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Revert "workqueue: Implement system-wide nr_active enforcement for unbound workqueues"

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This reverts commit 5a70baec2294e8a7d0fcc4558741c23e752dad5c which is
commit 5797b1c18919cd9c289ded7954383e499f729ce0 upstream.

The workqueue patches backported to 6.6.y caused some reported
regressions, so revert them for now.

Reported-by: Thorsten Leemhuis <regressions@leemhuis.info>
Cc: Tejun Heo <tj@kernel.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Audra Mitchell <audra@redhat.com>
Link: https://lore.kernel.org/all/ce4c2f67-c298-48a0-87a3-f933d646c73b@leemhuis.info/
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Greg Kroah-Hartman 2024-04-03 16:36:17 +02:00
parent a75ac2693d
commit 6741dd3fd3
2 changed files with 35 additions and 341 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
include/linux/workqueue.h
View File

@ -405,13 +405,6 @@ enum {
WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
WQ_UNBOUND_MAX_ACTIVE = WQ_MAX_ACTIVE,
WQ_DFL_ACTIVE = WQ_MAX_ACTIVE / 2,
/*
* Per-node default cap on min_active. Unless explicitly set, min_active
* is set to min(max_active, WQ_DFL_MIN_ACTIVE). For more details, see
* workqueue_struct->min_active definition.
*/
WQ_DFL_MIN_ACTIVE = 8,
};
/*
@ -454,33 +447,11 @@ extern struct workqueue_struct *system_freezable_power_efficient_wq;
* alloc_workqueue - allocate a workqueue
* @fmt: printf format for the name of the workqueue
* @flags: WQ_* flags
* @max_active: max in-flight work items, 0 for default
* @max_active: max in-flight work items per CPU, 0 for default
* remaining args: args for @fmt
*
* For a per-cpu workqueue, @max_active limits the number of in-flight work
* items for each CPU. e.g. @max_active of 1 indicates that each CPU can be
* executing at most one work item for the workqueue.
*
* For unbound workqueues, @max_active limits the number of in-flight work items
* for the whole system. e.g. @max_active of 16 indicates that that there can be
* at most 16 work items executing for the workqueue in the whole system.
*
* As sharing the same active counter for an unbound workqueue across multiple
* NUMA nodes can be expensive, @max_active is distributed to each NUMA node
* according to the proportion of the number of online CPUs and enforced
* independently.
*
* Depending on online CPU distribution, a node may end up with per-node
* max_active which is significantly lower than @max_active, which can lead to
* deadlocks if the per-node concurrency limit is lower than the maximum number
* of interdependent work items for the workqueue.
*
* To guarantee forward progress regardless of online CPU distribution, the
* concurrency limit on every node is guaranteed to be equal to or greater than
* min_active which is set to min(@max_active, %WQ_DFL_MIN_ACTIVE). This means
* that the sum of per-node max_active's may be larger than @max_active.
*
* For detailed information on %WQ_* flags, please refer to
* Allocate a workqueue with the specified parameters. For detailed
* information on WQ_* flags, please refer to
* Documentation/core-api/workqueue.rst.
*
* RETURNS:

341
kernel/workqueue.c
View File

@ -122,9 +122,6 @@ enum {
*
* L: pool->lock protected. Access with pool->lock held.
*
* LN: pool->lock and wq_node_nr_active->lock protected for writes. Either for
* reads.
*
* K: Only modified by worker while holding pool->lock. Can be safely read by
* self, while holding pool->lock or from IRQ context if %current is the
* kworker.
@ -246,18 +243,17 @@ struct pool_workqueue {
* pwq->inactive_works instead of pool->worklist and marked with
* WORK_STRUCT_INACTIVE.
*
* All work items marked with WORK_STRUCT_INACTIVE do not participate in
* nr_active and all work items in pwq->inactive_works are marked with
* WORK_STRUCT_INACTIVE. But not all WORK_STRUCT_INACTIVE work items are
* in pwq->inactive_works. Some of them are ready to run in
* pool->worklist or worker->scheduled. Those work itmes are only struct
* wq_barrier which is used for flush_work() and should not participate
* in nr_active. For non-barrier work item, it is marked with
* WORK_STRUCT_INACTIVE iff it is in pwq->inactive_works.
* All work items marked with WORK_STRUCT_INACTIVE do not participate
* in pwq->nr_active and all work items in pwq->inactive_works are
* marked with WORK_STRUCT_INACTIVE. But not all WORK_STRUCT_INACTIVE
* work items are in pwq->inactive_works. Some of them are ready to
* run in pool->worklist or worker->scheduled. Those work itmes are
* only struct wq_barrier which is used for flush_work() and should
* not participate in pwq->nr_active. For non-barrier work item, it
* is marked with WORK_STRUCT_INACTIVE iff it is in pwq->inactive_works.
*/
int nr_active; /* L: nr of active works */
struct list_head inactive_works; /* L: inactive works */
struct list_head pending_node; /* LN: node on wq_node_nr_active->pending_pwqs */
struct list_head pwqs_node; /* WR: node on wq->pwqs */
struct list_head mayday_node; /* MD: node on wq->maydays */
@ -289,19 +285,9 @@ struct wq_device;
* on each CPU, in an unbound workqueue, max_active applies to the whole system.
* As sharing a single nr_active across multiple sockets can be very expensive,
* the counting and enforcement is per NUMA node.
*
* The following struct is used to enforce per-node max_active. When a pwq wants
* to start executing a work item, it should increment ->nr using
* tryinc_node_nr_active(). If acquisition fails due to ->nr already being over
* ->max, the pwq is queued on ->pending_pwqs. As in-flight work items finish
* and decrement ->nr, node_activate_pending_pwq() activates the pending pwqs in
* round-robin order.
*/
struct wq_node_nr_active {
int max; /* per-node max_active */
atomic_t nr; /* per-node nr_active */
raw_spinlock_t lock; /* nests inside pool locks */
struct list_head pending_pwqs; /* LN: pwqs with inactive works */
atomic_t nr; /* per-node nr_active count */
};
/*
@ -324,12 +310,8 @@ struct workqueue_struct {
struct worker *rescuer; /* MD: rescue worker */
int nr_drainers; /* WQ: drain in progress */
/* See alloc_workqueue() function comment for info on min/max_active */
int max_active; /* WO: max active works */
int min_active; /* WO: min active works */
int saved_max_active; /* WQ: saved max_active */
int saved_min_active; /* WQ: saved min_active */
struct workqueue_attrs *unbound_attrs; /* PW: only for unbound wqs */
struct pool_workqueue __rcu *dfl_pwq; /* PW: only for unbound wqs */
@ -675,19 +657,6 @@ static struct pool_workqueue *unbound_pwq(struct workqueue_struct *wq, int cpu)
lockdep_is_held(&wq->mutex));
}
/**
* unbound_effective_cpumask - effective cpumask of an unbound workqueue
* @wq: workqueue of interest
*
* @wq->unbound_attrs->cpumask contains the cpumask requested by the user which
* is masked with wq_unbound_cpumask to determine the effective cpumask. The
* default pwq is always mapped to the pool with the current effective cpumask.
*/
static struct cpumask *unbound_effective_cpumask(struct workqueue_struct *wq)
{
return unbound_pwq(wq, -1)->pool->attrs->__pod_cpumask;
}
static unsigned int work_color_to_flags(int color)
{
return color << WORK_STRUCT_COLOR_SHIFT;
@ -1482,46 +1451,6 @@ static struct wq_node_nr_active *wq_node_nr_active(struct workqueue_struct *wq,
return wq->node_nr_active[node];
}
/**
* wq_update_node_max_active - Update per-node max_actives to use
* @wq: workqueue to update
* @off_cpu: CPU that's going down, -1 if a CPU is not going down
*
* Update @wq->node_nr_active[]->max. @wq must be unbound. max_active is
* distributed among nodes according to the proportions of numbers of online
* cpus. The result is always between @wq->min_active and max_active.
*/
static void wq_update_node_max_active(struct workqueue_struct *wq, int off_cpu)
{
struct cpumask *effective = unbound_effective_cpumask(wq);
int min_active = READ_ONCE(wq->min_active);
int max_active = READ_ONCE(wq->max_active);
int total_cpus, node;
lockdep_assert_held(&wq->mutex);
if (!cpumask_test_cpu(off_cpu, effective))
off_cpu = -1;
total_cpus = cpumask_weight_and(effective, cpu_online_mask);
if (off_cpu >= 0)
total_cpus--;
for_each_node(node) {
int node_cpus;
node_cpus = cpumask_weight_and(effective, cpumask_of_node(node));
if (off_cpu >= 0 && cpu_to_node(off_cpu) == node)
node_cpus--;
wq_node_nr_active(wq, node)->max =
clamp(DIV_ROUND_UP(max_active * node_cpus, total_cpus),
min_active, max_active);
}
wq_node_nr_active(wq, NUMA_NO_NODE)->max = min_active;
}
/**
* get_pwq - get an extra reference on the specified pool_workqueue
* @pwq: pool_workqueue to get
@ -1619,98 +1548,35 @@ static bool pwq_activate_work(struct pool_workqueue *pwq,
return true;
}
static bool tryinc_node_nr_active(struct wq_node_nr_active *nna)
{
int max = READ_ONCE(nna->max);
while (true) {
int old, tmp;
old = atomic_read(&nna->nr);
if (old >= max)
return false;
tmp = atomic_cmpxchg_relaxed(&nna->nr, old, old + 1);
if (tmp == old)
return true;
}
}
/**
* pwq_tryinc_nr_active - Try to increment nr_active for a pwq
* @pwq: pool_workqueue of interest
* @fill: max_active may have increased, try to increase concurrency level
*
* Try to increment nr_active for @pwq. Returns %true if an nr_active count is
* successfully obtained. %false otherwise.
*/
static bool pwq_tryinc_nr_active(struct pool_workqueue *pwq, bool fill)
static bool pwq_tryinc_nr_active(struct pool_workqueue *pwq)
{
struct workqueue_struct *wq = pwq->wq;
struct worker_pool *pool = pwq->pool;
struct wq_node_nr_active *nna = wq_node_nr_active(wq, pool->node);
bool obtained = false;
bool obtained;
lockdep_assert_held(&pool->lock);
if (!nna) {
/* per-cpu workqueue, pwq->nr_active is sufficient */
obtained = pwq->nr_active < READ_ONCE(wq->max_active);
goto out;
}
obtained = pwq->nr_active < READ_ONCE(wq->max_active);
/*
* Unbound workqueue uses per-node shared nr_active $nna. If @pwq is
* already waiting on $nna, pwq_dec_nr_active() will maintain the
* concurrency level. Don't jump the line.
*
* We need to ignore the pending test after max_active has increased as
* pwq_dec_nr_active() can only maintain the concurrency level but not
* increase it. This is indicated by @fill.
*/
if (!list_empty(&pwq->pending_node) && likely(!fill))
goto out;
obtained = tryinc_node_nr_active(nna);
if (obtained)
goto out;
/*
* Lockless acquisition failed. Lock, add ourself to $nna->pending_pwqs
* and try again. The smp_mb() is paired with the implied memory barrier
* of atomic_dec_return() in pwq_dec_nr_active() to ensure that either
* we see the decremented $nna->nr or they see non-empty
* $nna->pending_pwqs.
*/
raw_spin_lock(&nna->lock);
if (list_empty(&pwq->pending_node))
list_add_tail(&pwq->pending_node, &nna->pending_pwqs);
else if (likely(!fill))
goto out_unlock;
smp_mb();
obtained = tryinc_node_nr_active(nna);
/*
* If @fill, @pwq might have already been pending. Being spuriously
* pending in cold paths doesn't affect anything. Let's leave it be.
*/
if (obtained && likely(!fill))
list_del_init(&pwq->pending_node);
out_unlock:
raw_spin_unlock(&nna->lock);
out:
if (obtained)
if (obtained) {
pwq->nr_active++;
if (nna)
atomic_inc(&nna->nr);
}
return obtained;
}
/**
* pwq_activate_first_inactive - Activate the first inactive work item on a pwq
* @pwq: pool_workqueue of interest
* @fill: max_active may have increased, try to increase concurrency level
*
* Activate the first inactive work item of @pwq if available and allowed by
* max_active limit.
@ -1718,13 +1584,13 @@ out:
* Returns %true if an inactive work item has been activated. %false if no
* inactive work item is found or max_active limit is reached.
*/
static bool pwq_activate_first_inactive(struct pool_workqueue *pwq, bool fill)
static bool pwq_activate_first_inactive(struct pool_workqueue *pwq)
{
struct work_struct *work =
list_first_entry_or_null(&pwq->inactive_works,
struct work_struct, entry);
if (work && pwq_tryinc_nr_active(pwq, fill)) {
if (work && pwq_tryinc_nr_active(pwq)) {
__pwq_activate_work(pwq, work);
return true;
} else {
@ -1732,93 +1598,11 @@ static bool pwq_activate_first_inactive(struct pool_workqueue *pwq, bool fill)
}
}
/**
* node_activate_pending_pwq - Activate a pending pwq on a wq_node_nr_active
* @nna: wq_node_nr_active to activate a pending pwq for
* @caller_pool: worker_pool the caller is locking
*
* Activate a pwq in @nna->pending_pwqs. Called with @caller_pool locked.
* @caller_pool may be unlocked and relocked to lock other worker_pools.
*/
static void node_activate_pending_pwq(struct wq_node_nr_active *nna,
struct worker_pool *caller_pool)
{
struct worker_pool *locked_pool = caller_pool;
struct pool_workqueue *pwq;
struct work_struct *work;
lockdep_assert_held(&caller_pool->lock);
raw_spin_lock(&nna->lock);
retry:
pwq = list_first_entry_or_null(&nna->pending_pwqs,
struct pool_workqueue, pending_node);
if (!pwq)
goto out_unlock;
/*
* If @pwq is for a different pool than @locked_pool, we need to lock
* @pwq->pool->lock. Let's trylock first. If unsuccessful, do the unlock
* / lock dance. For that, we also need to release @nna->lock as it's
* nested inside pool locks.
*/
if (pwq->pool != locked_pool) {
raw_spin_unlock(&locked_pool->lock);
locked_pool = pwq->pool;
if (!raw_spin_trylock(&locked_pool->lock)) {
raw_spin_unlock(&nna->lock);
raw_spin_lock(&locked_pool->lock);
raw_spin_lock(&nna->lock);
goto retry;
}
}
/*
* $pwq may not have any inactive work items due to e.g. cancellations.
* Drop it from pending_pwqs and see if there's another one.
*/
work = list_first_entry_or_null(&pwq->inactive_works,
struct work_struct, entry);
if (!work) {
list_del_init(&pwq->pending_node);
goto retry;
}
/*
* Acquire an nr_active count and activate the inactive work item. If
* $pwq still has inactive work items, rotate it to the end of the
* pending_pwqs so that we round-robin through them. This means that
* inactive work items are not activated in queueing order which is fine
* given that there has never been any ordering across different pwqs.
*/
if (likely(tryinc_node_nr_active(nna))) {
pwq->nr_active++;
__pwq_activate_work(pwq, work);
if (list_empty(&pwq->inactive_works))
list_del_init(&pwq->pending_node);
else
list_move_tail(&pwq->pending_node, &nna->pending_pwqs);
/* if activating a foreign pool, make sure it's running */
if (pwq->pool != caller_pool)
kick_pool(pwq->pool);
}
out_unlock:
raw_spin_unlock(&nna->lock);
if (locked_pool != caller_pool) {
raw_spin_unlock(&locked_pool->lock);
raw_spin_lock(&caller_pool->lock);
}
}
/**
* pwq_dec_nr_active - Retire an active count
* @pwq: pool_workqueue of interest
*
* Decrement @pwq's nr_active and try to activate the first inactive work item.
* For unbound workqueues, this function may temporarily drop @pwq->pool->lock.
*/
static void pwq_dec_nr_active(struct pool_workqueue *pwq)
{
@ -1838,29 +1622,12 @@ static void pwq_dec_nr_active(struct pool_workqueue *pwq)
* inactive work item on @pwq itself.
*/
if (!nna) {
pwq_activate_first_inactive(pwq, false);
pwq_activate_first_inactive(pwq);
return;
}
/*
* If @pwq is for an unbound workqueue, it's more complicated because
* multiple pwqs and pools may be sharing the nr_active count. When a
* pwq needs to wait for an nr_active count, it puts itself on
* $nna->pending_pwqs. The following atomic_dec_return()'s implied
* memory barrier is paired with smp_mb() in pwq_tryinc_nr_active() to
* guarantee that either we see non-empty pending_pwqs or they see
* decremented $nna->nr.
*
* $nna->max may change as CPUs come online/offline and @pwq->wq's
* max_active gets updated. However, it is guaranteed to be equal to or
* larger than @pwq->wq->min_active which is above zero unless freezing.
* This maintains the forward progress guarantee.
*/
if (atomic_dec_return(&nna->nr) >= READ_ONCE(nna->max))
return;
if (!list_empty(&nna->pending_pwqs))
node_activate_pending_pwq(nna, pool);
atomic_dec(&nna->nr);
pwq_activate_first_inactive(pwq);
}
/**
@ -2181,7 +1948,7 @@ retry:
* @work must also queue behind existing inactive work items to maintain
* ordering when max_active changes. See wq_adjust_max_active().
*/
if (list_empty(&pwq->inactive_works) && pwq_tryinc_nr_active(pwq, false)) {
if (list_empty(&pwq->inactive_works) && pwq_tryinc_nr_active(pwq)) {
if (list_empty(&pool->worklist))
pool->watchdog_ts = jiffies;
@ -3414,7 +3181,7 @@ static void insert_wq_barrier(struct pool_workqueue *pwq,
barr->task = current;
/* The barrier work item does not participate in nr_active. */
/* The barrier work item does not participate in pwq->nr_active. */
work_flags |= WORK_STRUCT_INACTIVE;
/*
@ -4330,8 +4097,6 @@ static void free_node_nr_active(struct wq_node_nr_active **nna_ar)
static void init_node_nr_active(struct wq_node_nr_active *nna)
{
atomic_set(&nna->nr, 0);
raw_spin_lock_init(&nna->lock);
INIT_LIST_HEAD(&nna->pending_pwqs);
}
/*
@ -4571,15 +4336,6 @@ static void pwq_release_workfn(struct kthread_work *work)
mutex_unlock(&wq_pool_mutex);
}
if (!list_empty(&pwq->pending_node)) {
struct wq_node_nr_active *nna =
wq_node_nr_active(pwq->wq, pwq->pool->node);
raw_spin_lock_irq(&nna->lock);
list_del_init(&pwq->pending_node);
raw_spin_unlock_irq(&nna->lock);
}
call_rcu(&pwq->rcu, rcu_free_pwq);
/*
@ -4605,7 +4361,6 @@ static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq,
pwq->flush_color = -1;
pwq->refcnt = 1;
INIT_LIST_HEAD(&pwq->inactive_works);
INIT_LIST_HEAD(&pwq->pending_node);
INIT_LIST_HEAD(&pwq->pwqs_node);
INIT_LIST_HEAD(&pwq->mayday_node);
kthread_init_work(&pwq->release_work, pwq_release_workfn);
@ -4813,9 +4568,6 @@ static void apply_wqattrs_commit(struct apply_wqattrs_ctx *ctx)
ctx->pwq_tbl[cpu]);
ctx->dfl_pwq = install_unbound_pwq(ctx->wq, -1, ctx->dfl_pwq);
/* update node_nr_active->max */
wq_update_node_max_active(ctx->wq, -1);
mutex_unlock(&ctx->wq->mutex);
}
@ -5089,35 +4841,24 @@ static int init_rescuer(struct workqueue_struct *wq)
static void wq_adjust_max_active(struct workqueue_struct *wq)
{
bool activated;
int new_max, new_min;
lockdep_assert_held(&wq->mutex);
if ((wq->flags & WQ_FREEZABLE) && workqueue_freezing) {
new_max = 0;
new_min = 0;
} else {
new_max = wq->saved_max_active;
new_min = wq->saved_min_active;
WRITE_ONCE(wq->max_active, 0);
return;
}
if (wq->max_active == new_max && wq->min_active == new_min)
if (wq->max_active == wq->saved_max_active)
return;
/*
* Update @wq->max/min_active and then kick inactive work items if more
* Update @wq->max_active and then kick inactive work items if more
* active work items are allowed. This doesn't break work item ordering
* because new work items are always queued behind existing inactive
* work items if there are any.
*/
WRITE_ONCE(wq->max_active, new_max);
WRITE_ONCE(wq->min_active, new_min);
if (wq->flags & WQ_UNBOUND)
wq_update_node_max_active(wq, -1);
if (new_max == 0)
return;
WRITE_ONCE(wq->max_active, wq->saved_max_active);
/*
* Round-robin through pwq's activating the first inactive work item
@ -5132,7 +4873,7 @@ static void wq_adjust_max_active(struct workqueue_struct *wq)
/* can be called during early boot w/ irq disabled */
raw_spin_lock_irqsave(&pwq->pool->lock, flags);
if (pwq_activate_first_inactive(pwq, true)) {
if (pwq_activate_first_inactive(pwq)) {
activated = true;
kick_pool(pwq->pool);
}
@ -5194,9 +4935,7 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
/* init wq */
wq->flags = flags;
wq->max_active = max_active;
wq->min_active = min(max_active, WQ_DFL_MIN_ACTIVE);
wq->saved_max_active = wq->max_active;
wq->saved_min_active = wq->min_active;
wq->saved_max_active = max_active;
mutex_init(&wq->mutex);
atomic_set(&wq->nr_pwqs_to_flush, 0);
INIT_LIST_HEAD(&wq->pwqs);
@ -5362,8 +5101,7 @@ EXPORT_SYMBOL_GPL(destroy_workqueue);
* @wq: target workqueue
* @max_active: new max_active value.
*
* Set max_active of @wq to @max_active. See the alloc_workqueue() function
* comment.
* Set max_active of @wq to @max_active.
*
* CONTEXT:
* Don't call from IRQ context.
@ -5380,9 +5118,6 @@ void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
wq->flags &= ~__WQ_ORDERED;
wq->saved_max_active = max_active;
if (wq->flags & WQ_UNBOUND)
wq->saved_min_active = min(wq->saved_min_active, max_active);
wq_adjust_max_active(wq);
mutex_unlock(&wq->mutex);
@ -6064,10 +5799,6 @@ int workqueue_online_cpu(unsigned int cpu)
for_each_cpu(tcpu, pt->pod_cpus[pt->cpu_pod[cpu]])
wq_update_pod(wq, tcpu, cpu, true);
mutex_lock(&wq->mutex);
wq_update_node_max_active(wq, -1);
mutex_unlock(&wq->mutex);
}
}
@ -6096,10 +5827,6 @@ int workqueue_offline_cpu(unsigned int cpu)
for_each_cpu(tcpu, pt->pod_cpus[pt->cpu_pod[cpu]])
wq_update_pod(wq, tcpu, cpu, false);
mutex_lock(&wq->mutex);
wq_update_node_max_active(wq, cpu);
mutex_unlock(&wq->mutex);
}
}
mutex_unlock(&wq_pool_mutex);
@ -7296,12 +7023,8 @@ void __init workqueue_init_topology(void)
* combinations to apply per-pod sharing.
*/
list_for_each_entry(wq, &workqueues, list) {
for_each_online_cpu(cpu)
for_each_online_cpu(cpu) {
wq_update_pod(wq, cpu, cpu, true);
if (wq->flags & WQ_UNBOUND) {
mutex_lock(&wq->mutex);
wq_update_node_max_active(wq, -1);
mutex_unlock(&wq->mutex);
}
}