xfs_scrub_all process execution results in a dead lock condition

[Patrick Fischer <patrick.fischer@siedl.net>]

Hello,
I've encountered a bug within the xfsprogs-dev utilities, particular within the Python script xfs_scrub_all.
I researched the master branch and saw, that the type of sub process call is like within kernel version 6.13.0-2 I stumbled across this issue.

Overview:
xfs_scrub_all.service systemd unit (or manual execution) is hanging due to a pipe buffer exhaustion after sub process call of lsblk.

Steps to reproduce:
Create a bunch of fake block devices to enlarge the output of lsblk to more than 65520 bytes:
> modprobe scsi_debug max_lunx=3 num_tgts=7 add_hosts=100


Run the command of xfs_scrub_all.service manually:
> /usr/sbin/xfs_scrub_all --auto-media-scan-interval 1mo


xfs_scrub_all shows a wait4 for the sub process lsblk:
> wait4(2148527,


Within sub process lsblk there is a write to FD1 / stdout:
> write(1, "                     {\n         "..., 4096


Affected Code in /usr/sbin/xfs_scrub_all[1]:
> 54     cmd=['lsblk', '-o', 'NAME,KNAME,TYPE,FSTYPE,MOUNTPOINT', '-J']
> 55     result = subprocess.Popen(cmd, stdout=subprocess.PIPE)
> 56     result.wait()
> 57     if result.returncode != 0:
> 58         return fs


Actual Results:
The execution of the command above launches a sub process of lsblk and returns more than 65520 bytes, resulting in an endless wait for return.

Expected Results:
The unit / process should not enter a dead lock.

[1] https://git.kernel.org/pub/scm/fs/xfs/xfsprogs-dev.git/tree/scrub/xfs_scrub_all.py.in

Regards,
Patrick Fischer

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