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 15CEBC433F5 for ; Wed, 20 Apr 2022 02:24:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348578AbiDTC1I (ORCPT ); Tue, 19 Apr 2022 22:27:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53138 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348564AbiDTC1H (ORCPT ); Tue, 19 Apr 2022 22:27:07 -0400 Received: from mout.gmx.net (mout.gmx.net [212.227.15.18]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AC3E12E9F6 for ; Tue, 19 Apr 2022 19:24:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1650421456; bh=xlxounuiEbpJhkvm5JyAVg67z6XK4C2NakOCV2Dhw1E=; h=X-UI-Sender-Class:Date:Subject:To:References:From:In-Reply-To; b=gtZ7zj93E1A0TdYp+lskVR/Kfa9IgiYA9W+bHfz9zojO6Z84gQ4WVAZ1Pe8D4Pikk NoXFglej3C44ukUMpLaUYo6Fjz+SxD8VLTowDc76FAmCfqA+4uV7rikI+Ol1coXx/v 5f7kBdDfmOZtcAP+H/vSyZzGRfqCnamjyWEp+1VY= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from [0.0.0.0] ([149.28.201.231]) by mail.gmx.net (mrgmx004 [212.227.17.184]) with ESMTPSA (Nemesis) id 1MkYXs-1oLEaP2vK2-00m0QL; Wed, 20 Apr 2022 04:24:16 +0200 Message-ID: Date: Wed, 20 Apr 2022 10:24:13 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH] btrfs: fix assertion failure during scrub due to block group reallocation Content-Language: en-US To: fdmanana@kernel.org, linux-btrfs@vger.kernel.org References: From: Qu Wenruo In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:F/RUhtSfp7xi22G0XeDSq2BiDp28aA+mA9//0tJ/cyymaRipZ4Y DY2zk6HxdQ0meZEHfNZkcP50wAaf5igGhd63Nc/W/jDM5ne8Y05RvlcYyFRHkSbeyCrGNuQ UuDbKeSEuDcWsuFreYqoi6+BwWbUvA/FPHuwKwgmOJInjuCmZf+a7x0T6U3AWGH8d50AgB+ 85sV27kNi9bzKvYLxiS2Q== X-UI-Out-Filterresults: notjunk:1;V03:K0:o6Bmv2WIrbA=:hHHs+eE1mNYtCGfrw9clVf RE7Qhun/IUm2DHN53CMsVfggqfuwE7HoEpDB85MbhTV0tUxGmoIpx0R2mEbXZBGLqi6CNfuAv 3s4pHDej1KccLguRftFqw5SF+WC89TvaAYEIeLVDV5Cs1rg+kC3IBi+rJzWbR6pKaKyusCpg5 Tau95Dm8dLY84PrQlv8BN4/FY0St0PDt/Cz6k6B3uyCmcgqgPJw/waimvhRQAcP7vJH8or1Xx C4tOppzNYVmwiIjZN5c9VFrpDspEPBydTHc293Rx6xdvrEdVRP58rIW4KM/yBvt058cBsof74 bEDA9Znj+PmhKK7fizVvQ4Z0CKTKcaUrg/jIpML4lAyHJk9y3OgiUvFl+vcn5u4irZsvRKhlZ Wf9+fUnwDfTOTIUUJ34SV8CNo3zLGa9Y0cTqthHMkGbISs6Wu8wjGVQhRQdlp+F2bvGYRvuqj u+8k0pY5vQEiT2+0OVkqbFrTZU4gC4/Z/56bBQNBrE6QFE5E46UnAtycZ4Js2YsF2iCI8g22A DZMs7GkvBGzecop9edfcEgUYHfz92m9Rs7pEYlkCIneATHqjxYbkmJkcMosm+f8us2GUpmN9w qtuv3w/NjXIa1KrO9qn5v1SI4RZdTW1VjtdjpmYf//c47KmcdGGRYuP1JZvn3xzgnkfJqR1IX e0fuo6E+I6yxHAyXrl153H+my8Gnz2Sa7aRoWFZv/cw3DzJRiTOCtEn3eC4SWW/uD8T/m7236 tSaMPT/JyJBa419r1bX5mAXEs82kK0GMoDtrkTN/46+MzxfyVU4+I6btC55Q69wBGIIW1jHie bbZgi2+jlk3szXRCKh4KUAyMB4xmzsjh/QCfisN8dWkX+PHmt+l5jqAoV9DzO4n4TyZwtuEKI h2lhgiX4oJprH79e0HzDB24yaepOpgGNHMmPPq5aDTY8R+dUMIiCy75jm7nYk5FuOTl+QN2DF B+JJA5aLNOq1wPGGvTc5bi4OYRiNV6rfqUewAiITcF2RMKNmHGD8IXgq27MQ6bxilc4JuKeR3 ErnFglzxMUzZl42WYHwhRXeI+eFiMQ2ylfQCwWsYrOqRMy/z06L3LMlUTAUHBvjKs9ETaMRt0 G8ctm6Q8AWk4hg= Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 2022/4/19 21:23, 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 =3D=3D 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-bt= rfs-next-114 #4 > [ 7526.390279] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BI= OS 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: 00000000= 00000000 > [ 7526.398732] RDX: 0000000000000000 RSI: ffffffff9d7239a2 RDI: 00000000= ffffffff > [ 7526.399766] RBP: ffffa0db8a911e10 R08: ffffffffa71a3ca0 R09: 00000000= 00000001 > [ 7526.400793] R10: 0000000000000001 R11: 0000000000000000 R12: ffffa0db= 4b170800 > [ 7526.401839] R13: 00000003494b0000 R14: ffffa0db7c55b488 R15: ffffa0db= 8b19a000 > [ 7526.402874] FS: 00007f6c99c40640(0000) GS:ffffa0de6d200000(0000) knl= GS:0000000000000000 > [ 7526.404038] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 7526.405040] CR2: 00007f31b0882160 CR3: 000000014b38c004 CR4: 00000000= 00370ee0 > [ 7526.406112] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 00000000= 00000000 > [ 7526.407148] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 00000000= 00000400 > [ 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: 000= 0000000000010 > [ 7526.420735] RAX: ffffffffffffffda RBX: 00005624e1e007b0 RCX: 00007f6c= 99d34397 > [ 7526.421779] RDX: 00005624e1e007b0 RSI: 00000000c400941b RDI: 00000000= 00000003 > [ 7526.422820] RBP: 0000000000000000 R08: 00007f6c99c40640 R09: 00000000= 00000000 > [ 7526.423906] R10: 00007f6c99c40640 R11: 0000000000000246 R12: 00007fff= 746755de > [ 7526.424924] R13: 00007fff746755df R14: 0000000000000000 R15: 00007f6c= 99c40640 > [ 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 cal= l > 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 mappin= g > red black tree (fs_info->mapping_tree), plus one. > > So we get a new block group that starts at logical address X and wit= h > a length of 1G. It spans over the whole logical range of the old blo= ck > 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 alloca= te > 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()= ; That perfectly explains the problem I hit. Thank you very much for further pin down the cause. > > 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 =3D=3D 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, becaus= e > 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 creat= ed > in the current transaction. It's pointless to continue and try to scrub > its extents, because scrub searches for extents using the commit root, s= o > 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 wri= te > duplication setup done through btrfs_map_block(). > > Signed-off-by: Filipe Manana The offending commit is relatively new, do we need to Cc to stable just for v5.17 kernel? Reviewed-by: Qu Wenruo Thanks, Qu > --- > fs/btrfs/dev-replace.c | 7 ++++++- > fs/btrfs/scrub.c | 26 +++++++++++++++++++++++++- > 2 files changed, 31 insertions(+), 2 deletions(-) > > diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c > index 677b99e66c21..a7dd6ba25e99 100644 > --- a/fs/btrfs/dev-replace.c > +++ b/fs/btrfs/dev-replace.c > @@ -707,7 +707,12 @@ static int btrfs_dev_replace_start(struct btrfs_fs_= info *fs_info, > > btrfs_wait_ordered_roots(fs_info, U64_MAX, 0, (u64)-1); > > - /* Commit dev_replace state and reserve 1 item for it. */ > + /* > + * Commit dev_replace state and reserve 1 item for it. > + * This is crucial to ensure we won't miss copying extents for new blo= ck > + * groups that are allocated after we started the device replace, and > + * must be done after setting up the device replace state. > + */ > trans =3D btrfs_start_transaction(root, 1); > if (IS_ERR(trans)) { > ret =3D PTR_ERR(trans); > diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c > index 13ba458c080c..b79a3221d7af 100644 > --- a/fs/btrfs/scrub.c > +++ b/fs/btrfs/scrub.c > @@ -3674,6 +3674,31 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx= , > if (!cache) > goto skip; > > + ASSERT(cache->start <=3D chunk_offset); > + /* > + * We are using the commit root to search for device extents, so > + * that means we could have found a device extent item from a > + * block group that was deleted in the current transaction. The > + * logical start offset of the deleted block group, stored at > + * @chunk_offset, might be part of the logical address range of > + * a new block group (which uses different physical extents). > + * In this case btrfs_lookup_block_group() has returned the new > + * block group, and its start address is less than @chunk_offset. > + * > + * We skip such new block groups, because it's pointless to > + * process them, as we won't find their extents because we search > + * for them using the commit root of the extent tree. For a device > + * replace it's also fine to skip it, we won't miss copying them > + * to the target device because we have the write duplication > + * setup through the regular write path (by btrfs_map_block()), > + * and we have committed a transaction when we started the device > + * replace, right after setting up the device replace state. > + */ > + if (cache->start < chunk_offset) { > + btrfs_put_block_group(cache); > + goto skip; > + } > + > if (sctx->is_dev_replace && btrfs_is_zoned(fs_info)) { > spin_lock(&cache->lock); > if (!cache->to_copy) { > @@ -3797,7 +3822,6 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx, > dev_replace->item_needs_writeback =3D 1; > up_write(&dev_replace->rwsem); > > - ASSERT(cache->start =3D=3D chunk_offset); > ret =3D scrub_chunk(sctx, cache, scrub_dev, found_key.offset, > dev_extent_len); >