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[2403:580d:fda1::299]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b5faa2df0asm182394675ad.26.2026.04.22.22.00.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 22 Apr 2026 22:00:15 -0700 (PDT) Message-ID: Date: Thu, 23 Apr 2026 14:30:11 +0930 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] btrfs: preallocate extent changeset before acquiring extent_io_tree lock To: tchou , linux-btrfs@vger.kernel.org Cc: clm@fb.com, dsterba@suse.com, quwenruo.btrfs@gmx.com References: <20260417064011.1316310-1-tchou@synology.com> <20260417073836.1320467-1-tchou@synology.com> Content-Language: en-US From: Qu Wenruo Autocrypt: addr=wqu@suse.com; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAHNGFF1IFdlbnJ1byA8d3F1QHN1c2UuY29tPsLAlAQTAQgAPgIbAwULCQgHAgYVCAkKCwIE FgIDAQIeAQIXgBYhBC3fcuWlpVuonapC4cI9kfOhJf6oBQJnEXVgBQkQ/lqxAAoJEMI9kfOh Jf6o+jIH/2KhFmyOw4XWAYbnnijuYqb/obGae8HhcJO2KIGcxbsinK+KQFTSZnkFxnbsQ+VY fvtWBHGt8WfHcNmfjdejmy9si2jyy8smQV2jiB60a8iqQXGmsrkuR+AM2V360oEbMF3gVvim 2VSX2IiW9KERuhifjseNV1HLk0SHw5NnXiWh1THTqtvFFY+CwnLN2GqiMaSLF6gATW05/sEd V17MdI1z4+WSk7D57FlLjp50F3ow2WJtXwG8yG8d6S40dytZpH9iFuk12Sbg7lrtQxPPOIEU rpmZLfCNJJoZj603613w/M8EiZw6MohzikTWcFc55RLYJPBWQ+9puZtx1DopW2jOwE0EWdWB rwEIAKpT62HgSzL9zwGe+WIUCMB+nOEjXAfvoUPUwk+YCEDcOdfkkM5FyBoJs8TCEuPXGXBO Cl5P5B8OYYnkHkGWutAVlUTV8KESOIm/KJIA7jJA+Ss9VhMjtePfgWexw+P8itFRSRrrwyUf E+0WcAevblUi45LjWWZgpg3A80tHP0iToOZ5MbdYk7YFBE29cDSleskfV80ZKxFv6koQocq0 vXzTfHvXNDELAuH7Ms/WJcdUzmPyBf3Oq6mKBBH8J6XZc9LjjNZwNbyvsHSrV5bgmu/THX2n g/3be+iqf6OggCiy3I1NSMJ5KtR0q2H2Nx2Vqb1fYPOID8McMV9Ll6rh8S8AEQEAAcLAfAQY AQgAJgIbDBYhBC3fcuWlpVuonapC4cI9kfOhJf6oBQJnEXWBBQkQ/lrSAAoJEMI9kfOhJf6o cakH+QHwDszsoYvmrNq36MFGgvAHRjdlrHRBa4A1V1kzd4kOUokongcrOOgHY9yfglcvZqlJ qfa4l+1oxs1BvCi29psteQTtw+memmcGruKi+YHD7793zNCMtAtYidDmQ2pWaLfqSaryjlzR /3tBWMyvIeWZKURnZbBzWRREB7iWxEbZ014B3gICqZPDRwwitHpH8Om3eZr7ygZck6bBa4MU o1XgbZcspyCGqu1xF/bMAY2iCDcq6ULKQceuKkbeQ8qxvt9hVxJC2W3lHq8dlK1pkHPDg9wO JoAXek8MF37R8gpLoGWl41FIUb3hFiu3zhDDvslYM4BmzI18QgQTQnotJH8= In-Reply-To: <20260417073836.1320467-1-tchou@synology.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2026/4/17 17:08, tchou 写道: > In btrfs_clear_extent_bit_changeset(), the extent changeset ulist may need > to allocate new nodes. Currently, this can happen while holding the > extent_io_tree->lock spinlock. Although ulist_prealloc() uses GFP_NOFS to > avoid deadlock with filesystem reclaim, it's better to preallocate before > acquiring the spinlock to: > > 1. Avoid potential allocation failures while holding the lock > 2. Be consistent with set_extent_bit() which already preallocates both > extent state and changeset before the spinlock > 3. Reduce lock contention by not doing allocations under the lock > > Preallocate the changeset ulist node before acquiring the spinlock, > mirroring the pattern used for extent state preallocation. > > Signed-off-by: Ting-Chang Hou > Reviewed-by: Qu Wenruo > --- This patch cause reliable ASSERT() triggering in btrfs/022, with the following call trace: [ 65.405567] BTRFS info (device dm-3): qgroup scan completed (inconsistency flag cleared) [ 65.644601] assertion failed: extent_changeset_tracks_ranges(changeset), in extent_io.h:234 [ 65.646833] ------------[ cut here ]------------ [ 65.648119] kernel BUG at extent_io.h:234! [ 65.649323] Oops: invalid opcode: 0000 [#1] SMP [ 65.651134] CPU: 9 UID: 0 PID: 76 Comm: kworker/u50:0 Tainted: G OE 7.0.0-rc7-custom+ #366 PREEMPT(full) e43575492b73961c1dd795487d0d2ceacbfdec38 [ 65.654784] Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE [ 65.656170] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS unknown 02/02/2022 [ 65.658210] Workqueue: btrfs-flush_delalloc btrfs_work_helper [btrfs] [ 65.659988] RIP: 0010:extent_changeset_prealloc.part.0+0x1f/0x21 [btrfs] [ 65.661798] Code: 0f 0b 66 0f 1f 84 00 00 00 00 00 b9 ea 00 00 00 48 c7 c2 b2 2a 8f c0 48 c7 c6 88 92 90 c0 48 c7 c7 b8 92 90 c0 e8 a1 67 2e d1 <0f> 0b 48 c7 c6 c0 b0 82 c0 48 89 0c 24 e8 cf 92 30 d1 48 8b 0c 24 [ 65.666489] RSP: 0018:ffffccbbc0aeb680 EFLAGS: 00010246 [ 65.667835] RAX: 000000000000004f RBX: 00000000004bffff RCX: 0000000000000000 [ 65.669660] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8aea77c9d3c0 [ 65.671483] RBP: 0000000000001000 R08: 0000000000000000 R09: 00000000ffffefff [ 65.673317] R10: ffffffff93a59b00 R11: ffffccbbc0aeb520 R12: ffff8ae9151f6c30 [ 65.675209] R13: 0000000000000000 R14: 00000000004c0000 R15: 00000000004bffff [ 65.677076] FS: 0000000000000000(0000) GS:ffff8aeae385b000(0000) knlGS:0000000000000000 [ 65.679132] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 65.680624] CR2: 00007f1afd800000 CR3: 0000000151124000 CR4: 0000000000750ef0 [ 65.682507] PKRU: 55555554 [ 65.683259] Call Trace: [ 65.683939] [ 65.684525] btrfs_clear_extent_bit_changeset.cold+0x109/0x14c [btrfs 344d2e6beaedee2ce747d6035131ee8e936844c5] [ 65.687187] __btrfs_qgroup_release_data+0xa2/0x1f0 [btrfs 344d2e6beaedee2ce747d6035131ee8e936844c5] [ 65.689565] alloc_ordered_extent+0x266/0x330 [btrfs 344d2e6beaedee2ce747d6035131ee8e936844c5] [ 65.691840] btrfs_alloc_ordered_extent+0x290/0x350 [btrfs 344d2e6beaedee2ce747d6035131ee8e936844c5] [ 65.694245] cow_file_range+0x226/0x8a0 [btrfs 344d2e6beaedee2ce747d6035131ee8e936844c5] [ 65.696388] writepage_delalloc+0x35b/0x6e0 [btrfs 344d2e6beaedee2ce747d6035131ee8e936844c5] [ 65.698636] extent_write_cache_pages+0x25f/0x820 [btrfs 344d2e6beaedee2ce747d6035131ee8e936844c5] [ 65.701004] ? __ext4_journal_get_write_access+0x53/0x160 [ext4 69c3e1469031ed506d5e673d78e2ebe810d3edeb] [ 65.703527] btrfs_writepages+0x74/0x130 [btrfs 344d2e6beaedee2ce747d6035131ee8e936844c5] [ 65.705705] do_writepages+0xd0/0x160 [ 65.706729] ? _raw_spin_unlock+0xe/0x20 [ 65.707785] ? wbc_attach_and_unlock_inode+0xd1/0x130 [ 65.709133] filemap_writeback+0xb5/0xe0 [ 65.710192] btrfs_run_delalloc_work+0x1b/0x50 [btrfs 344d2e6beaedee2ce747d6035131ee8e936844c5] [ 65.712508] btrfs_work_helper+0xd7/0x3b0 [btrfs 344d2e6beaedee2ce747d6035131ee8e936844c5] [ 65.714708] process_one_work+0x198/0x3b0 [ 65.715771] worker_thread+0x1c8/0x330 [ 65.716929] ? rescuer_thread+0x5d0/0x5d0 [ 65.718038] kthread+0xee/0x120 [ 65.718877] ? kthreads_online_cpu+0x10/0x10 [ 65.719998] ret_from_fork+0x2a6/0x330 [ 65.720987] ? kthreads_online_cpu+0x10/0x10 [ 65.722143] ret_from_fork_asm+0x11/0x20 [ 65.723180] Next time please run a full fstests run, with CONFIG_BTRFS_ASSERT, CONFIG_BTRFS_DEBUG and CONFIG_BTRFS_EXPERIMENTAL enabled. Now removed from for-next branch. Thanks, Qu > fs/btrfs/extent-io-tree.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/fs/btrfs/extent-io-tree.c b/fs/btrfs/extent-io-tree.c > index 626702244809..b5ba650cdb55 100644 > --- a/fs/btrfs/extent-io-tree.c > +++ b/fs/btrfs/extent-io-tree.c > @@ -663,6 +663,9 @@ int btrfs_clear_extent_bit_changeset(struct extent_io_tree *tree, u64 start, u64 > */ > prealloc = alloc_extent_state(mask); > } > + /* Preallocate the extent changeset ulist node before acquiring spinlock. */ > + if (changeset) > + extent_changeset_prealloc(changeset, mask); > > spin_lock(&tree->lock); > if (cached_state) {