From f3c11cb27a8b7c71cf48c8990ace6c8a0783f6db Mon Sep 17 00:00:00 2001 From: Greg Kroah-Hartman Date: Wed, 3 Apr 2024 16:36:42 +0200 Subject: [PATCH] Revert "workqueue: RCU protect wq->dfl_pwq and implement accessors for it" This reverts commit bd31fb926dfa02d2ccfb4b79389168b1d16f36b1 which is commit 9f66cff212bb3c1cd25996aaa0dfd0c9e9d8baab upstream. The workqueue patches backported to 6.6.y caused some reported regressions, so revert them for now. Reported-by: Thorsten Leemhuis Cc: Tejun Heo Cc: Marek Szyprowski Cc: Nathan Chancellor Cc: Sasha Levin Cc: Audra Mitchell Link: https://lore.kernel.org/all/ce4c2f67-c298-48a0-87a3-f933d646c73b@leemhuis.info/ Signed-off-by: Greg Kroah-Hartman --- kernel/workqueue.c | 64 +++++++++++++++++----------------------------- 1 file changed, 24 insertions(+), 40 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 80c0a84aa147c..76559b63ee1fc 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -304,7 +304,7 @@ struct workqueue_struct { int saved_max_active; /* WQ: saved max_active */ struct workqueue_attrs *unbound_attrs; /* PW: only for unbound wqs */ - struct pool_workqueue __rcu *dfl_pwq; /* PW: only for unbound wqs */ + struct pool_workqueue *dfl_pwq; /* PW: only for unbound wqs */ #ifdef CONFIG_SYSFS struct wq_device *wq_dev; /* I: for sysfs interface */ @@ -629,23 +629,6 @@ static int worker_pool_assign_id(struct worker_pool *pool) return ret; } -static struct pool_workqueue __rcu ** -unbound_pwq_slot(struct workqueue_struct *wq, int cpu) -{ - if (cpu >= 0) - return per_cpu_ptr(wq->cpu_pwq, cpu); - else - return &wq->dfl_pwq; -} - -/* @cpu < 0 for dfl_pwq */ -static struct pool_workqueue *unbound_pwq(struct workqueue_struct *wq, int cpu) -{ - return rcu_dereference_check(*unbound_pwq_slot(wq, cpu), - lockdep_is_held(&wq_pool_mutex) || - lockdep_is_held(&wq->mutex)); -} - static unsigned int work_color_to_flags(int color) { return color << WORK_STRUCT_COLOR_SHIFT; @@ -4335,11 +4318,10 @@ static void wq_calc_pod_cpumask(struct workqueue_attrs *attrs, int cpu, "possible intersect\n"); } -/* install @pwq into @wq and return the old pwq, @cpu < 0 for dfl_pwq */ +/* install @pwq into @wq's cpu_pwq and return the old pwq */ static struct pool_workqueue *install_unbound_pwq(struct workqueue_struct *wq, int cpu, struct pool_workqueue *pwq) { - struct pool_workqueue __rcu **slot = unbound_pwq_slot(wq, cpu); struct pool_workqueue *old_pwq; lockdep_assert_held(&wq_pool_mutex); @@ -4348,8 +4330,8 @@ static struct pool_workqueue *install_unbound_pwq(struct workqueue_struct *wq, /* link_pwq() can handle duplicate calls */ link_pwq(pwq); - old_pwq = rcu_access_pointer(*slot); - rcu_assign_pointer(*slot, pwq); + old_pwq = rcu_access_pointer(*per_cpu_ptr(wq->cpu_pwq, cpu)); + rcu_assign_pointer(*per_cpu_ptr(wq->cpu_pwq, cpu), pwq); return old_pwq; } @@ -4449,11 +4431,14 @@ static void apply_wqattrs_commit(struct apply_wqattrs_ctx *ctx) copy_workqueue_attrs(ctx->wq->unbound_attrs, ctx->attrs); - /* save the previous pwqs and install the new ones */ + /* save the previous pwq and install the new one */ for_each_possible_cpu(cpu) ctx->pwq_tbl[cpu] = install_unbound_pwq(ctx->wq, cpu, ctx->pwq_tbl[cpu]); - ctx->dfl_pwq = install_unbound_pwq(ctx->wq, -1, ctx->dfl_pwq); + + /* @dfl_pwq might not have been used, ensure it's linked */ + link_pwq(ctx->dfl_pwq); + swap(ctx->wq->dfl_pwq, ctx->dfl_pwq); mutex_unlock(&ctx->wq->mutex); } @@ -4576,7 +4561,9 @@ static void wq_update_pod(struct workqueue_struct *wq, int cpu, /* nothing to do if the target cpumask matches the current pwq */ wq_calc_pod_cpumask(target_attrs, cpu, off_cpu); - if (wqattrs_equal(target_attrs, unbound_pwq(wq, cpu)->pool->attrs)) + pwq = rcu_dereference_protected(*per_cpu_ptr(wq->cpu_pwq, cpu), + lockdep_is_held(&wq_pool_mutex)); + if (wqattrs_equal(target_attrs, pwq->pool->attrs)) return; /* create a new pwq */ @@ -4594,11 +4581,10 @@ static void wq_update_pod(struct workqueue_struct *wq, int cpu, use_dfl_pwq: mutex_lock(&wq->mutex); - pwq = unbound_pwq(wq, -1); - raw_spin_lock_irq(&pwq->pool->lock); - get_pwq(pwq); - raw_spin_unlock_irq(&pwq->pool->lock); - old_pwq = install_unbound_pwq(wq, cpu, pwq); + raw_spin_lock_irq(&wq->dfl_pwq->pool->lock); + get_pwq(wq->dfl_pwq); + raw_spin_unlock_irq(&wq->dfl_pwq->pool->lock); + old_pwq = install_unbound_pwq(wq, cpu, wq->dfl_pwq); out_unlock: mutex_unlock(&wq->mutex); put_pwq_unlocked(old_pwq); @@ -4636,13 +4622,10 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq) cpus_read_lock(); if (wq->flags & __WQ_ORDERED) { - struct pool_workqueue *dfl_pwq; - ret = apply_workqueue_attrs(wq, ordered_wq_attrs[highpri]); /* there should only be single pwq for ordering guarantee */ - dfl_pwq = rcu_access_pointer(wq->dfl_pwq); - WARN(!ret && (wq->pwqs.next != &dfl_pwq->pwqs_node || - wq->pwqs.prev != &dfl_pwq->pwqs_node), + WARN(!ret && (wq->pwqs.next != &wq->dfl_pwq->pwqs_node || + wq->pwqs.prev != &wq->dfl_pwq->pwqs_node), "ordering guarantee broken for workqueue %s\n", wq->name); } else { ret = apply_workqueue_attrs(wq, unbound_std_wq_attrs[highpri]); @@ -4873,7 +4856,7 @@ static bool pwq_busy(struct pool_workqueue *pwq) if (pwq->nr_in_flight[i]) return true; - if ((pwq != rcu_access_pointer(pwq->wq->dfl_pwq)) && (pwq->refcnt > 1)) + if ((pwq != pwq->wq->dfl_pwq) && (pwq->refcnt > 1)) return true; if (!pwq_is_empty(pwq)) return true; @@ -4957,12 +4940,13 @@ void destroy_workqueue(struct workqueue_struct *wq) rcu_read_lock(); for_each_possible_cpu(cpu) { - put_pwq_unlocked(unbound_pwq(wq, cpu)); - RCU_INIT_POINTER(*unbound_pwq_slot(wq, cpu), NULL); + pwq = rcu_access_pointer(*per_cpu_ptr(wq->cpu_pwq, cpu)); + RCU_INIT_POINTER(*per_cpu_ptr(wq->cpu_pwq, cpu), NULL); + put_pwq_unlocked(pwq); } - put_pwq_unlocked(unbound_pwq(wq, -1)); - RCU_INIT_POINTER(*unbound_pwq_slot(wq, -1), NULL); + put_pwq_unlocked(wq->dfl_pwq); + wq->dfl_pwq = NULL; rcu_read_unlock(); }