Fix issues found with zfs diff

Two deadlocks / ASSERT failures were introduced in a2c2ed1b which
would occur whenever arc_buf_fill() failed to decrypt a block of
data. This occurred because the call to arc_buf_destroy() which
was responsible for cleaning up the newly created buffer would
attempt to take out the hdr lock that it was already holding. This
was resolved by calling the underlying functions directly without
retaking the lock.

In addition, the dmu_diff() code did not properly ensure that keys
were loaded and mapped before begining dataset traversal. It turns
out that this code does not need to look at any encrypted values,
so the code was altered to perform raw IO only.

Reviewed by: Matthew Ahrens <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Tom Caputi <[email protected]>
Closes #7354 
Closes #7456 

1 files changed, 15 insertions, 3 deletions

diff --git a/module/zfs/dmu_diff.c b/module/zfs/dmu_diff.c
index 982b96132..76c32b126 100644
--- a/module/zfs/dmu_diff.c
+++ b/module/zfs/dmu_diff.c
@@ -131,11 +131,14 @@ diff_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 		arc_buf_t *abuf;
 		arc_flags_t aflags = ARC_FLAG_WAIT;
 		int blksz = BP_GET_LSIZE(bp);
+		int zio_flags = ZIO_FLAG_CANFAIL;
 		int i;
 
+		if (BP_IS_PROTECTED(bp))
+			zio_flags |= ZIO_FLAG_RAW;
+
 		if (arc_read(NULL, spa, bp, arc_getbuf_func, &abuf,
-		    ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL,
-		    &aflags, zb) != 0)
+		    ZIO_PRIORITY_ASYNC_READ, zio_flags, &aflags, zb) != 0)
 			return (SET_ERROR(EIO));
 
 		blk = abuf->b_data;
@@ -206,8 +209,17 @@ dmu_diff(const char *tosnap_name, const char *fromsnap_name,
 	da.da_ddr.ddr_first = da.da_ddr.ddr_last = 0;
 	da.da_err = 0;
 
+	/*
+	 * Since zfs diff only looks at dnodes which are stored in plaintext
+	 * (other than bonus buffers), we don't technically need to decrypt
+	 * the dataset to perform this operation. However, the command line
+	 * utility will still fail if the keys are not loaded because the
+	 * dataset isn't mounted and because it will fail when it attempts to
+	 * call the ZFS_IOC_OBJ_TO_STATS ioctl.
+	 */
 	error = traverse_dataset(tosnap, fromtxg,
-	    TRAVERSE_PRE | TRAVERSE_PREFETCH_METADATA, diff_cb, &da);
+	    TRAVERSE_PRE | TRAVERSE_PREFETCH_METADATA | TRAVERSE_NO_DECRYPT,
+	    diff_cb, &da);
 
 	if (error != 0) {
 		da.da_err = error;