7526.424924] R13: 00007fff746755df R14: 0000000000000000 R15: 00007f6c99c40640 > [ 7526.425950] > > That assertion is relatively new, introduced with commit d04fbe19aefd2 > ("btrfs: scrub: cleanup the argument list of scrub_chunk()"). > > The block group we get at scrub_enumerate_chunks() can actually have a > start address that is smaller then the chunk offset we extracted from a > device extent item we got from the commit root of the device tree. > This is very rare, but it can happen due to a race with block group > removal and allocation. For example, the following steps show how this > can happen: > > 1) We are at transaction T, and we have the following blocks groups, > sorted by their logical start address: > > [ bg A, start address A, length 1G (data) ] > [ bg B, start address B, length 1G (data) ] > (...) > [ bg W, start address W, length 1G (data) ] > > --> logical address space hole of 256M, > there used to be a 256M metadata block group here > > [ bg Y, start address Y, length 256M (metadata) ] > > --> Y matches W's end offset + 256M > > Block group Y is the block group with the highest logical address in > the whole filesystem; > > 2) Block group Y is deleted and its extent mapping is removed by the call > to remove_extent_mapping() made from btrfs_remove_block_group(). > > So after this point, the last element of the mapping red black tree, > its rightmost node, is the mapping for block group W; > > 3) While still at transaction T, a new data block group is allocated, > with a length of 1G. When creating the block group we do a call to > find_next_chunk(), which returns the logical start address for the > new block group. This calls returns X, which corresponds to the > end offset of the last block group, the rightmost node in the mapping > red black tree (fs_info->mapping_tree), plus one. > > So we get a new block group that starts at logical address X and with > a length of 1G. It spans over the whole logical range of the old block > group Y, that was previously removed in the same transaction. > > However the device extent allocated to block group X is not the same > device extent that was used by block group Y, and it also does not > overlap that extent, which must be always the case because we allocate > extents by searching through the commit root of the device tree > (otherwise it could corrupt a filesystem after a power failure or > an unclean shutdown in general), so the extent allocator is behaving > as expected; > > 4) We have a task running scrub, currently at scrub_enumerate_chunks(). > There it searches for device extent items in the device tree, using > its commit root. It finds a device extent item that was used by > block group Y, and it extracts the value Y from that item into the > local variable 'chunk_offset', using btrfs_dev_extent_chunk_offset(); > > It then calls btrfs_lookup_block_group() to find block group for > the logical address Y - since there's currently no block group that > starts at that logical address, it returns block group X, because > its range contains Y. > > This results in triggering the assertion: > > ASSERT(cache->start == chunk_offset); > > right before calling scrub_chunk(), as cache->start is X and > chunk_offset is Y. > > This is more likely to happen of filesystems not larger than 50G, because > for these filesystems we use a 256M size for metadata block groups and > a 1G size for data block groups, while for filesystems larger than 50G, > we use a 1G size for both data and metadata block groups (except for > zoned filesystems). It could also happen on any filesystem size due to > the fact that system block groups are always smaller (32M) than both > data and metadata block groups, but these are not frequently deleted, so > much less likely to trigger the race. > > So make scrub skip any block group with a start offset that is less than > the value we expect, as that means it's a new block group that was created > in the current transaction. It's pointless to continue and try to scrub > its extents, because scrub searches for extents using the commit root, so > it won't find any. For a device replace, skip it as well for the same > reasons, and we don't need to worry about the possibility of extents of > the new block group not being to the new device, because we have the write > duplication setup done through btrfs_map_block(). > > Signed-off-by: Filipe Manana Added to misc-next, thanks.