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panic in removal_remap test on 4K devices

If the zfs_remove_max_segment tunable is changed to be not a multiple of
the sector size, then the device removal code will malfunction and try
to create mappings that are smaller than one sector, leading to a panic.

On debug bits this assertion will fail in spa_vdev_copy_segment():
    ASSERT3U(DVA_GET_ASIZE(&dst), ==, size);

On nondebug, the system panics with a stack like:
    metaslab_free_concrete()
    metaslab_free_impl()
    metaslab_free_impl_cb()
    vdev_indirect_remap()
    free_from_removing_vdev()
    metaslab_free_impl()
    metaslab_free_dva()
    metaslab_free()

Fortunately, the default for zfs_remove_max_segment is 1MB, so this
can't occur by default.  We hit it during this test because
removal_remap.ksh changes zfs_remove_max_segment to 1KB. When testing on
4KB-sector disks, we hit the bug.

This change makes the zfs_remove_max_segment tunable more robust,
automatically rounding it up to a multiple of the sector size. We also
turn some key assertions into VERIFY's so that similar bugs would be
caught before they are encoded on disk (and thus avoid a
panic-reboot-loop).

Reviewed-by: Sean Eric Fagan <sef@ixsystems.com>
Reviewed-by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Reviewed-by: Sebastien Roy <sebastien.roy@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
External-issue: DLPX-61342
Closes #8893
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ahrens authored and tonyhutter committed Jun 13, 2019
1 parent cc7e342 commit 305c681f44557d41b223bd6f839569915b52f358
Showing with 59 additions and 14 deletions.
  1. +4 −4 include/sys/vdev_removal.h
  2. +27 −0 man/man5/zfs-module-parameters.5
  3. +2 −3 module/zfs/vdev_label.c
  4. +26 −7 module/zfs/vdev_removal.c
@@ -14,7 +14,7 @@
*/

/*
* Copyright (c) 2014, 2017 by Delphix. All rights reserved.
* Copyright (c) 2014, 2019 by Delphix. All rights reserved.
*/

#ifndef _SYS_VDEV_REMOVAL_H
@@ -81,13 +81,13 @@ extern void spa_vdev_condense_suspend(spa_t *);
extern int spa_vdev_remove(spa_t *, uint64_t, boolean_t);
extern void free_from_removing_vdev(vdev_t *, uint64_t, uint64_t);
extern int spa_removal_get_stats(spa_t *, pool_removal_stat_t *);
extern void svr_sync(spa_t *spa, dmu_tx_t *tx);
extern void svr_sync(spa_t *, dmu_tx_t *);
extern void spa_vdev_remove_suspend(spa_t *);
extern int spa_vdev_remove_cancel(spa_t *);
extern void spa_vdev_removal_destroy(spa_vdev_removal_t *svr);
extern void spa_vdev_removal_destroy(spa_vdev_removal_t *);
extern uint64_t spa_remove_max_segment(spa_t *);

extern int vdev_removal_max_span;
extern int zfs_remove_max_segment;

#ifdef __cplusplus
}
@@ -2194,6 +2194,33 @@ pool cannot be returned to a healthy state prior to removing the device.
Default value: \fB0\fR.
.RE

.sp
.ne 2
.na
\fBzfs_removal_suspend_progress\fR (int)
.ad
.RS 12n
.sp
This is used by the test suite so that it can ensure that certain actions
happen while in the middle of a removal.
.sp
Default value: \fB0\fR.
.RE

.sp
.ne 2
.na
\fBzfs_remove_max_segment\fR (int)
.ad
.RS 12n
.sp
The largest contiguous segment that we will attempt to allocate when removing
a device. This can be no larger than 16MB. If there is a performance
problem with attempting to allocate large blocks, consider decreasing this.
.sp
Default value: \fB16,777,216\fR (16MB).
.RE

.sp
.ne 2
.na
@@ -21,8 +21,7 @@

/*
* Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2012, 2018 by Delphix. All rights reserved.
* Copyright (c) 2012, 2016 by Delphix. All rights reserved.
* Copyright (c) 2012, 2019 by Delphix. All rights reserved.
* Copyright (c) 2017, Intel Corporation.
*/

@@ -613,7 +612,7 @@ vdev_config_generate(spa_t *spa, vdev_t *vd, boolean_t getstats,
* zfs_remove_max_segment, so we need at least one entry
* per zfs_remove_max_segment of allocated data.
*/
seg_count += to_alloc / zfs_remove_max_segment;
seg_count += to_alloc / spa_remove_max_segment(spa);

fnvlist_add_uint64(nv, ZPOOL_CONFIG_INDIRECT_SIZE,
seg_count *
@@ -21,7 +21,7 @@

/*
* Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2011, 2018 by Delphix. All rights reserved.
* Copyright (c) 2011, 2019 by Delphix. All rights reserved.
*/

#include <sys/zfs_context.h>
@@ -100,6 +100,8 @@ int zfs_remove_max_copy_bytes = 64 * 1024 * 1024;
* removing a device. This can be no larger than SPA_MAXBLOCKSIZE. If
* there is a performance problem with attempting to allocate large blocks,
* consider decreasing this.
*
* See also the accessor function spa_remove_max_segment().
*/
int zfs_remove_max_segment = SPA_MAXBLOCKSIZE;

@@ -951,8 +953,10 @@ spa_vdev_copy_segment(vdev_t *vd, range_tree_t *segs,
vdev_indirect_mapping_entry_t *entry;
dva_t dst = {{ 0 }};
uint64_t start = range_tree_min(segs);
ASSERT0(P2PHASE(start, 1 << spa->spa_min_ashift));

ASSERT3U(maxalloc, <=, SPA_MAXBLOCKSIZE);
ASSERT0(P2PHASE(maxalloc, 1 << spa->spa_min_ashift));

uint64_t size = range_tree_span(segs);
if (range_tree_span(segs) > maxalloc) {
@@ -983,6 +987,7 @@ spa_vdev_copy_segment(vdev_t *vd, range_tree_t *segs,
}
}
ASSERT3U(size, <=, maxalloc);
ASSERT0(P2PHASE(size, 1 << spa->spa_min_ashift));

/*
* An allocation class might not have any remaining vdevs or space
@@ -1026,11 +1031,11 @@ spa_vdev_copy_segment(vdev_t *vd, range_tree_t *segs,

/*
* We can't have any padding of the allocated size, otherwise we will
* misunderstand what's allocated, and the size of the mapping.
* The caller ensures this will be true by passing in a size that is
* aligned to the worst (highest) ashift in the pool.
* misunderstand what's allocated, and the size of the mapping. We
* prevent padding by ensuring that all devices in the pool have the
* same ashift, and the allocation size is a multiple of the ashift.
*/
ASSERT3U(DVA_GET_ASIZE(&dst), ==, size);
VERIFY3U(DVA_GET_ASIZE(&dst), ==, size);

entry = kmem_zalloc(sizeof (vdev_indirect_mapping_entry_t), KM_SLEEP);
DVA_MAPPING_SET_SRC_OFFSET(&entry->vime_mapping, start);
@@ -1363,6 +1368,20 @@ spa_vdev_copy_impl(vdev_t *vd, spa_vdev_removal_t *svr, vdev_copy_arg_t *vca,
range_tree_destroy(segs);
}

/*
* The size of each removal mapping is limited by the tunable
* zfs_remove_max_segment, but we must adjust this to be a multiple of the
* pool's ashift, so that we don't try to split individual sectors regardless
* of the tunable value. (Note that device removal requires that all devices
* have the same ashift, so there's no difference between spa_min_ashift and
* spa_max_ashift.) The raw tunable should not be used elsewhere.
*/
uint64_t
spa_remove_max_segment(spa_t *spa)
{
return (P2ROUNDUP(zfs_remove_max_segment, 1 << spa->spa_max_ashift));
}

/*
* The removal thread operates in open context. It iterates over all
* allocated space in the vdev, by loading each metaslab's spacemap.
@@ -1385,7 +1404,7 @@ spa_vdev_remove_thread(void *arg)
spa_t *spa = arg;
spa_vdev_removal_t *svr = spa->spa_vdev_removal;
vdev_copy_arg_t vca;
uint64_t max_alloc = zfs_remove_max_segment;
uint64_t max_alloc = spa_remove_max_segment(spa);
uint64_t last_txg = 0;

spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
@@ -1511,7 +1530,7 @@ spa_vdev_remove_thread(void *arg)
vd = vdev_lookup_top(spa, svr->svr_vdev_id);

if (txg != last_txg)
max_alloc = zfs_remove_max_segment;
max_alloc = spa_remove_max_segment(spa);
last_txg = txg;

spa_vdev_copy_impl(vd, svr, &vca, &max_alloc, tx);

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