[BUG] During the development to make btrfs pass generic/563 (which needs to make btrfs to support partial updaote folios), generic/095 causes hangs during tests. The call trace for the hanging process looks like this: __switch_to+0xf8/0x168 __schedule+0x328/0x8a8 schedule+0x54/0x140 io_schedule+0x44/0x68 folio_wait_bit_common+0x198/0x3f8 __folio_lock+0x24/0x40 extent_write_cache_pages+0x2e0/0x4c0 [btrfs] btrfs_writepages+0x94/0x158 [btrfs] do_writepages+0x74/0x190 filemap_fdatawrite_wbc+0x88/0xc8 __filemap_fdatawrite_range+0x6c/0xa8 filemap_fdatawrite_range+0x1c/0x30 btrfs_start_ordered_extent+0x264/0x2e0 [btrfs] btrfs_lock_and_flush_ordered_range+0x8c/0x160 [btrfs] __get_extent_map+0xa0/0x220 [btrfs] btrfs_do_readpage+0x1bc/0x5d8 [btrfs] btrfs_read_folio+0x50/0xa0 [btrfs] filemap_read_folio+0x54/0x110 filemap_update_page+0x2e0/0x3b8 filemap_get_pages+0x228/0x4d8 filemap_read+0x11c/0x3b8 btrfs_file_read_iter+0x74/0x90 [btrfs] new_sync_read+0xd0/0x1d0 vfs_read+0x1a0/0x1f0 [CAUSE] The root cause is a btrfs specific behavior that during a folio read, we can trigger writeback of the same folio, which will try to lock the same folio already locked by the read process. The fix is already sent to the mailing list: https://lore.kernel.org/linux-btrfs/62bf73ada7be2888d45a787c2b6fd252103a5d25.1729725088.git.wqu@xxxxxxxx/ This problem can only happen if all the following conditions are met: - The sector size of btrfs is smaller than page size To have partial uptodate folios. - Btrfs won't read the full folio if buffered write is block aligned This is done by the not yet merged patch: https://lore.kernel.org/linux-btrfs/ac2639ec4e9ac176d33e95ef7ecf008fa6be5461.1727833878.git.wqu@xxxxxxxx/ [TEST CASE] During the debugging of that generic/095 hang, I extracted a minimal reproducer which is much smaller and faster, although it still requires several runs to trigger a hang. The test case will run the fio workload 32 times by default, which is more than enough to trigger the hang. Signed-off-by: Qu Wenruo <wqu@xxxxxxxx> --- tests/generic/366 | 80 +++++++++++++++++++++++++++++++++++++++++++ tests/generic/366.out | 2 ++ 2 files changed, 82 insertions(+) create mode 100755 tests/generic/366 create mode 100644 tests/generic/366.out diff --git a/tests/generic/366 b/tests/generic/366 new file mode 100755 index 00000000..2ebc5728 --- /dev/null +++ b/tests/generic/366 @@ -0,0 +1,80 @@ +#! /bin/bash +# SPDX-License-Identifier: GPL-2.0 +# Copyright (C) 2024 SUSE Linux Products GmbH. All Rights Reserved. +# +# FS QA Test 366 +# +# Test if certain fio load will hang the filesystem. +# +# This is exposed by an incoming btrfs feature, which allows a folio to be +# partial uptodate if the buffered write range is block aligned but not yet +# full folio aligned. +# +# Such behavior makes btrfs to hang reliably under generic/095. +# This is the extracted minimal reproducer for 4k block size and 64K page size. +# +. ./common/preamble +_begin_fstest auto quick + +. ./common/filter + +_require_scratch +_require_odirect +_require_aio + +_fixed_by_kernel_commit fa630df665aa \ +_fixed_by_kernel_commit xxxxxxxxxxxx \ + "btrfs: avoid deadlock when reading a partial uptodate folio" + +iterations=$((32 * LOAD_FACTOR)) + +fio_config=$tmp.fio +fio_out=$tmp.fio.out +blksz=`$here/src/min_dio_alignment $SCRATCH_MNT $SCRATCH_DEV` +cat >$fio_config <<EOF +[global] +bs=8k +iodepth=1 +randrepeat=1 +size=256k +directory=$SCRATCH_MNT +numjobs=1 +[job1] +ioengine=sync +bs=512 +direct=1 +rw=randread +filename=file1 +[job2] +ioengine=libaio +rw=randwrite +direct=1 +filename=file1 +[job3] +ioengine=posixaio +rw=randwrite +filename=file1 +EOF +_require_fio $fio_config + +for (( i = 0; i < $iterations; i++)); do + _scratch_mkfs >>$seqres.full 2>&1 + _scratch_mount + # There's a known EIO failure to report collisions between directio and buffered + # writes to userspace, refer to upstream linux 5a9d929d6e13. So ignore EIO error + # at here. + $FIO_PROG $fio_config --ignore_error=,EIO --output=$fio_out + # umount before checking dmesg in case umount triggers any WARNING or Oops + _scratch_unmount + + _check_dmesg _filter_aiodio_dmesg + + echo "=== fio $i/$iterations ===" >> $seqres.full + cat $fio_out >> $seqres.full +done + +echo "Silence is golden" + +# success, all done +status=0 +exit diff --git a/tests/generic/366.out b/tests/generic/366.out new file mode 100644 index 00000000..1fe90e06 --- /dev/null +++ b/tests/generic/366.out @@ -0,0 +1,2 @@ +QA output created by 366 +Silence is golden -- 2.46.0
