zvol: ensure device minors are properly cleaned up

Currently, if a minor is in use when we try to remove it, we'll skip it and never come back to it again. Since the zvol state is hung off the minor in the kernel, this can get us into weird situations if something tries to use it after the removal fails. It's even worse at pool export, as there's now a vestigial zvol state with no pool under it. It's weirder again if the pool is subsequently reimported, as the zvol code (reasonably) assumes the zvol state has been properly setup, when it's actually left over from the previous import of the pool. This commit attempts to tackle that by setting a flag on the zvol if its minor can't be removed, and then checking that flag when a request is made and rejecting it, thus stopping new work coming in. The flag also causes a condvar to be signaled when the last client finishes. For the case where a single minor is being removed (eg changing volmode), it will wait for this signal before proceeding. Meanwhile, when removing all minors, a background task is created for each minor that couldn't be removed on the spot, and those tasks then wake and clean up. Since any new tasks are queued on to the pool's spa_zvol_taskq, spa_export_common() will continue to wait at export until all minors are removed. Reviewed-by: Tony Hutter <hutter2@llnl.gov> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Sponsored-by: Klara, Inc. Sponsored-by: Wasabi Technology, Inc. Signed-off-by: Rob Norris <rob.norris@klarasystems.com> Closes #14872 Closes #16364
2026-05-22 02:27:36 +03:00 · 2024-07-18 13:24:05 +10:00
parent f3a9746f21
commit cf80a803d5
4 changed files with 122 additions and 26 deletions
@@ -30,6 +30,7 @@
 * Copyright (c) 2012, 2017 by Delphix. All rights reserved.
 * Copyright (c) 2013, Joyent, Inc. All rights reserved.
 * Copyright (c) 2014 Integros [integros.com]
+ * Copyright (c) 2024, Klara, Inc.
 */

 /* Portions Copyright 2011 Martin Matuska <mm@FreeBSD.org> */
@@ -251,7 +252,7 @@ retry:
 	}

 	mutex_enter(&zv->zv_state_lock);
-	if (zv->zv_zso->zso_dying) {
+	if (zv->zv_zso->zso_dying || zv->zv_flags & ZVOL_REMOVING) {
 		rw_exit(&zvol_state_lock);
 		err = SET_ERROR(ENXIO);
 		goto out_zv_locked;
@@ -683,6 +684,11 @@ zvol_geom_bio_strategy(struct bio *bp)

 	rw_enter(&zv->zv_suspend_lock, ZVOL_RW_READER);

+	if (zv->zv_flags & ZVOL_REMOVING) {
+		error = SET_ERROR(ENXIO);
+		goto resume;
+	}
+
 	switch (bp->bio_cmd) {
 	case BIO_READ:
 		doread = B_TRUE;
@@ -1374,6 +1380,7 @@ zvol_os_free(zvol_state_t *zv)
 	}

 	mutex_destroy(&zv->zv_state_lock);
+	cv_destroy(&zv->zv_removing_cv);
 	dataset_kstats_destroy(&zv->zv_kstat);
 	kmem_free(zv->zv_zso, sizeof (struct zvol_state_os));
 	kmem_free(zv, sizeof (zvol_state_t));
@@ -1431,6 +1438,7 @@ zvol_os_create_minor(const char *name)
 	zv = kmem_zalloc(sizeof (*zv), KM_SLEEP);
 	zv->zv_hash = hash;
 	mutex_init(&zv->zv_state_lock, NULL, MUTEX_DEFAULT, NULL);
+	cv_init(&zv->zv_removing_cv, NULL, CV_DEFAULT, NULL);
 	zv->zv_zso = kmem_zalloc(sizeof (struct zvol_state_os), KM_SLEEP);
 	zv->zv_volmode = volmode;
 	if (zv->zv_volmode == ZFS_VOLMODE_GEOM) {
@@ -21,6 +21,7 @@
 /*
 * Copyright (c) 2012, 2020 by Delphix. All rights reserved.
 * Copyright (c) 2024, Rob Norris <robn@despairlabs.com>
+ * Copyright (c) 2024, Klara, Inc.
 */

 #include <sys/dataset_kstats.h>
@@ -527,6 +528,11 @@ zvol_request_impl(zvol_state_t *zv, struct bio *bio, struct request *rq,
 	uint64_t size = io_size(bio, rq);
 	int rw = io_data_dir(bio, rq);

+	if (unlikely(zv->zv_flags & ZVOL_REMOVING)) {
+		END_IO(zv, bio, rq, -SET_ERROR(ENXIO));
+		goto out;
+	}
+
 	if (zvol_request_sync)
 		force_sync = 1;

@@ -735,6 +741,13 @@ retry:
 	}

 	mutex_enter(&zv->zv_state_lock);
+
+	if (unlikely(zv->zv_flags & ZVOL_REMOVING)) {
+		mutex_exit(&zv->zv_state_lock);
+		rw_exit(&zvol_state_lock);
+		return (-SET_ERROR(ENXIO));
+	}
+
 	/*
 	 * Make sure zvol is not suspended during first open
 	 * (hold zv_suspend_lock) and respect proper lock acquisition
@@ -1368,6 +1381,7 @@ zvol_alloc(dev_t dev, const char *name, uint64_t volblocksize)

 	list_link_init(&zv->zv_next);
 	mutex_init(&zv->zv_state_lock, NULL, MUTEX_DEFAULT, NULL);
+	cv_init(&zv->zv_removing_cv, NULL, CV_DEFAULT, NULL);

 #ifdef HAVE_BLK_MQ
 	zv->zv_zso->use_blk_mq = zvol_use_blk_mq;
@@ -1488,6 +1502,7 @@ zvol_os_free(zvol_state_t *zv)
 	ida_simple_remove(&zvol_ida,
 	    MINOR(zv->zv_zso->zvo_dev) >> ZVOL_MINOR_BITS);

+	cv_destroy(&zv->zv_removing_cv);
 	mutex_destroy(&zv->zv_state_lock);
 	dataset_kstats_destroy(&zv->zv_kstat);

@@ -37,6 +37,7 @@
 * Copyright 2014 Nexenta Systems, Inc.  All rights reserved.
 * Copyright (c) 2016 Actifio, Inc. All rights reserved.
 * Copyright (c) 2012, 2019 by Delphix. All rights reserved.
+ * Copyright (c) 2024, Klara, Inc.
 */

 /*
@@ -868,6 +869,9 @@ zvol_resume(zvol_state_t *zv)
 	 */
 	atomic_dec(&zv->zv_suspend_ref);

+	if (zv->zv_flags & ZVOL_REMOVING)
+		cv_broadcast(&zv->zv_removing_cv);
+
 	return (SET_ERROR(error));
 }

@@ -903,6 +907,9 @@ zvol_last_close(zvol_state_t *zv)
 	ASSERT(RW_READ_HELD(&zv->zv_suspend_lock));
 	ASSERT(MUTEX_HELD(&zv->zv_state_lock));

+	if (zv->zv_flags & ZVOL_REMOVING)
+		cv_broadcast(&zv->zv_removing_cv);
+
 	zvol_shutdown_zv(zv);

 	dmu_objset_disown(zv->zv_objset, 1, zv);
@@ -1195,6 +1202,41 @@ zvol_create_minor(const char *name)
 * Remove minors for specified dataset including children and snapshots.
 */

+/*
+ * Remove the minor for a given zvol. This will do it all:
+ *  - flag the zvol for removal, so new requests are rejected
+ *  - wait until outstanding requests are completed
+ *  - remove it from lists
+ *  - free it
+ * It's also usable as a taskq task, and smells nice too.
+ */
+static void
+zvol_remove_minor_task(void *arg)
+{
+	zvol_state_t *zv = (zvol_state_t *)arg;
+
+	ASSERT(!RW_LOCK_HELD(&zvol_state_lock));
+	ASSERT(!MUTEX_HELD(&zv->zv_state_lock));
+
+	mutex_enter(&zv->zv_state_lock);
+	while (zv->zv_open_count > 0 || atomic_read(&zv->zv_suspend_ref)) {
+		zv->zv_flags |= ZVOL_REMOVING;
+		cv_wait(&zv->zv_removing_cv, &zv->zv_state_lock);
+	}
+	mutex_exit(&zv->zv_state_lock);
+
+	rw_enter(&zvol_state_lock, RW_WRITER);
+	mutex_enter(&zv->zv_state_lock);
+
+	zvol_remove(zv);
+	zvol_os_clear_private(zv);
+
+	mutex_exit(&zv->zv_state_lock);
+	rw_exit(&zvol_state_lock);
+
+	zvol_os_free(zv);
+}
+
 static void
 zvol_free_task(void *arg)
 {
@@ -1207,11 +1249,13 @@ zvol_remove_minors_impl(const char *name)
 	zvol_state_t *zv, *zv_next;
 	int namelen = ((name) ? strlen(name) : 0);
 	taskqid_t t;
-	list_t free_list;
+	list_t delay_list, free_list;

 	if (zvol_inhibit_dev)
 		return;

+	list_create(&delay_list, sizeof (zvol_state_t),
+	    offsetof(zvol_state_t, zv_next));
 	list_create(&free_list, sizeof (zvol_state_t),
 	    offsetof(zvol_state_t, zv_next));

@@ -1230,9 +1274,24 @@ zvol_remove_minors_impl(const char *name)
 			 * one is currently using this zv
 			 */

-			/* If in use, leave alone */
+			/*
+			 * If in use, try to throw everyone off and try again
+			 * later.
+			 */
 			if (zv->zv_open_count > 0 ||
 			    atomic_read(&zv->zv_suspend_ref)) {
+				zv->zv_flags |= ZVOL_REMOVING;
+				t = taskq_dispatch(
+				    zv->zv_objset->os_spa->spa_zvol_taskq,
+				    zvol_remove_minor_task, zv, TQ_SLEEP);
+				if (t == TASKQID_INVALID) {
+					/*
+					 * Couldn't create the task, so we'll
+					 * do it in place once the loop is
+					 * finished.
+					 */
+					list_insert_head(&delay_list, zv);
+				}
 				mutex_exit(&zv->zv_state_lock);
 				continue;
 			}
@@ -1259,7 +1318,11 @@ zvol_remove_minors_impl(const char *name)
 	}
 	rw_exit(&zvol_state_lock);

-	/* Drop zvol_state_lock before calling zvol_free() */
+	/* Wait for zvols that we couldn't create a remove task for */
+	while ((zv = list_remove_head(&delay_list)) != NULL)
+		zvol_remove_minor_task(zv);
+
+	/* Free any that we couldn't free in parallel earlier */
 	while ((zv = list_remove_head(&free_list)) != NULL)
 		zvol_os_free(zv);
 }
@@ -1279,33 +1342,38 @@ zvol_remove_minor_impl(const char *name)
 		zv_next = list_next(&zvol_state_list, zv);

 		mutex_enter(&zv->zv_state_lock);
-		if (strcmp(zv->zv_name, name) == 0) {
-			/*
-			 * By holding zv_state_lock here, we guarantee that no
-			 * one is currently using this zv
-			 */
-
-			/* If in use, leave alone */
-			if (zv->zv_open_count > 0 ||
-			    atomic_read(&zv->zv_suspend_ref)) {
-				mutex_exit(&zv->zv_state_lock);
-				continue;
-			}
-			zvol_remove(zv);
-
-			zvol_os_clear_private(zv);
-			mutex_exit(&zv->zv_state_lock);
+		if (strcmp(zv->zv_name, name) == 0)
+			/* Found, leave the the loop with zv_lock held */
 			break;
-		} else {
-			mutex_exit(&zv->zv_state_lock);
-		}
+		mutex_exit(&zv->zv_state_lock);
 	}

-	/* Drop zvol_state_lock before calling zvol_free() */
+	if (zv == NULL) {
+		rw_exit(&zvol_state_lock);
+		return;
+	}
+
+	ASSERT(MUTEX_HELD(&zv->zv_state_lock));
+
+	if (zv->zv_open_count > 0 || atomic_read(&zv->zv_suspend_ref)) {
+		/*
+		 * In use, so try to throw everyone off, then wait
+		 * until finished.
+		 */
+		zv->zv_flags |= ZVOL_REMOVING;
+		mutex_exit(&zv->zv_state_lock);
+		rw_exit(&zvol_state_lock);
+		zvol_remove_minor_task(zv);
+		return;
+	}
+
+	zvol_remove(zv);
+	zvol_os_clear_private(zv);
+
+	mutex_exit(&zv->zv_state_lock);
 	rw_exit(&zvol_state_lock);

-	if (zv != NULL)
-		zvol_os_free(zv);
+	zvol_os_free(zv);
 }

 /*