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Date: Fri, 29 Oct 2010 15:13:37 +1100
From: Neil Brown <neilb@...e.de>
To: Tejun Heo <tj@...nel.org>
Cc: lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2.6.36-rc7] md: fix and update workqueue usage
On Fri, 15 Oct 2010 15:36:08 +0200
Tejun Heo <tj@...nel.org> wrote:
> Workqueue usage in md has two problems.
>
> * Flush can be used during or depended upon by memory reclaim, but md
> uses the system workqueue for flush_work which may lead to deadlock.
>
> * md depends on flush_scheduled_work() to achieve exclusion against
> completion of removal of previous instances. flush_scheduled_work()
> may incur unexpected amount of delay and is scheduled to be removed.
>
> This patch adds two workqueues to md - md_wq and md_misc_wq. The
> former is guaranteed to make forward progress under memory pressure
> and serves flush_work. The latter serves as the flush domain for
> other works.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> ---
> Neil, this patch doesn't conflict with the pending barrier changes in
> block tree and should be safe to apply to md tree.
Hi Tejun,
Sorry for not replying to this earlier.
It seems to make sense, and passes all my testing so I'm happy with it.
I'll go to Linus shortly.
Thanks,
NeilBrown
>
> Thanks.
>
> drivers/md/md.c | 64 +++++++++++++++++++++++++++++++++++++-------------------
> 1 file changed, 43 insertions(+), 21 deletions(-)
>
> Index: work/drivers/md/md.c
> ===================================================================
> --- work.orig/drivers/md/md.c
> +++ work/drivers/md/md.c
> @@ -68,6 +68,8 @@ static DEFINE_SPINLOCK(pers_lock);
> static void md_print_devices(void);
>
> static DECLARE_WAIT_QUEUE_HEAD(resync_wait);
> +static struct workqueue_struct *md_wq;
> +static struct workqueue_struct *md_misc_wq;
>
> #define MD_BUG(x...) { printk("md: bug in file %s, line %d\n", __FILE__, __LINE__); md_print_devices(); }
>
> @@ -299,7 +301,7 @@ static void md_end_flush(struct bio *bio
>
> if (atomic_dec_and_test(&mddev->flush_pending)) {
> /* The pre-request flush has finished */
> - schedule_work(&mddev->flush_work);
> + queue_work(md_wq, &mddev->flush_work);
> }
> bio_put(bio);
> }
> @@ -368,7 +370,7 @@ void md_flush_request(mddev_t *mddev, st
> submit_flushes(mddev);
>
> if (atomic_dec_and_test(&mddev->flush_pending))
> - schedule_work(&mddev->flush_work);
> + queue_work(md_wq, &mddev->flush_work);
> }
> EXPORT_SYMBOL(md_flush_request);
>
> @@ -435,14 +437,13 @@ static void mddev_put(mddev_t *mddev)
> * so destroy it */
> list_del(&mddev->all_mddevs);
> if (mddev->gendisk) {
> - /* we did a probe so need to clean up.
> - * Call schedule_work inside the spinlock
> - * so that flush_scheduled_work() after
> - * mddev_find will succeed in waiting for the
> - * work to be done.
> + /* We did a probe so need to clean up. Call
> + * queue_work inside the spinlock so that
> + * flush_workqueue() after mddev_find will
> + * succeed in waiting for the work to be done.
> */
> INIT_WORK(&mddev->del_work, mddev_delayed_delete);
> - schedule_work(&mddev->del_work);
> + queue_work(md_misc_wq, &mddev->del_work);
> } else
> kfree(mddev);
> }
> @@ -1849,7 +1850,7 @@ static void unbind_rdev_from_array(mdk_r
> synchronize_rcu();
> INIT_WORK(&rdev->del_work, md_delayed_delete);
> kobject_get(&rdev->kobj);
> - schedule_work(&rdev->del_work);
> + queue_work(md_misc_wq, &rdev->del_work);
> }
>
> /*
> @@ -4191,10 +4192,10 @@ static int md_alloc(dev_t dev, char *nam
> shift = partitioned ? MdpMinorShift : 0;
> unit = MINOR(mddev->unit) >> shift;
>
> - /* wait for any previous instance if this device
> - * to be completed removed (mddev_delayed_delete).
> + /* wait for any previous instance if this device to be
> + * completely removed (mddev_delayed_delete).
> */
> - flush_scheduled_work();
> + flush_workqueue(md_misc_wq);
>
> mutex_lock(&disks_mutex);
> error = -EEXIST;
> @@ -5891,7 +5892,7 @@ static int md_open(struct block_device *
> */
> mddev_put(mddev);
> /* Wait until bdev->bd_disk is definitely gone */
> - flush_scheduled_work();
> + flush_workqueue(md_misc_wq);
> /* Then retry the open from the top */
> unlock_kernel();
> return -ERESTARTSYS;
> @@ -6051,7 +6052,7 @@ void md_error(mddev_t *mddev, mdk_rdev_t
> set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
> md_wakeup_thread(mddev->thread);
> if (mddev->event_work.func)
> - schedule_work(&mddev->event_work);
> + queue_work(md_misc_wq, &mddev->event_work);
> md_new_event_inintr(mddev);
> }
>
> @@ -7211,12 +7212,23 @@ static void md_geninit(void)
>
> static int __init md_init(void)
> {
> - if (register_blkdev(MD_MAJOR, "md"))
> - return -1;
> - if ((mdp_major=register_blkdev(0, "mdp"))<=0) {
> - unregister_blkdev(MD_MAJOR, "md");
> - return -1;
> - }
> + int ret = -ENOMEM;
> +
> + md_wq = alloc_workqueue("md", WQ_RESCUER, 0);
> + if (!md_wq)
> + goto err_wq;
> +
> + md_misc_wq = alloc_workqueue("md_misc", 0, 0);
> + if (!md_misc_wq)
> + goto err_misc_wq;
> +
> + if ((ret = register_blkdev(MD_MAJOR, "md")) < 0)
> + goto err_md;
> +
> + if ((ret = register_blkdev(0, "mdp")) < 0)
> + goto err_mdp;
> + mdp_major = ret;
> +
> blk_register_region(MKDEV(MD_MAJOR, 0), 1UL<<MINORBITS, THIS_MODULE,
> md_probe, NULL, NULL);
> blk_register_region(MKDEV(mdp_major, 0), 1UL<<MINORBITS, THIS_MODULE,
> @@ -7227,8 +7239,16 @@ static int __init md_init(void)
>
> md_geninit();
> return 0;
> -}
>
> +err_mdp:
> + unregister_blkdev(MD_MAJOR, "md");
> +err_md:
> + destroy_workqueue(md_misc_wq);
> +err_misc_wq:
> + destroy_workqueue(md_wq);
> +err_wq:
> + return ret;
> +}
>
> #ifndef MODULE
>
> @@ -7315,6 +7335,8 @@ static __exit void md_exit(void)
> export_array(mddev);
> mddev->hold_active = 0;
> }
> + destroy_workqueue(md_misc_wq);
> + destroy_workqueue(md_wq);
> }
>
> subsys_initcall(md_init);
--
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