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md: resolve external metadata handling deadlock in md_allow_write

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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 <dan.j.williams@intel.com>
This commit is contained in:
Dan Williams
2008-06-27 21:44:04 -07:00
parent 1fe797e67f
commit b5470dc5fc
4 changed files with 30 additions and 17 deletions
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27
drivers/md/md.c
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@@ -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);