/
dm-mpath.c
1510 lines (1227 loc) · 33.6 KB
/
dm-mpath.c
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/*
* Copyright (C) 2003 Sistina Software Limited.
* Copyright (C) 2004-2005 Red Hat, Inc. All rights reserved.
*
* This file is released under the GPL.
*/
#include <linux/device-mapper.h>
#include "dm-path-selector.h"
#include "dm-bio-list.h"
#include "dm-bio-record.h"
#include "dm-uevent.h"
#include <linux/ctype.h>
#include <linux/init.h>
#include <linux/mempool.h>
#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/workqueue.h>
#include <scsi/scsi_dh.h>
#include <asm/atomic.h>
#define DM_MSG_PREFIX "multipath"
#define MESG_STR(x) x, sizeof(x)
/* Path properties */
struct pgpath {
struct list_head list;
struct priority_group *pg; /* Owning PG */
unsigned is_active; /* Path status */
unsigned fail_count; /* Cumulative failure count */
struct dm_path path;
struct work_struct deactivate_path;
};
#define path_to_pgpath(__pgp) container_of((__pgp), struct pgpath, path)
/*
* Paths are grouped into Priority Groups and numbered from 1 upwards.
* Each has a path selector which controls which path gets used.
*/
struct priority_group {
struct list_head list;
struct multipath *m; /* Owning multipath instance */
struct path_selector ps;
unsigned pg_num; /* Reference number */
unsigned bypassed; /* Temporarily bypass this PG? */
unsigned nr_pgpaths; /* Number of paths in PG */
struct list_head pgpaths;
};
/* Multipath context */
struct multipath {
struct list_head list;
struct dm_target *ti;
spinlock_t lock;
const char *hw_handler_name;
struct work_struct activate_path;
struct pgpath *pgpath_to_activate;
unsigned nr_priority_groups;
struct list_head priority_groups;
unsigned pg_init_required; /* pg_init needs calling? */
unsigned pg_init_in_progress; /* Only one pg_init allowed at once */
unsigned nr_valid_paths; /* Total number of usable paths */
struct pgpath *current_pgpath;
struct priority_group *current_pg;
struct priority_group *next_pg; /* Switch to this PG if set */
unsigned repeat_count; /* I/Os left before calling PS again */
unsigned queue_io; /* Must we queue all I/O? */
unsigned queue_if_no_path; /* Queue I/O if last path fails? */
unsigned saved_queue_if_no_path;/* Saved state during suspension */
unsigned pg_init_retries; /* Number of times to retry pg_init */
unsigned pg_init_count; /* Number of times pg_init called */
struct work_struct process_queued_ios;
struct bio_list queued_ios;
unsigned queue_size;
struct work_struct trigger_event;
/*
* We must use a mempool of dm_mpath_io structs so that we
* can resubmit bios on error.
*/
mempool_t *mpio_pool;
};
/*
* Context information attached to each bio we process.
*/
struct dm_mpath_io {
struct pgpath *pgpath;
struct dm_bio_details details;
};
typedef int (*action_fn) (struct pgpath *pgpath);
#define MIN_IOS 256 /* Mempool size */
static struct kmem_cache *_mpio_cache;
static struct workqueue_struct *kmultipathd, *kmpath_handlerd;
static void process_queued_ios(struct work_struct *work);
static void trigger_event(struct work_struct *work);
static void activate_path(struct work_struct *work);
static void deactivate_path(struct work_struct *work);
/*-----------------------------------------------
* Allocation routines
*-----------------------------------------------*/
static struct pgpath *alloc_pgpath(void)
{
struct pgpath *pgpath = kzalloc(sizeof(*pgpath), GFP_KERNEL);
if (pgpath) {
pgpath->is_active = 1;
INIT_WORK(&pgpath->deactivate_path, deactivate_path);
}
return pgpath;
}
static void free_pgpath(struct pgpath *pgpath)
{
kfree(pgpath);
}
static void deactivate_path(struct work_struct *work)
{
struct pgpath *pgpath =
container_of(work, struct pgpath, deactivate_path);
blk_abort_queue(pgpath->path.dev->bdev->bd_disk->queue);
}
static struct priority_group *alloc_priority_group(void)
{
struct priority_group *pg;
pg = kzalloc(sizeof(*pg), GFP_KERNEL);
if (pg)
INIT_LIST_HEAD(&pg->pgpaths);
return pg;
}
static void free_pgpaths(struct list_head *pgpaths, struct dm_target *ti)
{
unsigned long flags;
struct pgpath *pgpath, *tmp;
struct multipath *m = ti->private;
list_for_each_entry_safe(pgpath, tmp, pgpaths, list) {
list_del(&pgpath->list);
if (m->hw_handler_name)
scsi_dh_detach(bdev_get_queue(pgpath->path.dev->bdev));
dm_put_device(ti, pgpath->path.dev);
spin_lock_irqsave(&m->lock, flags);
if (m->pgpath_to_activate == pgpath)
m->pgpath_to_activate = NULL;
spin_unlock_irqrestore(&m->lock, flags);
free_pgpath(pgpath);
}
}
static void free_priority_group(struct priority_group *pg,
struct dm_target *ti)
{
struct path_selector *ps = &pg->ps;
if (ps->type) {
ps->type->destroy(ps);
dm_put_path_selector(ps->type);
}
free_pgpaths(&pg->pgpaths, ti);
kfree(pg);
}
static struct multipath *alloc_multipath(struct dm_target *ti)
{
struct multipath *m;
m = kzalloc(sizeof(*m), GFP_KERNEL);
if (m) {
INIT_LIST_HEAD(&m->priority_groups);
spin_lock_init(&m->lock);
m->queue_io = 1;
INIT_WORK(&m->process_queued_ios, process_queued_ios);
INIT_WORK(&m->trigger_event, trigger_event);
INIT_WORK(&m->activate_path, activate_path);
m->mpio_pool = mempool_create_slab_pool(MIN_IOS, _mpio_cache);
if (!m->mpio_pool) {
kfree(m);
return NULL;
}
m->ti = ti;
ti->private = m;
}
return m;
}
static void free_multipath(struct multipath *m)
{
struct priority_group *pg, *tmp;
list_for_each_entry_safe(pg, tmp, &m->priority_groups, list) {
list_del(&pg->list);
free_priority_group(pg, m->ti);
}
kfree(m->hw_handler_name);
mempool_destroy(m->mpio_pool);
kfree(m);
}
/*-----------------------------------------------
* Path selection
*-----------------------------------------------*/
static void __switch_pg(struct multipath *m, struct pgpath *pgpath)
{
m->current_pg = pgpath->pg;
/* Must we initialise the PG first, and queue I/O till it's ready? */
if (m->hw_handler_name) {
m->pg_init_required = 1;
m->queue_io = 1;
} else {
m->pg_init_required = 0;
m->queue_io = 0;
}
m->pg_init_count = 0;
}
static int __choose_path_in_pg(struct multipath *m, struct priority_group *pg)
{
struct dm_path *path;
path = pg->ps.type->select_path(&pg->ps, &m->repeat_count);
if (!path)
return -ENXIO;
m->current_pgpath = path_to_pgpath(path);
if (m->current_pg != pg)
__switch_pg(m, m->current_pgpath);
return 0;
}
static void __choose_pgpath(struct multipath *m)
{
struct priority_group *pg;
unsigned bypassed = 1;
if (!m->nr_valid_paths)
goto failed;
/* Were we instructed to switch PG? */
if (m->next_pg) {
pg = m->next_pg;
m->next_pg = NULL;
if (!__choose_path_in_pg(m, pg))
return;
}
/* Don't change PG until it has no remaining paths */
if (m->current_pg && !__choose_path_in_pg(m, m->current_pg))
return;
/*
* Loop through priority groups until we find a valid path.
* First time we skip PGs marked 'bypassed'.
* Second time we only try the ones we skipped.
*/
do {
list_for_each_entry(pg, &m->priority_groups, list) {
if (pg->bypassed == bypassed)
continue;
if (!__choose_path_in_pg(m, pg))
return;
}
} while (bypassed--);
failed:
m->current_pgpath = NULL;
m->current_pg = NULL;
}
/*
* Check whether bios must be queued in the device-mapper core rather
* than here in the target.
*
* m->lock must be held on entry.
*
* If m->queue_if_no_path and m->saved_queue_if_no_path hold the
* same value then we are not between multipath_presuspend()
* and multipath_resume() calls and we have no need to check
* for the DMF_NOFLUSH_SUSPENDING flag.
*/
static int __must_push_back(struct multipath *m)
{
return (m->queue_if_no_path != m->saved_queue_if_no_path &&
dm_noflush_suspending(m->ti));
}
static int map_io(struct multipath *m, struct bio *bio,
struct dm_mpath_io *mpio, unsigned was_queued)
{
int r = DM_MAPIO_REMAPPED;
unsigned long flags;
struct pgpath *pgpath;
spin_lock_irqsave(&m->lock, flags);
/* Do we need to select a new pgpath? */
if (!m->current_pgpath ||
(!m->queue_io && (m->repeat_count && --m->repeat_count == 0)))
__choose_pgpath(m);
pgpath = m->current_pgpath;
if (was_queued)
m->queue_size--;
if ((pgpath && m->queue_io) ||
(!pgpath && m->queue_if_no_path)) {
/* Queue for the daemon to resubmit */
bio_list_add(&m->queued_ios, bio);
m->queue_size++;
if ((m->pg_init_required && !m->pg_init_in_progress) ||
!m->queue_io)
queue_work(kmultipathd, &m->process_queued_ios);
pgpath = NULL;
r = DM_MAPIO_SUBMITTED;
} else if (pgpath)
bio->bi_bdev = pgpath->path.dev->bdev;
else if (__must_push_back(m))
r = DM_MAPIO_REQUEUE;
else
r = -EIO; /* Failed */
mpio->pgpath = pgpath;
spin_unlock_irqrestore(&m->lock, flags);
return r;
}
/*
* If we run out of usable paths, should we queue I/O or error it?
*/
static int queue_if_no_path(struct multipath *m, unsigned queue_if_no_path,
unsigned save_old_value)
{
unsigned long flags;
spin_lock_irqsave(&m->lock, flags);
if (save_old_value)
m->saved_queue_if_no_path = m->queue_if_no_path;
else
m->saved_queue_if_no_path = queue_if_no_path;
m->queue_if_no_path = queue_if_no_path;
if (!m->queue_if_no_path && m->queue_size)
queue_work(kmultipathd, &m->process_queued_ios);
spin_unlock_irqrestore(&m->lock, flags);
return 0;
}
/*-----------------------------------------------------------------
* The multipath daemon is responsible for resubmitting queued ios.
*---------------------------------------------------------------*/
static void dispatch_queued_ios(struct multipath *m)
{
int r;
unsigned long flags;
struct bio *bio = NULL, *next;
struct dm_mpath_io *mpio;
union map_info *info;
spin_lock_irqsave(&m->lock, flags);
bio = bio_list_get(&m->queued_ios);
spin_unlock_irqrestore(&m->lock, flags);
while (bio) {
next = bio->bi_next;
bio->bi_next = NULL;
info = dm_get_mapinfo(bio);
mpio = info->ptr;
r = map_io(m, bio, mpio, 1);
if (r < 0)
bio_endio(bio, r);
else if (r == DM_MAPIO_REMAPPED)
generic_make_request(bio);
else if (r == DM_MAPIO_REQUEUE)
bio_endio(bio, -EIO);
bio = next;
}
}
static void process_queued_ios(struct work_struct *work)
{
struct multipath *m =
container_of(work, struct multipath, process_queued_ios);
struct pgpath *pgpath = NULL;
unsigned init_required = 0, must_queue = 1;
unsigned long flags;
spin_lock_irqsave(&m->lock, flags);
if (!m->queue_size)
goto out;
if (!m->current_pgpath)
__choose_pgpath(m);
pgpath = m->current_pgpath;
if ((pgpath && !m->queue_io) ||
(!pgpath && !m->queue_if_no_path))
must_queue = 0;
if (m->pg_init_required && !m->pg_init_in_progress && pgpath) {
m->pgpath_to_activate = pgpath;
m->pg_init_count++;
m->pg_init_required = 0;
m->pg_init_in_progress = 1;
init_required = 1;
}
out:
spin_unlock_irqrestore(&m->lock, flags);
if (init_required)
queue_work(kmpath_handlerd, &m->activate_path);
if (!must_queue)
dispatch_queued_ios(m);
}
/*
* An event is triggered whenever a path is taken out of use.
* Includes path failure and PG bypass.
*/
static void trigger_event(struct work_struct *work)
{
struct multipath *m =
container_of(work, struct multipath, trigger_event);
dm_table_event(m->ti->table);
}
/*-----------------------------------------------------------------
* Constructor/argument parsing:
* <#multipath feature args> [<arg>]*
* <#hw_handler args> [hw_handler [<arg>]*]
* <#priority groups>
* <initial priority group>
* [<selector> <#selector args> [<arg>]*
* <#paths> <#per-path selector args>
* [<path> [<arg>]* ]+ ]+
*---------------------------------------------------------------*/
struct param {
unsigned min;
unsigned max;
char *error;
};
static int read_param(struct param *param, char *str, unsigned *v, char **error)
{
if (!str ||
(sscanf(str, "%u", v) != 1) ||
(*v < param->min) ||
(*v > param->max)) {
*error = param->error;
return -EINVAL;
}
return 0;
}
struct arg_set {
unsigned argc;
char **argv;
};
static char *shift(struct arg_set *as)
{
char *r;
if (as->argc) {
as->argc--;
r = *as->argv;
as->argv++;
return r;
}
return NULL;
}
static void consume(struct arg_set *as, unsigned n)
{
BUG_ON (as->argc < n);
as->argc -= n;
as->argv += n;
}
static int parse_path_selector(struct arg_set *as, struct priority_group *pg,
struct dm_target *ti)
{
int r;
struct path_selector_type *pst;
unsigned ps_argc;
static struct param _params[] = {
{0, 1024, "invalid number of path selector args"},
};
pst = dm_get_path_selector(shift(as));
if (!pst) {
ti->error = "unknown path selector type";
return -EINVAL;
}
r = read_param(_params, shift(as), &ps_argc, &ti->error);
if (r) {
dm_put_path_selector(pst);
return -EINVAL;
}
r = pst->create(&pg->ps, ps_argc, as->argv);
if (r) {
dm_put_path_selector(pst);
ti->error = "path selector constructor failed";
return r;
}
pg->ps.type = pst;
consume(as, ps_argc);
return 0;
}
static struct pgpath *parse_path(struct arg_set *as, struct path_selector *ps,
struct dm_target *ti)
{
int r;
struct pgpath *p;
struct multipath *m = ti->private;
/* we need at least a path arg */
if (as->argc < 1) {
ti->error = "no device given";
return ERR_PTR(-EINVAL);
}
p = alloc_pgpath();
if (!p)
return ERR_PTR(-ENOMEM);
r = dm_get_device(ti, shift(as), ti->begin, ti->len,
dm_table_get_mode(ti->table), &p->path.dev);
if (r) {
ti->error = "error getting device";
goto bad;
}
if (m->hw_handler_name) {
r = scsi_dh_attach(bdev_get_queue(p->path.dev->bdev),
m->hw_handler_name);
if (r < 0) {
dm_put_device(ti, p->path.dev);
goto bad;
}
}
r = ps->type->add_path(ps, &p->path, as->argc, as->argv, &ti->error);
if (r) {
dm_put_device(ti, p->path.dev);
goto bad;
}
return p;
bad:
free_pgpath(p);
return ERR_PTR(r);
}
static struct priority_group *parse_priority_group(struct arg_set *as,
struct multipath *m)
{
static struct param _params[] = {
{1, 1024, "invalid number of paths"},
{0, 1024, "invalid number of selector args"}
};
int r;
unsigned i, nr_selector_args, nr_params;
struct priority_group *pg;
struct dm_target *ti = m->ti;
if (as->argc < 2) {
as->argc = 0;
ti->error = "not enough priority group arguments";
return ERR_PTR(-EINVAL);
}
pg = alloc_priority_group();
if (!pg) {
ti->error = "couldn't allocate priority group";
return ERR_PTR(-ENOMEM);
}
pg->m = m;
r = parse_path_selector(as, pg, ti);
if (r)
goto bad;
/*
* read the paths
*/
r = read_param(_params, shift(as), &pg->nr_pgpaths, &ti->error);
if (r)
goto bad;
r = read_param(_params + 1, shift(as), &nr_selector_args, &ti->error);
if (r)
goto bad;
nr_params = 1 + nr_selector_args;
for (i = 0; i < pg->nr_pgpaths; i++) {
struct pgpath *pgpath;
struct arg_set path_args;
if (as->argc < nr_params) {
ti->error = "not enough path parameters";
goto bad;
}
path_args.argc = nr_params;
path_args.argv = as->argv;
pgpath = parse_path(&path_args, &pg->ps, ti);
if (IS_ERR(pgpath)) {
r = PTR_ERR(pgpath);
goto bad;
}
pgpath->pg = pg;
list_add_tail(&pgpath->list, &pg->pgpaths);
consume(as, nr_params);
}
return pg;
bad:
free_priority_group(pg, ti);
return ERR_PTR(r);
}
static int parse_hw_handler(struct arg_set *as, struct multipath *m)
{
unsigned hw_argc;
struct dm_target *ti = m->ti;
static struct param _params[] = {
{0, 1024, "invalid number of hardware handler args"},
};
if (read_param(_params, shift(as), &hw_argc, &ti->error))
return -EINVAL;
if (!hw_argc)
return 0;
m->hw_handler_name = kstrdup(shift(as), GFP_KERNEL);
request_module("scsi_dh_%s", m->hw_handler_name);
if (scsi_dh_handler_exist(m->hw_handler_name) == 0) {
ti->error = "unknown hardware handler type";
kfree(m->hw_handler_name);
m->hw_handler_name = NULL;
return -EINVAL;
}
if (hw_argc > 1)
DMWARN("Ignoring user-specified arguments for "
"hardware handler \"%s\"", m->hw_handler_name);
consume(as, hw_argc - 1);
return 0;
}
static int parse_features(struct arg_set *as, struct multipath *m)
{
int r;
unsigned argc;
struct dm_target *ti = m->ti;
const char *param_name;
static struct param _params[] = {
{0, 3, "invalid number of feature args"},
{1, 50, "pg_init_retries must be between 1 and 50"},
};
r = read_param(_params, shift(as), &argc, &ti->error);
if (r)
return -EINVAL;
if (!argc)
return 0;
do {
param_name = shift(as);
argc--;
if (!strnicmp(param_name, MESG_STR("queue_if_no_path"))) {
r = queue_if_no_path(m, 1, 0);
continue;
}
if (!strnicmp(param_name, MESG_STR("pg_init_retries")) &&
(argc >= 1)) {
r = read_param(_params + 1, shift(as),
&m->pg_init_retries, &ti->error);
argc--;
continue;
}
ti->error = "Unrecognised multipath feature request";
r = -EINVAL;
} while (argc && !r);
return r;
}
static int multipath_ctr(struct dm_target *ti, unsigned int argc,
char **argv)
{
/* target parameters */
static struct param _params[] = {
{1, 1024, "invalid number of priority groups"},
{1, 1024, "invalid initial priority group number"},
};
int r;
struct multipath *m;
struct arg_set as;
unsigned pg_count = 0;
unsigned next_pg_num;
as.argc = argc;
as.argv = argv;
m = alloc_multipath(ti);
if (!m) {
ti->error = "can't allocate multipath";
return -EINVAL;
}
r = parse_features(&as, m);
if (r)
goto bad;
r = parse_hw_handler(&as, m);
if (r)
goto bad;
r = read_param(_params, shift(&as), &m->nr_priority_groups, &ti->error);
if (r)
goto bad;
r = read_param(_params + 1, shift(&as), &next_pg_num, &ti->error);
if (r)
goto bad;
/* parse the priority groups */
while (as.argc) {
struct priority_group *pg;
pg = parse_priority_group(&as, m);
if (IS_ERR(pg)) {
r = PTR_ERR(pg);
goto bad;
}
m->nr_valid_paths += pg->nr_pgpaths;
list_add_tail(&pg->list, &m->priority_groups);
pg_count++;
pg->pg_num = pg_count;
if (!--next_pg_num)
m->next_pg = pg;
}
if (pg_count != m->nr_priority_groups) {
ti->error = "priority group count mismatch";
r = -EINVAL;
goto bad;
}
return 0;
bad:
free_multipath(m);
return r;
}
static void multipath_dtr(struct dm_target *ti)
{
struct multipath *m = (struct multipath *) ti->private;
flush_workqueue(kmpath_handlerd);
flush_workqueue(kmultipathd);
free_multipath(m);
}
/*
* Map bios, recording original fields for later in case we have to resubmit
*/
static int multipath_map(struct dm_target *ti, struct bio *bio,
union map_info *map_context)
{
int r;
struct dm_mpath_io *mpio;
struct multipath *m = (struct multipath *) ti->private;
mpio = mempool_alloc(m->mpio_pool, GFP_NOIO);
dm_bio_record(&mpio->details, bio);
map_context->ptr = mpio;
bio->bi_rw |= (1 << BIO_RW_FAILFAST_TRANSPORT);
r = map_io(m, bio, mpio, 0);
if (r < 0 || r == DM_MAPIO_REQUEUE)
mempool_free(mpio, m->mpio_pool);
return r;
}
/*
* Take a path out of use.
*/
static int fail_path(struct pgpath *pgpath)
{
unsigned long flags;
struct multipath *m = pgpath->pg->m;
spin_lock_irqsave(&m->lock, flags);
if (!pgpath->is_active)
goto out;
DMWARN("Failing path %s.", pgpath->path.dev->name);
pgpath->pg->ps.type->fail_path(&pgpath->pg->ps, &pgpath->path);
pgpath->is_active = 0;
pgpath->fail_count++;
m->nr_valid_paths--;
if (pgpath == m->current_pgpath)
m->current_pgpath = NULL;
dm_path_uevent(DM_UEVENT_PATH_FAILED, m->ti,
pgpath->path.dev->name, m->nr_valid_paths);
schedule_work(&m->trigger_event);
queue_work(kmultipathd, &pgpath->deactivate_path);
out:
spin_unlock_irqrestore(&m->lock, flags);
return 0;
}
/*
* Reinstate a previously-failed path
*/
static int reinstate_path(struct pgpath *pgpath)
{
int r = 0;
unsigned long flags;
struct multipath *m = pgpath->pg->m;
spin_lock_irqsave(&m->lock, flags);
if (pgpath->is_active)
goto out;
if (!pgpath->pg->ps.type->reinstate_path) {
DMWARN("Reinstate path not supported by path selector %s",
pgpath->pg->ps.type->name);
r = -EINVAL;
goto out;
}
r = pgpath->pg->ps.type->reinstate_path(&pgpath->pg->ps, &pgpath->path);
if (r)
goto out;
pgpath->is_active = 1;
m->current_pgpath = NULL;
if (!m->nr_valid_paths++ && m->queue_size)
queue_work(kmultipathd, &m->process_queued_ios);
dm_path_uevent(DM_UEVENT_PATH_REINSTATED, m->ti,
pgpath->path.dev->name, m->nr_valid_paths);
schedule_work(&m->trigger_event);
out:
spin_unlock_irqrestore(&m->lock, flags);
return r;
}
/*
* Fail or reinstate all paths that match the provided struct dm_dev.
*/
static int action_dev(struct multipath *m, struct dm_dev *dev,
action_fn action)
{
int r = 0;
struct pgpath *pgpath;
struct priority_group *pg;
list_for_each_entry(pg, &m->priority_groups, list) {
list_for_each_entry(pgpath, &pg->pgpaths, list) {
if (pgpath->path.dev == dev)
r = action(pgpath);
}
}
return r;
}
/*
* Temporarily try to avoid having to use the specified PG
*/
static void bypass_pg(struct multipath *m, struct priority_group *pg,
int bypassed)
{
unsigned long flags;
spin_lock_irqsave(&m->lock, flags);
pg->bypassed = bypassed;
m->current_pgpath = NULL;
m->current_pg = NULL;
spin_unlock_irqrestore(&m->lock, flags);
schedule_work(&m->trigger_event);
}
/*
* Switch to using the specified PG from the next I/O that gets mapped
*/
static int switch_pg_num(struct multipath *m, const char *pgstr)
{
struct priority_group *pg;
unsigned pgnum;
unsigned long flags;
if (!pgstr || (sscanf(pgstr, "%u", &pgnum) != 1) || !pgnum ||
(pgnum > m->nr_priority_groups)) {
DMWARN("invalid PG number supplied to switch_pg_num");
return -EINVAL;
}
spin_lock_irqsave(&m->lock, flags);
list_for_each_entry(pg, &m->priority_groups, list) {
pg->bypassed = 0;
if (--pgnum)