svn commit: r305325 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs

[Alexander Motin]

Author: mav
Date: Sat Sep  3 08:43:43 2016
New Revision: 305325
URL: https://svnweb.freebsd.org/changeset/base/305325

Log:
  MFV r303078:
  7086 ztest attempts dva_get_dsize_sync on an embedded blockpointer
  
  illumos/illumos-gate at 926549256b71acd595f69b236779ff6b78fa08ef
  https://github.com/illumos/illumos-gate/commit/926549256b71acd595f69b236779ff6b7
  8fa08ef
  
  https://www.illumos.org/issues/7086
    In dbuf_dirty(), we need to grab the dn_struct_rwlock before looking at the
    db_blkptr, to prevent it from being changed by syncing context.
    Otherwise we may see that ztest got a segfault from this stack:
    libzpool.so.1`dva_get_dsize_sync+0x98(872f000, b32b240, fed7811b, 0, b4cda20,
  0)
    libzpool.so.1`bp_get_dsize+0x60(872f000, b32b240, 0, 97cb780, 9d4c1a8, 0)
    libzpool.so.1`dbuf_dirty+0x9b3(ce0a100, 97cb780, 9, fecd2530)
    libzpool.so.1`dmu_buf_will_dirty+0xc3(ce0a100, 97cb780, ea293d6c, 1)
    libzpool.so.1`zap_lockdir+0x1a0(8aaa3c0, 1, 0, 97cb780, 1, 1)
    libzpool.so.1`zap_remove_norm+0x30(8aaa3c0, 1, 0, 8728b10, 0, 97cb780)
    libzpool.so.1`zap_remove+0x29(8aaa3c0, 1, 0, 8728b10, 97cb780, a)
    ztest_replay_remove+0x225(ea294588, 8728ae8, 0, 38010000, 0, 0)
    ztest_remove+0x9f(ea294588, ea293f50, 4, 3)
    ztest_object_init+0x78(ea294588, ea293f50, 4e0, 1)
    ztest_dmu_object_alloc_free+0x71(ea294588, 13)
    ztest_dmu_objset_create_destroy+0x224(80cef08, 13, 0, 805d36c, 9017ad44, 0)
    ztest_execute+0x89(a, 807c720, 13, 0)
    ztest_thread+0xea(13, 0, 0, 0)
    libc.so.1`_thrp_setup+0x88(f0983240)
    libc.so.1`_lwp_start(f0983240, 0, 0, 0, 0, 0)
    Looking into it a bit, we see that this is an embedded blockpointer, so
    BP_GET_NDVAS should have returned 0:
         b32b240::blkptr
    EMBEDDED [L0 ZAP_OTHER] et=0 LZ4 size=200L/4aP birth=80L
    Instead, it looks like another thread is modifying this blockpointer:
         b32b240::ugrep | ::whatis
    f47a0e0c is in [ stack tid=0x19f ]
    ebd6ec40 is in [ stack tid=0x226 ]
    ea293bd0 is in [ stack tid=0x244 ]
    ea293be4 is in [ stack tid=0x244 ]
  
  Reviewed by: Prakash Surya <prakash.surya at delphix.com>
  Reviewed by: George Wilson <george.wilson at delphix.com>
  Approved by: Robert Mustacchi <rm at joyent.com>
  Author: Matthew Ahrens <mahrens at delphix.com>

Modified:
  head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
Directory Properties:
  head/sys/cddl/contrib/opensolaris/   (props changed)

Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c	Sat Sep  3 08:42:12 2016	(r305324)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c	Sat Sep  3 08:43:43 2016	(r305325)
@@ -1662,7 +1662,20 @@ dbuf_dirty(dmu_buf_impl_t *db, dmu_tx_t 
 		dnode_setdirty(dn, tx);
 		DB_DNODE_EXIT(db);
 		return (dr);
-	} else if (do_free_accounting) {
+	}
+
+	/*
+	 * The dn_struct_rwlock prevents db_blkptr from changing
+	 * due to a write from syncing context completing
+	 * while we are running, so we want to acquire it before
+	 * looking at db_blkptr.
+	 */
+	if (!RW_WRITE_HELD(&dn->dn_struct_rwlock)) {
+		rw_enter(&dn->dn_struct_rwlock, RW_READER);
+		drop_struct_lock = TRUE;
+	}
+
+	if (do_free_accounting) {
 		blkptr_t *bp = db->db_blkptr;
 		int64_t willfree = (bp && !BP_IS_HOLE(bp)) ?
 		    bp_get_dsize(os->os_spa, bp) : db->db.db_size;
@@ -1678,11 +1691,6 @@ dbuf_dirty(dmu_buf_impl_t *db, dmu_tx_t 
 		dnode_willuse_space(dn, -willfree, tx);
 	}
 
-	if (!RW_WRITE_HELD(&dn->dn_struct_rwlock)) {
-		rw_enter(&dn->dn_struct_rwlock, RW_READER);
-		drop_struct_lock = TRUE;
-	}
-
 	if (db->db_level == 0) {
 		dnode_new_blkid(dn, db->db_blkid, tx, drop_struct_lock);
 		ASSERT(dn->dn_maxblkid >= db->db_blkid);