Re: [PATCH -next] md: wake up mdmon after setting badblocks

[Mariusz Tkaczyk <mariusz.tkaczyk@xxxxxxxxxxxxxxx>]

On Thu,  1 Aug 2024 20:51:48 +0800
Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:

> From: Yu Kuai <yukuai3@xxxxxxxxxx>
> 
> For external super_block, mdmon rely on "mddev->sysfs_state" to update
> super_block. However, rdev_set_badblocks() will set sb_flags without
> waking up mdmon, which might cauing IO hang due to suepr_block can't be
> updated.
> 
> This problem is found by code review.
> 
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> ---
>  drivers/md/md.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 23cc77d51676..06d6ee8cd543 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -9831,10 +9831,12 @@ int rdev_set_badblocks(struct md_rdev *rdev, sector_t
> s, int sectors, /* Make sure they get written out promptly */
>  		if (test_bit(ExternalBbl, &rdev->flags))
>  			sysfs_notify_dirent_safe(rdev->sysfs_unack_badblocks);
> -		sysfs_notify_dirent_safe(rdev->sysfs_state);
>  		set_mask_bits(&mddev->sb_flags, 0,
>  			      BIT(MD_SB_CHANGE_CLEAN) |
> BIT(MD_SB_CHANGE_PENDING)); md_wakeup_thread(rdev->mddev->thread);
> +
> +		sysfs_notify_dirent_safe(rdev->sysfs_state);
> +		sysfs_notify_dirent_safe(mddev->sysfs_state);
>  		return 1;
>  	} else
>  		return 0;


Hey Kuai,
Later, I realized that mdmon is attached to various fds:

Here a mdmon code:

add_fd(&rfds, &maxfd, a->info.state_fd);	#mddev->sysfs_state
add_fd(&rfds, &maxfd, a->action_fd);		#mddev->sysfs_action
add_fd(&rfds, &maxfd, a->sync_completed_fd);	#mddev->resync_position


for (mdi = a->info.devs ; mdi ; mdi = mdi->next) { #for each rdev
	add_fd(&rfds, &maxfd, mdi->state_fd);		#rdev->sysfs_state
	add_fd(&rfds, &maxfd, mdi->bb_fd);		#rdev->sysfs_badblocks
	add_fd(&rfds, &maxfd, mdi->ubb_fd);
#rdev->sysfs_unack_badblocks }

Notification in rdev->sysfs_state is fine. The problem was somewhere else
(mdmon blocked on "rdev remove"). And It will be fixed by moving rdev remove to
managemon because it is blocking action now.

https://github.com/md-raid-utilities/mdadm/pull/66

I think it is fine to move this down after set_mask_bits, but we don't
have to repeat notification to mddev->state.

Thanks,
Mariusz