freebsd-dev/module/zfs/mmp.c
Olaf Faaland d410c6d9fd Reimplement vdev_random_leaf and rename it
Rename it as mmp_random_leaf() since it is defined in mmp.c.

The earlier implementation could end up spinning forever if a pool had a
vdev marked writeable, none of whose children were writeable.  It also
did not guarantee that if a writeable leaf vdev existed, it would be
found.

Reimplement to recursively walk the device tree to select the leaf.  It
searches the entire tree, so that a return value of (NULL) indicates
there were no usable leaves in the pool; all were either not writeable
or had pending mmp writes.

It still chooses the starting child randomly at each level of the tree,
so if the pool's devices are healthy, the mmp writes go to random leaves
with an even distribution.  This was verified by testing using
zfs_multihost_history enabled.

Reviewed by: Thomas Caputi <tcaputi@datto.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes #6631 
Closes #6665
2017-09-22 14:29:26 -07:00

516 lines
16 KiB
C

/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
*/
#include <sys/abd.h>
#include <sys/mmp.h>
#include <sys/spa.h>
#include <sys/spa_impl.h>
#include <sys/vdev.h>
#include <sys/vdev_impl.h>
#include <sys/zfs_context.h>
#include <sys/callb.h>
/*
* Multi-Modifier Protection (MMP) attempts to prevent a user from importing
* or opening a pool on more than one host at a time. In particular, it
* prevents "zpool import -f" on a host from succeeding while the pool is
* already imported on another host. There are many other ways in which a
* device could be used by two hosts for different purposes at the same time
* resulting in pool damage. This implementation does not attempt to detect
* those cases.
*
* MMP operates by ensuring there are frequent visible changes on disk (a
* "heartbeat") at all times. And by altering the import process to check
* for these changes and failing the import when they are detected. This
* functionality is enabled by setting the 'multihost' pool property to on.
*
* Uberblocks written by the txg_sync thread always go into the first
* (N-MMP_BLOCKS_PER_LABEL) slots, the remaining slots are reserved for MMP.
* They are used to hold uberblocks which are exactly the same as the last
* synced uberblock except that the ub_timestamp is frequently updated.
* Like all other uberblocks, the slot is written with an embedded checksum,
* and slots with invalid checksums are ignored. This provides the
* "heartbeat", with no risk of overwriting good uberblocks that must be
* preserved, e.g. previous txgs and associated block pointers.
*
* Two optional fields are added to uberblock structure: ub_mmp_magic and
* ub_mmp_delay. The magic field allows zfs to tell whether ub_mmp_delay is
* valid. The delay field is a decaying average of the amount of time between
* completion of successive MMP writes, in nanoseconds. It is used to predict
* how long the import must wait to detect activity in the pool, before
* concluding it is not in use.
*
* During import an activity test may now be performed to determine if
* the pool is in use. The activity test is typically required if the
* ZPOOL_CONFIG_HOSTID does not match the system hostid, the pool state is
* POOL_STATE_ACTIVE, and the pool is not a root pool.
*
* The activity test finds the "best" uberblock (highest txg & timestamp),
* waits some time, and then finds the "best" uberblock again. If the txg
* and timestamp in both "best" uberblocks do not match, the pool is in use
* by another host and the import fails. Since the granularity of the
* timestamp is in seconds this activity test must take a bare minimum of one
* second. In order to assure the accuracy of the activity test, the default
* values result in an activity test duration of 10x the mmp write interval.
*
* The "zpool import" activity test can be expected to take a minimum time of
* zfs_multihost_import_intervals * zfs_multihost_interval milliseconds. If the
* "best" uberblock has a valid ub_mmp_delay field, then the duration of the
* test may take longer if MMP writes were occurring less frequently than
* expected. Additionally, the duration is then extended by a random 25% to
* attempt to to detect simultaneous imports. For example, if both partner
* hosts are rebooted at the same time and automatically attempt to import the
* pool.
*/
/*
* Used to control the frequency of mmp writes which are performed when the
* 'multihost' pool property is on. This is one factor used to determine the
* length of the activity check during import.
*
* The mmp write period is zfs_multihost_interval / leaf-vdevs milliseconds.
* This means that on average an mmp write will be issued for each leaf vdev
* every zfs_multihost_interval milliseconds. In practice, the observed period
* can vary with the I/O load and this observed value is the delay which is
* stored in the uberblock. The minimum allowed value is 100 ms.
*/
ulong_t zfs_multihost_interval = MMP_DEFAULT_INTERVAL;
/*
* Used to control the duration of the activity test on import. Smaller values
* of zfs_multihost_import_intervals will reduce the import time but increase
* the risk of failing to detect an active pool. The total activity check time
* is never allowed to drop below one second. A value of 0 is ignored and
* treated as if it was set to 1.
*/
uint_t zfs_multihost_import_intervals = MMP_DEFAULT_IMPORT_INTERVALS;
/*
* Controls the behavior of the pool when mmp write failures are detected.
*
* When zfs_multihost_fail_intervals = 0 then mmp write failures are ignored.
* The failures will still be reported to the ZED which depending on its
* configuration may take action such as suspending the pool or taking a
* device offline.
*
* When zfs_multihost_fail_intervals > 0 then sequential mmp write failures will
* cause the pool to be suspended. This occurs when
* zfs_multihost_fail_intervals * zfs_multihost_interval milliseconds have
* passed since the last successful mmp write. This guarantees the activity
* test will see mmp writes if the
* pool is imported.
*/
uint_t zfs_multihost_fail_intervals = MMP_DEFAULT_FAIL_INTERVALS;
static void mmp_thread(void *arg);
void
mmp_init(spa_t *spa)
{
mmp_thread_t *mmp = &spa->spa_mmp;
mutex_init(&mmp->mmp_thread_lock, NULL, MUTEX_DEFAULT, NULL);
cv_init(&mmp->mmp_thread_cv, NULL, CV_DEFAULT, NULL);
mutex_init(&mmp->mmp_io_lock, NULL, MUTEX_DEFAULT, NULL);
}
void
mmp_fini(spa_t *spa)
{
mmp_thread_t *mmp = &spa->spa_mmp;
mutex_destroy(&mmp->mmp_thread_lock);
cv_destroy(&mmp->mmp_thread_cv);
mutex_destroy(&mmp->mmp_io_lock);
}
static void
mmp_thread_enter(mmp_thread_t *mmp, callb_cpr_t *cpr)
{
CALLB_CPR_INIT(cpr, &mmp->mmp_thread_lock, callb_generic_cpr, FTAG);
mutex_enter(&mmp->mmp_thread_lock);
}
static void
mmp_thread_exit(mmp_thread_t *mmp, kthread_t **mpp, callb_cpr_t *cpr)
{
ASSERT(*mpp != NULL);
*mpp = NULL;
cv_broadcast(&mmp->mmp_thread_cv);
CALLB_CPR_EXIT(cpr); /* drops &mmp->mmp_thread_lock */
thread_exit();
}
void
mmp_thread_start(spa_t *spa)
{
mmp_thread_t *mmp = &spa->spa_mmp;
if (spa_writeable(spa)) {
mutex_enter(&mmp->mmp_thread_lock);
if (!mmp->mmp_thread) {
dprintf("mmp_thread_start pool %s\n",
spa->spa_name);
mmp->mmp_thread = thread_create(NULL, 0, mmp_thread,
spa, 0, &p0, TS_RUN, defclsyspri);
}
mutex_exit(&mmp->mmp_thread_lock);
}
}
void
mmp_thread_stop(spa_t *spa)
{
mmp_thread_t *mmp = &spa->spa_mmp;
mutex_enter(&mmp->mmp_thread_lock);
mmp->mmp_thread_exiting = 1;
cv_broadcast(&mmp->mmp_thread_cv);
while (mmp->mmp_thread) {
cv_wait(&mmp->mmp_thread_cv, &mmp->mmp_thread_lock);
}
mutex_exit(&mmp->mmp_thread_lock);
ASSERT(mmp->mmp_thread == NULL);
mmp->mmp_thread_exiting = 0;
}
/*
* Choose a leaf vdev to write an MMP block to. It must not have an
* outstanding mmp write (if so then there is a problem, and a new write will
* also block). If there is no usable leaf in this subtree return NULL,
* otherwise return a pointer to the leaf.
*
* When walking the subtree, a random child is chosen as the starting point so
* that when the tree is healthy, the leaf chosen will be random with even
* distribution. If there are unhealthy vdevs in the tree, the distribution
* will be really poor only if a large proportion of the vdevs are unhealthy,
* in which case there are other more pressing problems.
*/
static vdev_t *
mmp_random_leaf(vdev_t *vd)
{
int child_idx;
if (!vdev_writeable(vd))
return (NULL);
if (vd->vdev_ops->vdev_op_leaf)
return (vd->vdev_mmp_pending == 0 ? vd : NULL);
child_idx = spa_get_random(vd->vdev_children);
for (int offset = vd->vdev_children; offset > 0; offset--) {
vdev_t *leaf;
vdev_t *child = vd->vdev_child[(child_idx + offset) %
vd->vdev_children];
leaf = mmp_random_leaf(child);
if (leaf)
return (leaf);
}
return (NULL);
}
static void
mmp_write_done(zio_t *zio)
{
spa_t *spa = zio->io_spa;
vdev_t *vd = zio->io_vd;
mmp_thread_t *mts = zio->io_private;
mutex_enter(&mts->mmp_io_lock);
vd->vdev_mmp_pending = 0;
if (zio->io_error)
goto unlock;
/*
* Mmp writes are queued on a fixed schedule, but under many
* circumstances, such as a busy device or faulty hardware,
* the writes will complete at variable, much longer,
* intervals. In these cases, another node checking for
* activity must wait longer to account for these delays.
*
* The mmp_delay is calculated as a decaying average of the interval
* between completed mmp writes. This is used to predict how long
* the import must wait to detect activity in the pool, before
* concluding it is not in use.
*
* Do not set mmp_delay if the multihost property is not on,
* so as not to trigger an activity check on import.
*/
if (spa_multihost(spa)) {
hrtime_t delay = gethrtime() - mts->mmp_last_write;
if (delay > mts->mmp_delay)
mts->mmp_delay = delay;
else
mts->mmp_delay = (delay + mts->mmp_delay * 127) /
128;
} else {
mts->mmp_delay = 0;
}
mts->mmp_last_write = gethrtime();
unlock:
mutex_exit(&mts->mmp_io_lock);
spa_config_exit(spa, SCL_STATE, FTAG);
abd_free(zio->io_abd);
}
/*
* When the uberblock on-disk is updated by a spa_sync,
* creating a new "best" uberblock, update the one stored
* in the mmp thread state, used for mmp writes.
*/
void
mmp_update_uberblock(spa_t *spa, uberblock_t *ub)
{
mmp_thread_t *mmp = &spa->spa_mmp;
mutex_enter(&mmp->mmp_io_lock);
mmp->mmp_ub = *ub;
mmp->mmp_ub.ub_timestamp = gethrestime_sec();
mutex_exit(&mmp->mmp_io_lock);
}
/*
* Choose a random vdev, label, and MMP block, and write over it
* with a copy of the last-synced uberblock, whose timestamp
* has been updated to reflect that the pool is in use.
*/
static void
mmp_write_uberblock(spa_t *spa)
{
int flags = ZIO_FLAG_CONFIG_WRITER | ZIO_FLAG_CANFAIL;
mmp_thread_t *mmp = &spa->spa_mmp;
uberblock_t *ub;
vdev_t *vd;
int label;
uint64_t offset;
spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
vd = mmp_random_leaf(spa->spa_root_vdev);
if (vd == NULL) {
spa_config_exit(spa, SCL_STATE, FTAG);
return;
}
mutex_enter(&mmp->mmp_io_lock);
if (mmp->mmp_zio_root == NULL)
mmp->mmp_zio_root = zio_root(spa, NULL, NULL,
flags | ZIO_FLAG_GODFATHER);
ub = &mmp->mmp_ub;
ub->ub_timestamp = gethrestime_sec();
ub->ub_mmp_magic = MMP_MAGIC;
ub->ub_mmp_delay = mmp->mmp_delay;
vd->vdev_mmp_pending = gethrtime();
zio_t *zio = zio_null(mmp->mmp_zio_root, spa, NULL, NULL, NULL, flags);
abd_t *ub_abd = abd_alloc_for_io(VDEV_UBERBLOCK_SIZE(vd), B_TRUE);
abd_zero(ub_abd, VDEV_UBERBLOCK_SIZE(vd));
abd_copy_from_buf(ub_abd, ub, sizeof (uberblock_t));
mutex_exit(&mmp->mmp_io_lock);
offset = VDEV_UBERBLOCK_OFFSET(vd, VDEV_UBERBLOCK_COUNT(vd) -
MMP_BLOCKS_PER_LABEL + spa_get_random(MMP_BLOCKS_PER_LABEL));
label = spa_get_random(VDEV_LABELS);
vdev_label_write(zio, vd, label, ub_abd, offset,
VDEV_UBERBLOCK_SIZE(vd), mmp_write_done, mmp,
flags | ZIO_FLAG_DONT_PROPAGATE);
spa_mmp_history_add(ub->ub_txg, ub->ub_timestamp, ub->ub_mmp_delay, vd,
label);
zio_nowait(zio);
}
static void
mmp_thread(void *arg)
{
spa_t *spa = (spa_t *)arg;
mmp_thread_t *mmp = &spa->spa_mmp;
boolean_t last_spa_suspended = spa_suspended(spa);
boolean_t last_spa_multihost = spa_multihost(spa);
callb_cpr_t cpr;
hrtime_t max_fail_ns = zfs_multihost_fail_intervals *
MSEC2NSEC(MAX(zfs_multihost_interval, MMP_MIN_INTERVAL));
mmp_thread_enter(mmp, &cpr);
/*
* The mmp_write_done() function calculates mmp_delay based on the
* prior value of mmp_delay and the elapsed time since the last write.
* For the first mmp write, there is no "last write", so we start
* with fake, but reasonable, default non-zero values.
*/
mmp->mmp_delay = MSEC2NSEC(MAX(zfs_multihost_interval,
MMP_MIN_INTERVAL)) / MAX(vdev_count_leaves(spa), 1);
mmp->mmp_last_write = gethrtime() - mmp->mmp_delay;
while (!mmp->mmp_thread_exiting) {
uint64_t mmp_fail_intervals = zfs_multihost_fail_intervals;
uint64_t mmp_interval = MSEC2NSEC(
MAX(zfs_multihost_interval, MMP_MIN_INTERVAL));
boolean_t suspended = spa_suspended(spa);
boolean_t multihost = spa_multihost(spa);
hrtime_t start, next_time;
start = gethrtime();
if (multihost) {
next_time = start + mmp_interval /
MAX(vdev_count_leaves(spa), 1);
} else {
next_time = start + MSEC2NSEC(MMP_DEFAULT_INTERVAL);
}
/*
* When MMP goes off => on, or spa goes suspended =>
* !suspended, we know no writes occurred recently. We
* update mmp_last_write to give us some time to try.
*/
if ((!last_spa_multihost && multihost) ||
(last_spa_suspended && !suspended)) {
mutex_enter(&mmp->mmp_io_lock);
mmp->mmp_last_write = gethrtime();
mutex_exit(&mmp->mmp_io_lock);
} else if (last_spa_multihost && !multihost) {
mutex_enter(&mmp->mmp_io_lock);
mmp->mmp_delay = 0;
mutex_exit(&mmp->mmp_io_lock);
}
last_spa_multihost = multihost;
last_spa_suspended = suspended;
/*
* Smooth max_fail_ns when its factors are decreased, because
* making (max_fail_ns < mmp_interval) results in the pool being
* immediately suspended before writes can occur at the new
* higher frequency.
*/
if ((mmp_interval * mmp_fail_intervals) < max_fail_ns) {
max_fail_ns = ((31 * max_fail_ns) + (mmp_interval *
mmp_fail_intervals)) / 32;
} else {
max_fail_ns = mmp_interval * mmp_fail_intervals;
}
/*
* Suspend the pool if no MMP write has succeeded in over
* mmp_interval * mmp_fail_intervals nanoseconds.
*/
if (!suspended && mmp_fail_intervals && multihost &&
(start - mmp->mmp_last_write) > max_fail_ns) {
zio_suspend(spa, NULL);
}
if (multihost)
mmp_write_uberblock(spa);
CALLB_CPR_SAFE_BEGIN(&cpr);
(void) cv_timedwait_sig(&mmp->mmp_thread_cv,
&mmp->mmp_thread_lock, ddi_get_lbolt() +
((next_time - gethrtime()) / (NANOSEC / hz)));
CALLB_CPR_SAFE_END(&cpr, &mmp->mmp_thread_lock);
}
/* Outstanding writes are allowed to complete. */
if (mmp->mmp_zio_root)
zio_wait(mmp->mmp_zio_root);
mmp->mmp_zio_root = NULL;
mmp_thread_exit(mmp, &mmp->mmp_thread, &cpr);
}
/*
* Signal the MMP thread to wake it, when it is sleeping on
* its cv. Used when some module parameter has changed and
* we want the thread to know about it.
* Only signal if the pool is active and mmp thread is
* running, otherwise there is no thread to wake.
*/
static void
mmp_signal_thread(spa_t *spa)
{
mmp_thread_t *mmp = &spa->spa_mmp;
mutex_enter(&mmp->mmp_thread_lock);
if (mmp->mmp_thread)
cv_broadcast(&mmp->mmp_thread_cv);
mutex_exit(&mmp->mmp_thread_lock);
}
void
mmp_signal_all_threads(void)
{
spa_t *spa = NULL;
mutex_enter(&spa_namespace_lock);
while ((spa = spa_next(spa))) {
if (spa->spa_state == POOL_STATE_ACTIVE)
mmp_signal_thread(spa);
}
mutex_exit(&spa_namespace_lock);
}
#if defined(_KERNEL) && defined(HAVE_SPL)
#include <linux/mod_compat.h>
static int
param_set_multihost_interval(const char *val, zfs_kernel_param_t *kp)
{
int ret;
ret = param_set_ulong(val, kp);
if (ret < 0)
return (ret);
mmp_signal_all_threads();
return (ret);
}
/* BEGIN CSTYLED */
module_param(zfs_multihost_fail_intervals, uint, 0644);
MODULE_PARM_DESC(zfs_multihost_fail_intervals,
"Max allowed period without a successful mmp write");
module_param_call(zfs_multihost_interval, param_set_multihost_interval,
param_get_ulong, &zfs_multihost_interval, 0644);
MODULE_PARM_DESC(zfs_multihost_interval,
"Milliseconds between mmp writes to each leaf");
module_param(zfs_multihost_import_intervals, uint, 0644);
MODULE_PARM_DESC(zfs_multihost_import_intervals,
"Number of zfs_multihost_interval periods to wait for activity");
/* END CSTYLED */
#endif