From b5470dc5fc18a8ff6517c3bb538d1479e58ecb02 Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Fri, 27 Jun 2008 21:44:04 -0700 Subject: md: resolve external metadata handling deadlock in md_allow_write md_allow_write() marks the metadata dirty while holding mddev->lock and then waits for the write to complete. For externally managed metadata this causes a deadlock as userspace needs to take the lock to communicate that the metadata update has completed. Change md_allow_write() in the 'external' case to start the 'mark active' operation and then return -EAGAIN. The expected side effects while waiting for userspace to write 'active' to 'array_state' are holding off reshape (code currently handles -ENOMEM), cause some 'stripe_cache_size' change requests to fail, cause some GET_BITMAP_FILE ioctl requests to fall back to GFP_NOIO, and cause updates to 'raid_disks' to fail. Except for 'stripe_cache_size' changes these failures can be mitigated by coordinating with mdmon. md_write_start() still prevents writes from occurring until the metadata handler has had a chance to take action as it unconditionally waits for MD_CHANGE_CLEAN to be cleared. [neilb@suse.de: return -EAGAIN, try GFP_NOIO] Signed-off-by: Dan Williams --- drivers/md/md.c | 27 ++++++++++++++++----------- 1 file changed, 16 insertions(+), 11 deletions(-) (limited to 'drivers/md/md.c') diff --git a/drivers/md/md.c b/drivers/md/md.c index df1230af02c..43d033d9a05 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -4172,9 +4172,11 @@ static int get_bitmap_file(mddev_t * mddev, void __user * arg) char *ptr, *buf = NULL; int err = -ENOMEM; - md_allow_write(mddev); + if (md_allow_write(mddev)) + file = kmalloc(sizeof(*file), GFP_NOIO); + else + file = kmalloc(sizeof(*file), GFP_KERNEL); - file = kmalloc(sizeof(*file), GFP_KERNEL); if (!file) goto out; @@ -5667,15 +5669,18 @@ void md_write_end(mddev_t *mddev) * may proceed without blocking. It is important to call this before * attempting a GFP_KERNEL allocation while holding the mddev lock. * Must be called with mddev_lock held. + * + * In the ->external case MD_CHANGE_CLEAN can not be cleared until mddev->lock + * is dropped, so return -EAGAIN after notifying userspace. */ -void md_allow_write(mddev_t *mddev) +int md_allow_write(mddev_t *mddev) { if (!mddev->pers) - return; + return 0; if (mddev->ro) - return; + return 0; if (!mddev->pers->sync_request) - return; + return 0; spin_lock_irq(&mddev->write_lock); if (mddev->in_sync) { @@ -5686,14 +5691,14 @@ void md_allow_write(mddev_t *mddev) mddev->safemode = 1; spin_unlock_irq(&mddev->write_lock); md_update_sb(mddev, 0); - sysfs_notify(&mddev->kobj, NULL, "array_state"); - /* wait for the dirty state to be recorded in the metadata */ - wait_event(mddev->sb_wait, - !test_bit(MD_CHANGE_CLEAN, &mddev->flags) && - !test_bit(MD_CHANGE_PENDING, &mddev->flags)); } else spin_unlock_irq(&mddev->write_lock); + + if (test_bit(MD_CHANGE_CLEAN, &mddev->flags)) + return -EAGAIN; + else + return 0; } EXPORT_SYMBOL_GPL(md_allow_write); -- cgit v1.2.3