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zfs: allow a zvol to be used as a pool vdev, again

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Do this by checking if spa_namespace_lock is already held and not taking
it again in that case.
Add a comment explaining why that is done and why it is safe.

Reviewed by:	pjd
MFC after:	24 days
This commit is contained in:
Andriy Gapon 2012-09-22 17:42:53 +00:00
parent a6512306ce
commit 81c4584e30
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=240831
1 changed files with 33 additions and 15 deletions
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48
sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zvol.c
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@ -878,27 +878,36 @@ zvol_open(struct g_provider *pp, int flag, int count)
{
zvol_state_t *zv;
int err = 0;
boolean_t locked = B_FALSE;
if (MUTEX_HELD(&spa_namespace_lock)) {
/*
* If the spa_namespace_lock is being held, it means that ZFS
* is trying to open ZVOL as its VDEV. This is not supported.
*/
return (EOPNOTSUPP);
/*
* Protect against recursively entering spa_namespace_lock
* when spa_open() is used for a pool on a (local) ZVOL(s).
* This is needed since we replaced upstream zfsdev_state_lock
* with spa_namespace_lock in the ZVOL code.
* We are using the same trick as spa_open().
* Note that calls in zvol_first_open which need to resolve
* pool name to a spa object will enter spa_open()
* recursively, but that function already has all the
* necessary protection.
*/
if (!MUTEX_HELD(&spa_namespace_lock)) {
mutex_enter(&spa_namespace_lock);
locked = B_TRUE;
}
mutex_enter(&spa_namespace_lock);
zv = pp->private;
if (zv == NULL) {
mutex_exit(&spa_namespace_lock);
if (locked)
mutex_exit(&spa_namespace_lock);
return (ENXIO);
}
if (zv->zv_total_opens == 0)
err = zvol_first_open(zv);
if (err) {
mutex_exit(&spa_namespace_lock);
if (locked)
mutex_exit(&spa_namespace_lock);
return (err);
}
if ((flag & FWRITE) && (zv->zv_flags & ZVOL_RDONLY)) {
@ -920,13 +929,15 @@ zvol_open(struct g_provider *pp, int flag, int count)
#endif
zv->zv_total_opens += count;
mutex_exit(&spa_namespace_lock);
if (locked)
mutex_exit(&spa_namespace_lock);
return (err);
out:
if (zv->zv_total_opens == 0)
zvol_last_close(zv);
mutex_exit(&spa_namespace_lock);
if (locked)
mutex_exit(&spa_namespace_lock);
return (err);
}
@ -936,12 +947,18 @@ zvol_close(struct g_provider *pp, int flag, int count)
{
zvol_state_t *zv;
int error = 0;
boolean_t locked = B_FALSE;
mutex_enter(&spa_namespace_lock);
/* See comment in zvol_open(). */
if (!MUTEX_HELD(&spa_namespace_lock)) {
mutex_enter(&spa_namespace_lock);
locked = B_TRUE;
}
zv = pp->private;
if (zv == NULL) {
mutex_exit(&spa_namespace_lock);
if (locked)
mutex_exit(&spa_namespace_lock);
return (ENXIO);
}
@ -964,7 +981,8 @@ zvol_close(struct g_provider *pp, int flag, int count)
if (zv->zv_total_opens == 0)
zvol_last_close(zv);
mutex_exit(&spa_namespace_lock);
if (locked)
mutex_exit(&spa_namespace_lock);
return (error);
}