Re: [PATCH] fstests: btrfs: add a new test case for fstrim crash

On Tue, Jun 2, 2026 at 5:34 AM Qu Wenruo <[email protected]> wrote:
>
> There is a bug report that btrfs/242 can crash very randomly.
>
> It turns out the crash is caused by a re-appearing missing device, which
> screwed up several checks in fstrim.
>
> This new test case is a more reliable version, dedicated for such crash,
> which will:
>
> - Create a raid1 btrfs
> - Mount with a single device in degraded mode
> - Let the missing device to re-appear
> - Run fstrim
>
> Which is reliably crashing in my environment without the submitted fix.
> And with the submitted fix, the test no longer crashes.
>
> Reported-by: Su Yue <[email protected]>
> Link: https://lore.kernel.org/linux-btrfs/[email protected]/
> Signed-off-by: Qu Wenruo <[email protected]>
> ---
>  tests/btrfs/350     | 38 ++++++++++++++++++++++++++++++++++++++
>  tests/btrfs/350.out |  2 ++
>  2 files changed, 40 insertions(+)
>  create mode 100755 tests/btrfs/350
>  create mode 100644 tests/btrfs/350.out
>
> diff --git a/tests/btrfs/350 b/tests/btrfs/350
> new file mode 100755
> index 00000000..1206d66f
> --- /dev/null
> +++ b/tests/btrfs/350
> @@ -0,0 +1,38 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2026 SUSE S.A.  All Rights Reserved.
> +#
> +# FS QA Test 350
> +#
> +# Make sure fstrim will not crash when a missing device re-appeared.
> +#
> +. ./common/preamble
> +_begin_fstest auto quick volume trim raid
> +
> +_fixed_by_kernel_commit XXXXXXXXXXXX \
> +       "btrfs: do not trim a device which is not writeable"
> +
> +_require_btrfs_forget_or_module_loadable
> +_require_scratch_dev_pool 2
> +_scratch_dev_pool_get 2
> +dev1=$(echo $SCRATCH_DEV_POOL | $AWK_PROG '{ print $1 }')
> +dev2=$(echo $SCRATCH_DEV_POOL | $AWK_PROG '{ print $2 }')
> +
> +_scratch_pool_mkfs "-m raid1 -d raid1"
> +_require_batched_discard $SCRATCH_MNT
> +
> +# Mount the filesystem in degraded mode
> +_btrfs_forget_or_module_reload
> +_mount -o degraded $dev1 $SCRATCH_MNT
> +
> +# Now let devid 2 reappear
> +_btrfs device scan $dev2
> +
> +# Run fstrim, it should skip the re-appeared device, as it still
> +# lacks WRITEBALE flag nor a proper bdev pointer.

nor -> and

> +#
> +# For unpatched kernel, it will crash with a NULL pointer dereference.
> +$FSTRIM_PROG $SCRATCH_MNT

Misses a call to:   _scratch_dev_pool_put

Otherwise:

Reviewed-by: Filipe Manana <[email protected]>

Thanks.

> +
> +echo "Silence is golden"
> +_exit 0
> diff --git a/tests/btrfs/350.out b/tests/btrfs/350.out
> new file mode 100644
> index 00000000..e9aad823
> --- /dev/null
> +++ b/tests/btrfs/350.out
> @@ -0,0 +1,2 @@
> +QA output created by 350
> +Silence is golden
> --
> 2.51.2
>
>