Author: mav
Date: Mon Aug 10 19:38:07 2015
New Revision: 286589
URL: https://svnweb.freebsd.org/changeset/base/286589
Log:
MFV 286588: 5820 verify failed in zio_done(): BP_EQUAL(bp, io_bp_orig)
Reviewed by: Alex Reece <a...@delphix.com>
Reviewed by: George Wilson <geo...@delphix.com>
Reviewed by: Steven Hartland <kill...@multiplay.co.uk>
Approved by: Garrett D'Amore <garr...@damore.org>
Author: Matthew Ahrens <mahr...@delphix.com>
illumod/illumos-gate@34e8acef009195effafdcf6417aec385e241796e
Modified:
head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c
Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c Mon Aug 10
19:37:43 2015 (r286588)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c Mon Aug 10
19:38:07 2015 (r286589)
@@ -1652,19 +1652,32 @@ dmu_sync(zio_t *pio, uint64_t txg, dmu_s
ASSERT(dr->dr_next == NULL || dr->dr_next->dr_txg < txg);
/*
- * Assume the on-disk data is X, the current syncing data is Y,
- * and the current in-memory data is Z (currently in dmu_sync).
- * X and Z are identical but Y is has been modified. Normally,
- * when X and Z are the same we will perform a nopwrite but if Y
- * is different we must disable nopwrite since the resulting write
- * of Y to disk can free the block containing X. If we allowed a
- * nopwrite to occur the block pointing to Z would reference a freed
- * block. Since this is a rare case we simplify this by disabling
- * nopwrite if the current dmu_sync-ing dbuf has been modified in
- * a previous transaction.
+ * Assume the on-disk data is X, the current syncing data (in
+ * txg - 1) is Y, and the current in-memory data is Z (currently
+ * in dmu_sync).
+ *
+ * We usually want to perform a nopwrite if X and Z are the
+ * same. However, if Y is different (i.e. the BP is going to
+ * change before this write takes effect), then a nopwrite will
+ * be incorrect - we would override with X, which could have
+ * been freed when Y was written.
+ *
+ * (Note that this is not a concern when we are nop-writing from
+ * syncing context, because X and Y must be identical, because
+ * all previous txgs have been synced.)
+ *
+ * Therefore, we disable nopwrite if the current BP could change
+ * before this TXG. There are two ways it could change: by
+ * being dirty (dr_next is non-NULL), or by being freed
+ * (dnode_block_freed()). This behavior is verified by
+ * zio_done(), which VERIFYs that the override BP is identical
+ * to the on-disk BP.
*/
- if (dr->dr_next)
+ DB_DNODE_ENTER(db);
+ dn = DB_DNODE(db);
+ if (dr->dr_next != NULL || dnode_block_freed(dn, db->db_blkid))
zp.zp_nopwrite = B_FALSE;
+ DB_DNODE_EXIT(db);
ASSERT(dr->dr_txg == txg);
if (dr->dt.dl.dr_override_state == DR_IN_DMU_SYNC ||
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