Re: [PATCH -next] md: split MD_RECOVERY_NEEDED out of mddev_resume

[Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>]

Hi,

在 2023/12/06 16:30, Song Liu 写道:
> On Sun, Dec 3, 2023 at 7:18 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > New mddev_resume() calls are added to synchroniza IO with array
> > reconfiguration, however, this introduce a regression while adding it in
> > md_start_sync():
> >
> > 1) someone set MD_RECOVERY_NEEDED first;
> > 2) daemon thread grab reconfig_mutex, then clear MD_RECOVERY_NEEDED and
> >     queue a new sync work;
> > 3) daemon thread release reconfig_mutex;
> > 4) in md_start_sync
> >     a) check that there are spares that can be added/removed, then suspend
> >        the array;
> >     b) remove_and_add_spares may not be called, or called without really
> >        add/remove spares;
> >     c) resume the array, then set MD_RECOVERY_NEEDED again!
> >
> > Loop between 2 - 4, then mddev_suspend() will be called quite often, for
> > consequence, normal IO will be quite slow.
> >
> > Fix this problem by spliting MD_RECOVERY_NEEDED out of mddev_resume(), so
> > that md_start_sync() won't set such flag and hence the loop will be broken.
>
> I hope we don't leak set_bit MD_RECOVERY_NEEDED to all call
> sites of mddev_resume().

There are also some other mddev_resume() that is added later and don't
need recovery, so md_start_sync() is not the only place:

 - md_setup_drive
 - rdev_attr_store
 - suspend_lo_store
 - suspend_hi_store
 - autorun_devices
 - md_ioct
 - r5c_disable_writeback_async
 - error path from new_dev_store(), ...

I'm not sure add a new helper is a good idea, because all above apis
should use new helper as well.

> How about something like the following instead?
>
> Please also incorporate feedback from Paul in the next version.

Of course.

Thanks,
Kuai

> Thanks,
> Song
>
> diff --git i/drivers/md/md.c w/drivers/md/md.c
> index c94373d64f2c..2d53e1b57070 100644
> --- i/drivers/md/md.c
> +++ w/drivers/md/md.c
> @@ -490,7 +490,7 @@ int mddev_suspend(struct mddev *mddev, bool interruptible)
>   }
>   EXPORT_SYMBOL_GPL(mddev_suspend);
>
> -void mddev_resume(struct mddev *mddev)
> +static void __mddev_resume(struct mddev *mddev, bool recovery_needed)
>   {
>          lockdep_assert_not_held(&mddev->reconfig_mutex);
>
> @@ -507,12 +507,18 @@ void mddev_resume(struct mddev *mddev)
>          percpu_ref_resurrect(&mddev->active_io);
>          wake_up(&mddev->sb_wait);
>
> -       set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
> +       if (recovery_needed)
> +               set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
>          md_wakeup_thread(mddev->thread);
>          md_wakeup_thread(mddev->sync_thread); /* possibly kick off a reshape */
>
>          mutex_unlock(&mddev->suspend_mutex);
>   }
> +
> +void mddev_resume(struct mddev *mddev)
> +{
> +       __mddev_resume(mddev, true);
> +}
>   EXPORT_SYMBOL_GPL(mddev_resume);
>
>   /*
> @@ -9403,7 +9409,9 @@ static void md_start_sync(struct work_struct *ws)
>                  goto not_running;
>          }
>
> -       suspend ? mddev_unlock_and_resume(mddev) : mddev_unlock(mddev);
> +       mddev_unlock(mddev);
> +       if (suspend)
> +               __mddev_resume(mddev, false);
>          md_wakeup_thread(mddev->sync_thread);
>          sysfs_notify_dirent_safe(mddev->sysfs_action);
>          md_new_event();
> @@ -9415,7 +9423,9 @@ static void md_start_sync(struct work_struct *ws)
>          clear_bit(MD_RECOVERY_REQUESTED, &mddev->recovery);
>          clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
>          clear_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
> -       suspend ? mddev_unlock_and_resume(mddev) : mddev_unlock(mddev);
> +       mddev_unlock(mddev);
> +       if (suspend)
> +               __mddev_resume(mddev, false);
>
>          wake_up(&resync_wait);
>          if (test_and_clear_bit(MD_RECOVERY_RECOVER, &mddev->recovery) &&
>
> .