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Message-ID: <CALTww2-5F=C5N6YZ-3weD9xSWhpT6Mx8NkaevfXZWqR6=Bwc4A@mail.gmail.com>
Date: Mon, 25 Sep 2023 15:21:45 +0800
From: Xiao Ni <xni@...hat.com>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: agk@...hat.com, snitzer@...nel.org, dm-devel@...hat.com,
song@...nel.org, linux-kernel@...r.kernel.org,
linux-raid@...r.kernel.org, yukuai3@...wei.com,
yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH -next v2 03/28] md: add new helpers to suspend/resume array
On Mon, Aug 28, 2023 at 10:04 AM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@...wei.com>
>
> Advantages for new apis:
> - reconfig_mutex is not required;
> - the weird logical that suspend array hold 'reconfig_mutex' for
> mddev_check_recovery() to update superblock is not needed;
> - the specail handling, 'pers->prepare_suspend', for raid456 is not
> needed;
> - It's safe to be called at any time once mddev is allocated, and it's
> designed to be used from slow path where array configuration is changed;
>
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
> drivers/md/md.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++--
> drivers/md/md.h | 3 ++
> 2 files changed, 86 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 7fa311a14317..6236e2e395c1 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -443,12 +443,22 @@ void mddev_suspend(struct mddev *mddev)
> lockdep_is_held(&mddev->reconfig_mutex));
>
> WARN_ON_ONCE(thread && current == thread->tsk);
> - if (mddev->suspended++)
> +
> + /* can't concurrent with __mddev_suspend() and __mddev_resume() */
> + mutex_lock(&mddev->suspend_mutex);
> + if (mddev->suspended++) {
> + mutex_unlock(&mddev->suspend_mutex);
> return;
> + }
> +
> wake_up(&mddev->sb_wait);
> set_bit(MD_ALLOW_SB_UPDATE, &mddev->flags);
> percpu_ref_kill(&mddev->active_io);
>
> + /*
> + * TODO: cleanup 'pers->prepare_suspend after all callers are replaced
> + * by __mddev_suspend().
> + */
> if (mddev->pers && mddev->pers->prepare_suspend)
> mddev->pers->prepare_suspend(mddev);
>
> @@ -459,14 +469,21 @@ void mddev_suspend(struct mddev *mddev)
> del_timer_sync(&mddev->safemode_timer);
> /* restrict memory reclaim I/O during raid array is suspend */
> mddev->noio_flag = memalloc_noio_save();
> +
> + mutex_unlock(&mddev->suspend_mutex);
> }
> EXPORT_SYMBOL_GPL(mddev_suspend);
>
> void mddev_resume(struct mddev *mddev)
> {
> lockdep_assert_held(&mddev->reconfig_mutex);
> - if (--mddev->suspended)
> +
> + /* can't concurrent with __mddev_suspend() and __mddev_resume() */
> + mutex_lock(&mddev->suspend_mutex);
> + if (--mddev->suspended) {
> + mutex_unlock(&mddev->suspend_mutex);
> return;
> + }
>
> /* entred the memalloc scope from mddev_suspend() */
> memalloc_noio_restore(mddev->noio_flag);
> @@ -477,9 +494,72 @@ void mddev_resume(struct mddev *mddev)
> 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);
> }
> EXPORT_SYMBOL_GPL(mddev_resume);
>
> +void __mddev_suspend(struct mddev *mddev)
> +{
> +
> + /*
> + * hold reconfig_mutex to wait for normal io will deadlock, because
> + * other context can't update super_block, and normal io can rely on
> + * updating super_block.
> + */
> + lockdep_assert_not_held(&mddev->reconfig_mutex);
> +
> + mutex_lock(&mddev->suspend_mutex);
> +
> + if (mddev->suspended) {
> + WRITE_ONCE(mddev->suspended, mddev->suspended + 1);
> + mutex_unlock(&mddev->suspend_mutex);
> + return;
> + }
> +
> + percpu_ref_kill(&mddev->active_io);
> + wait_event(mddev->sb_wait, percpu_ref_is_zero(&mddev->active_io));
> +
> + /*
> + * For raid456, io might be waiting for reshape to make progress,
> + * allow new reshape to start while waiting for io to be done to
> + * prevent deadlock.
> + */
> + WRITE_ONCE(mddev->suspended, mddev->suspended + 1);
It changes the order of setting suspended and checking active_io.
suspended is used to stop I/O. Now it checks active_io first and then
adds suspended, if the i/o doesn't stop, it looks like active_io can't
be 0. So it will stuck at waiting active_io to be 0?
Best Regards
Xiao
> +
> + del_timer_sync(&mddev->safemode_timer);
> + /* restrict memory reclaim I/O during raid array is suspend */
> + mddev->noio_flag = memalloc_noio_save();
> +
> + mutex_unlock(&mddev->suspend_mutex);
> +}
> +EXPORT_SYMBOL_GPL(__mddev_suspend);
> +
> +void __mddev_resume(struct mddev *mddev)
> +{
> + lockdep_assert_not_held(&mddev->reconfig_mutex);
> +
> + mutex_lock(&mddev->suspend_mutex);
> + WRITE_ONCE(mddev->suspended, mddev->suspended - 1);
> + if (mddev->suspended) {
> + mutex_unlock(&mddev->suspend_mutex);
> + return;
> + }
> +
> + /* entred the memalloc scope from __mddev_suspend() */
> + memalloc_noio_restore(mddev->noio_flag);
> +
> + percpu_ref_resurrect(&mddev->active_io);
> + wake_up(&mddev->sb_wait);
> +
> + 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);
> +}
> +EXPORT_SYMBOL_GPL(__mddev_resume);
> +
> /*
> * Generic flush handling for md
> */
> @@ -667,6 +747,7 @@ int mddev_init(struct mddev *mddev)
> mutex_init(&mddev->open_mutex);
> mutex_init(&mddev->reconfig_mutex);
> mutex_init(&mddev->sync_mutex);
> + mutex_init(&mddev->suspend_mutex);
> mutex_init(&mddev->bitmap_info.mutex);
> INIT_LIST_HEAD(&mddev->disks);
> INIT_LIST_HEAD(&mddev->all_mddevs);
> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index fb3b123f16dd..1103e6b08ad9 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -316,6 +316,7 @@ struct mddev {
> unsigned long sb_flags;
>
> int suspended;
> + struct mutex suspend_mutex;
> struct percpu_ref active_io;
> int ro;
> int sysfs_active; /* set when sysfs deletes
> @@ -811,6 +812,8 @@ extern void md_rdev_clear(struct md_rdev *rdev);
> extern void md_handle_request(struct mddev *mddev, struct bio *bio);
> extern void mddev_suspend(struct mddev *mddev);
> extern void mddev_resume(struct mddev *mddev);
> +extern void __mddev_suspend(struct mddev *mddev);
> +extern void __mddev_resume(struct mddev *mddev);
>
> extern void md_reload_sb(struct mddev *mddev, int raid_disk);
> extern void md_update_sb(struct mddev *mddev, int force);
> --
> 2.39.2
>
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