Re: [PATCH 1/6] common: udev settle before _scratch_pool_mkfs

[Anand Jain <anand.jain@oracle.com>]

On 5/17/24 06:12, David Sterba wrote:
> From: Josef Bacik <josef@toxicpanda.com>
> 
> There are some btrfs tests that do _scratch_pool_mkfs in a loop.
> Sometimes this fails with EBUSY.  Tracing revealed that udevd will
> sometimes write to /sys/block/device/uevent to make sure an event
> triggers to rules get written.  However these events will not get sent
> to user space until after an O_EXCL open as been closed.  The general
> flow is something like
> 
> mkfs.btrfs /dev/sda /dev/sdb /dev/sdc /dev/sdd
> mount /dev/sda /mnt/test
> <things>
> umount /mnt/test
> 
> in a loop.  The problem is udevd will add uevents for the devices and
> they won't get delivered until after the umount.  If we're doing the
> above sequence in a loop the next mkfs.btrfs will fail because udev is
> touching the devices to consume the KOBJ_CHANGE event.
> 
> Fix this by doing a udev settle before _scratch_pool_mkfs.
> 



> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> Signed-off-by: David Sterba <dsterba@suse.com>
> ---
>   common/rc | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/common/rc b/common/rc
> index 0fe56382a6a497..5d38571ffe87eb 100644
> --- a/common/rc
> +++ b/common/rc
> @@ -903,6 +903,12 @@ _scratch_pool_mkfs()
>   {
>       case $FSTYP in
>       btrfs)
> +	# For multi-disk file systems udev can queue up events on the device
> +	# when we mkfs the device, and thus tie up the device after we've
> +	# unmounted.  Tests that _scratch_pool_mkfs() in a loop can sometimes
> +	# trip over udev trying to do the updates after the umount, so make sure
> +	# we settle before we try mkfs'ing so we don't get an EBUSY
> +	$UDEV_SETTLE_PROG >/dev/null 2>&1
>           $MKFS_BTRFS_PROG $MKFS_OPTIONS $* $SCRATCH_DEV_POOL > /dev/null
>           ;;


Just curious: have we seen this issue even after the btrfs-progs commit 
below?

   e54514aaeab6 btrfs-progs: fix stray fd close in open_ctree_fs_info()

Thanks, Anand

>       *)