Illumos #883: ZIL reuse during remount corruption

Moving the zil_free() cleanup to zil_close() prevents this
problem from occurring in the first place.  There is a very
good description of the issue and fix in Illumus #883.

Reviewed by: Matt Ahrens <[email protected]>
Reviewed by: Adam Leventhal <[email protected]>
Reviewed by: Albert Lee <[email protected]>
Reviewed by: Gordon Ross <[email protected]>
Reviewed by: Garrett D'Amore <[email protected]>
Reivewed by: Dan McDonald <[email protected]>
Approved by: Gordon Ross <[email protected]>

References to Illumos issue and patch:
- https://www.illumos.org/issues/883
- https://github.com/illumos/illumos-gate/commit/c9ba2a43cb

Signed-off-by: Brian Behlendorf <[email protected]>
Issue #340

1 files changed, 24 insertions, 16 deletions

diff --git a/module/zfs/zil.c b/module/zfs/zil.c
index 8aa811db2..5296b38be 100644
--- a/module/zfs/zil.c
+++ b/module/zfs/zil.c
@@ -20,6 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011 by Delphix. All rights reserved.
  */
 
 /* Portions Copyright 2010 Robert Milkowski */
@@ -562,7 +563,7 @@ zil_destroy(zilog_t *zilog, boolean_t keep_first)
 
 	if (!list_is_empty(&zilog->zl_lwb_list)) {
 		ASSERT(zh->zh_claim_txg == 0);
-		ASSERT(!keep_first);
+		VERIFY(!keep_first);
 		while ((lwb = list_head(&zilog->zl_lwb_list)) != NULL) {
 			list_remove(&zilog->zl_lwb_list, lwb);
 			if (lwb->lwb_buf != NULL)
@@ -1665,21 +1666,11 @@ zil_alloc(objset_t *os, zil_header_t *zh_phys)
 void
 zil_free(zilog_t *zilog)
 {
-	lwb_t *head_lwb;
 	int i;
 
 	zilog->zl_stop_sync = 1;
 
-	/*
-	 * After zil_close() there should only be one lwb with a buffer.
-	 */
-	head_lwb = list_head(&zilog->zl_lwb_list);
-	if (head_lwb) {
-		ASSERT(head_lwb == list_tail(&zilog->zl_lwb_list));
-		list_remove(&zilog->zl_lwb_list, head_lwb);
-		zio_buf_free(head_lwb->lwb_buf, head_lwb->lwb_sz);
-		kmem_cache_free(zil_lwb_cache, head_lwb);
-	}
+	ASSERT(list_is_empty(&zilog->zl_lwb_list));
 	list_destroy(&zilog->zl_lwb_list);
 
 	avl_destroy(&zilog->zl_vdev_tree);
@@ -1719,6 +1710,10 @@ zil_open(objset_t *os, zil_get_data_t *get_data)
 {
 	zilog_t *zilog = dmu_objset_zil(os);
 
+	ASSERT(zilog->zl_clean_taskq == NULL);
+	ASSERT(zilog->zl_get_data == NULL);
+	ASSERT(list_is_empty(&zilog->zl_lwb_list));
+
 	zilog->zl_get_data = get_data;
 	zilog->zl_clean_taskq = taskq_create("zil_clean", 1, minclsyspri,
 	    2, 2, TASKQ_PREPOPULATE);
@@ -1732,7 +1727,7 @@ zil_open(objset_t *os, zil_get_data_t *get_data)
 void
 zil_close(zilog_t *zilog)
 {
-	lwb_t *tail_lwb;
+	lwb_t *lwb;
 	uint64_t txg = 0;
 
 	zil_commit(zilog, 0); /* commit all itx */
@@ -1744,9 +1739,9 @@ zil_close(zilog_t *zilog)
 	 * destroy the zl_clean_taskq.
 	 */
 	mutex_enter(&zilog->zl_lock);
-	tail_lwb = list_tail(&zilog->zl_lwb_list);
-	if (tail_lwb != NULL)
-		txg = tail_lwb->lwb_max_txg;
+	lwb = list_tail(&zilog->zl_lwb_list);
+	if (lwb != NULL)
+		txg = lwb->lwb_max_txg;
 	mutex_exit(&zilog->zl_lock);
 	if (txg)
 		txg_wait_synced(zilog->zl_dmu_pool, txg);
@@ -1754,6 +1749,19 @@ zil_close(zilog_t *zilog)
 	taskq_destroy(zilog->zl_clean_taskq);
 	zilog->zl_clean_taskq = NULL;
 	zilog->zl_get_data = NULL;
+
+	/*
+	 * We should have only one LWB left on the list; remove it now.
+	 */
+	mutex_enter(&zilog->zl_lock);
+	lwb = list_head(&zilog->zl_lwb_list);
+	if (lwb != NULL) {
+		ASSERT(lwb == list_tail(&zilog->zl_lwb_list));
+		list_remove(&zilog->zl_lwb_list, lwb);
+		zio_buf_free(lwb->lwb_buf, lwb->lwb_sz);
+		kmem_cache_free(zil_lwb_cache, lwb);
+	}
+	mutex_exit(&zilog->zl_lock);
 }
 
 /*