linux-kernel - [BUG] btrfs potential failure on 32 core LTP test (fallocate05)

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Date:   Tue, 29 Jun 2021 19:00:28 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "kernel-team@...ts.ubuntu.com" <kernel-team@...ts.ubuntu.com>,
        "ltp@...ts.linux.it" <ltp@...ts.linux.it>,
        Qu Wenruo <wqu@...e.com>, Filipe Manana <fdmanana@...e.com>
Subject: [BUG] btrfs potential failure on 32 core LTP test (fallocate05)

Dear BTRFS folks,

I am hitting a potential regression of btrfs, visible only with
fallocate05 test from LTP (Linux Test Project) only on 32+ core Azure
instances (x86_64).

Tested:
v5.8 (Ubuntu with our stable patches): PASS
v5.11 (Ubuntu with our stable patches): FAIL
v5.13 mainline: FAIL

PASS means test passes on all instances
FAIL means test passes on other instance types (e.g. 4 or 16 core) but
fails on 32 and 64 core instances (did not test higher),
e.g.: Standard_F32s_v2, Standard_F64s_v2, Standard_D32s_v3,
Standard_E32s_v3

Reproduction steps:
git clone https://github.com/linux-test-project/ltp.git
cd ltp
./build.sh && make install -j8
cd ../ltp-install
sudo ./runltp -f syscalls -s fallocate05

Failure output:
tst_test.c:1379: TINFO: Testing on btrfs
tst_test.c:888: TINFO: Formatting /dev/loop4 with btrfs opts='' extra opts=''
tst_test.c:1311: TINFO: Timeout per run is 0h 05m 00s
tst_fill_fs.c:32: TINFO: Creating file mntpoint/file0 size 21710183
tst_fill_fs.c:32: TINFO: Creating file mntpoint/file1 size 8070086
tst_fill_fs.c:32: TINFO: Creating file mntpoint/file2 size 3971177
tst_fill_fs.c:32: TINFO: Creating file mntpoint/file3 size 36915315
tst_fill_fs.c:32: TINFO: Creating file mntpoint/file4 size 70310993
tst_fill_fs.c:32: TINFO: Creating file mntpoint/file5 size 4807935
tst_fill_fs.c:32: TINFO: Creating file mntpoint/file6 size 90739786
tst_fill_fs.c:32: TINFO: Creating file mntpoint/file7 size 76896492
tst_fill_fs.c:32: TINFO: Creating file mntpoint/file8 size 72228649
tst_fill_fs.c:32: TINFO: Creating file mntpoint/file9 size 36207821
tst_fill_fs.c:32: TINFO: Creating file mntpoint/file10 size 81483962
tst_fill_fs.c:59: TINFO: write(): ENOSPC (28)
fallocate05.c:81: TPASS: write() wrote 65536 bytes
fallocate05.c:102: TINFO: fallocate()d 0 extra blocks on full FS
fallocate05.c:114: TPASS: fallocate() on full FS
fallocate05.c:130: TPASS: fallocate(FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE)
fallocate05.c:134: TFAIL: write(): ENOSPC (28)

Test code:
https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/fallocate/fallocate05.c#L134

See also: https://bugs.launchpad.net/ubuntu-kernel-tests/+bug/1933112

Other FS tests succeed on that machines/kernels. Other file systems
also pass - only btrfs fails. The issue was not bisected. Full test
log attached.

Best regards,
Krzysztof

View attachment "32-core-btrfs-fail-log.txt" of type "text/plain" (105692 bytes)