Fix L2ARC reads when compressed ARC disabled

When reading compressed blocks from the L2ARC, with
compressed ARC disabled, arc_hdr_size() returns
LSIZE rather than PSIZE, but the actual read is PSIZE.
This causes l2arc_read_done() to compare the checksum
against the wrong size, resulting in checksum failure.

This manifests as an increase in the kstat l2_cksum_bad
and the read being retried from the main pool, making the
L2ARC ineffective.

Add new L2ARC tests with Compressed ARC enabled/disabled

Blocks are handled differently depending on the state of the
zfs_compressed_arc_enabled tunable.

If a block is compressed on-disk, and compressed_arc is enabled:
- the block is read from disk
- It is NOT decompressed
- It is added to the ARC in its compressed form
- l2arc_write_buffers() may write it to the L2ARC (as is)
- l2arc_read_done() compares the checksum to the BP (compressed)

However, if compressed_arc is disabled:
- the block is read from disk
- It is decompressed
- It is added to the ARC (uncompressed)
- l2arc_write_buffers() will use l2arc_apply_transforms() to
  recompress the block, before writing it to the L2ARC
- l2arc_read_done() compares the checksum to the BP (compressed)
- l2arc_read_done() will use l2arc_untransform() to uncompress it

This test writes out a test file to a pool consisting of one disk
and one cache device, then randomly reads from it. Since the arc_max
in the tests is low, this will feed the L2ARC, and result in reads
from the L2ARC.

We compare the value of the kstat l2_cksum_bad before and after
to determine if any blocks failed to survive the trip through the
L2ARC.

Sponsored-by: The FreeBSD Foundation
Signed-off-by: Allan Jude <allanjude@freebsd.org>

module/zfs/arc.c

@@ -28,6 +28,10 @@
  * Copyright (c) 2020, George Amanakis. All rights reserved.
  * Copyright (c) 2019, Klara Inc.
  * Copyright (c) 2019, Allan Jude
+ * Copyright (c) 2020, The FreeBSD Foundation [1]
+ *
+ * [1] Portions of this software were developed by Allan Jude
+ *     under sponsorship from the FreeBSD Foundation.
  */
 
 /*
@@ -6150,6 +6154,17 @@ arc_read(zio_t *pio, spa_t *spa, const blkptr_t *bp,
 				cb->l2rcb_zb = *zb;
 				cb->l2rcb_flags = zio_flags;
 
+				/*
+				 * When Compressed ARC is disabled, but the
+				 * L2ARC block is compressed, arc_hdr_size()
+				 * will have returned LSIZE rather than PSIZE.
+				 */
+				if (HDR_GET_COMPRESS(hdr) != ZIO_COMPRESS_OFF &&
+				    !HDR_COMPRESSION_ENABLED(hdr) &&
+				    HDR_GET_PSIZE(hdr) != 0) {
+					size = HDR_GET_PSIZE(hdr);
+				}
+
 				asize = vdev_psize_to_asize(vd, size);
 				if (asize != size) {
 					abd = abd_alloc_for_io(asize,

tests/runfiles/common.run

@@ -538,7 +538,8 @@ tags = ['functional', 'cli_user', 'zpool_status']
 
 [tests/functional/compression]
 tests = ['compress_001_pos', 'compress_002_pos', 'compress_003_pos',
-    'l2arc_encrypted', 'l2arc_encrypted_no_compressed_arc']
+    'l2arc_encrypted', 'l2arc_encrypted_no_compressed_arc',
+    'l2arc_compressed_arc', 'l2arc_compressed_arc_disabled']
 tags = ['functional', 'compression']
 
 [tests/functional/cp_files]

tests/zfs-tests/tests/functional/compression/l2arc_compressed_arc.ksh

@@ -0,0 +1,97 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2020 The FreeBSD Foundation [1]
+#
+# [1] Portions of this software were developed by Allan Jude
+#     under sponsorship from the FreeBSD Foundation.
+
+. $STF_SUITE/include/libtest.shlib
+
+export SIZE=1G
+export VDIR=$TESTDIR/disk.persist_l2arc
+export VDEV="$VDIR/a"
+export VDEV_CACHE="$VDIR/b"
+
+# fio options
+export DIRECTORY=/$TESTPOOL-l2arc
+export NUMJOBS=4
+export RUNTIME=30
+export PERF_RANDSEED=1234
+export PERF_COMPPERCENT=66
+export PERF_COMPCHUNK=0
+export BLOCKSIZE=128K
+export SYNC_TYPE=0
+export DIRECT=1
+
+#
+# DESCRIPTION:
+#	System with compressed_arc disabled succeeds at reading from L2ARC
+#
+# STRATEGY:
+#	1. Enable compressed_arc.
+#	2. Create pool with a cache device and compression enabled.
+#	3. Read the number of L2ARC checksum failures.
+#	4. Create a random file in that pool and random read for 30 sec.
+#	5. Read the number of L2ARC checksum failures.
+#
+
+verify_runnable "global"
+
+log_assert "L2ARC with compressed_arc enabled succeeds."
+
+origin_carc_setting=$(get_tunable COMPRESSED_ARC_ENABLED)
+
+function cleanup
+{
+	if poolexists $TESTPOOL-l2arc ; then
+		destroy_pool $TESTPOOL-l2arc
+	fi
+
+	log_must set_tunable64 COMPRESSED_ARC_ENABLED $origin_carc_setting
+}
+log_onexit cleanup
+
+# Enable Compressed ARC so that in-ARC and on-disk will match
+log_must set_tunable64 COMPRESSED_ARC_ENABLED 1
+
+log_must rm -rf $VDIR
+log_must mkdir -p $VDIR
+log_must mkfile $SIZE $VDEV
+
+typeset fill_mb=800
+typeset cache_sz=$(( floor($fill_mb / 2) ))
+export FILE_SIZE=$(( floor($fill_mb / $NUMJOBS) ))M
+
+log_must truncate -s ${cache_sz}M $VDEV_CACHE
+
+log_must zpool create -O compression=lz4 -f $TESTPOOL-l2arc $VDEV cache $VDEV_CACHE
+
+l2_cksum_bad_start=$(get_arcstat l2_cksum_bad)
+
+log_must fio $FIO_SCRIPTS/mkfiles.fio
+log_must fio $FIO_SCRIPTS/random_reads.fio
+
+l2_cksum_bad_end=$(get_arcstat l2_cksum_bad)
+
+log_note "L2ARC Failed Checksums before: $l2_cksum_bad_start After:"\
+	"$l2_cksum_bad_end"
+log_must test $(( $l2_cksum_bad_end - $l2_cksum_bad_start )) -eq 0
+
+log_must zpool destroy -f $TESTPOOL-l2arc
+
+log_pass "L2ARC with compressed_arc enabled does not result in checksum errors."

tests/zfs-tests/tests/functional/compression/l2arc_compressed_arc_disabled.ksh

@@ -0,0 +1,98 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2020 The FreeBSD Foundation [1]
+#
+# [1] Portions of this software were developed by Allan Jude
+#     under sponsorship from the FreeBSD Foundation.
+
+. $STF_SUITE/include/libtest.shlib
+
+export SIZE=1G
+export VDIR=$TESTDIR/disk.persist_l2arc
+export VDEV="$VDIR/a"
+export VDEV_CACHE="$VDIR/b"
+
+# fio options
+export DIRECTORY=/$TESTPOOL-l2arc
+export NUMJOBS=4
+export RUNTIME=30
+export PERF_RANDSEED=1234
+export PERF_COMPPERCENT=66
+export PERF_COMPCHUNK=0
+export BLOCKSIZE=128K
+export SYNC_TYPE=0
+export DIRECT=1
+
+#
+# DESCRIPTION:
+#	System with compressed_arc disabled succeeds at reading from L2ARC
+#
+# STRATEGY:
+#	1. Disable compressed_arc.
+#	2. Create pool with a cache device and compression enabled.
+#	3. Read the number of L2ARC checksum failures.
+#	4. Create a random file in that pool and random read for 30 sec.
+#	5. Read the number of L2ARC checksum failures.
+#
+
+verify_runnable "global"
+
+log_assert "L2ARC with compressed_arc disabled succeeds."
+
+origin_carc_setting=$(get_tunable COMPRESSED_ARC_ENABLED)
+
+function cleanup
+{
+	if poolexists $TESTPOOL-l2arc ; then
+		destroy_pool $TESTPOOL-l2arc
+	fi
+
+	log_must set_tunable64 COMPRESSED_ARC_ENABLED $origin_carc_setting
+}
+log_onexit cleanup
+
+log_must rm -rf $VDIR
+log_must mkdir -p $VDIR
+log_must mkfile $SIZE $VDEV
+
+# Disable Compressed ARC so that in-ARC and on-disk will not match
+log_must set_tunable64 COMPRESSED_ARC_ENABLED 0
+
+typeset fill_mb=800
+typeset cache_sz=$(( floor($fill_mb / 2) ))
+export FILE_SIZE=$(( floor($fill_mb / $NUMJOBS) ))M
+
+log_must truncate -s ${cache_sz}M $VDEV_CACHE
+
+log_must zpool create -O compression=lz4 -f $TESTPOOL-l2arc $VDEV cache $VDEV_CACHE
+
+l2_cksum_bad_start=$(get_arcstat l2_cksum_bad)
+
+log_must fio $FIO_SCRIPTS/mkfiles.fio
+log_must fio $FIO_SCRIPTS/random_reads.fio
+
+l2_cksum_bad_end=$(get_arcstat l2_cksum_bad)
+
+log_note "L2ARC Failed Checksums before: $l2_cksum_bad_start After:"\
+	"$l2_cksum_bad_end"
+log_must test $(( $l2_cksum_bad_end - $l2_cksum_bad_start )) -eq 0
+
+log_must zpool destroy -f $TESTPOOL-l2arc
+
+log_pass "L2ARC with compressed_arc disabled does not result in checksum"\
+	"errors."