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cgroup: rstat: Cleanup flushing functions and locking

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Now that the rstat lock is being re-acquired on every CPU iteration in
cgroup_rstat_flush_locked(), having the initially acquire the lock is
unnecessary and unclear.

Inline cgroup_rstat_flush_locked() into cgroup_rstat_flush() and move
the lock/unlock calls to the beginning and ending of the loop body to
make the critical section obvious.

cgroup_rstat_flush_hold/release() do not make much sense with the lock
being dropped and reacquired internally. Since it has no external
callers, remove it and explicitly acquire the lock in
cgroup_base_stat_cputime_show() instead.

This leaves the code with a single flushing function,
cgroup_rstat_flush().

Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Yosry Ahmed 2025-03-19 21:00:13 +00:00 committed by Tejun Heo
parent 0efc297a3c
commit 093c8812de
2 changed files with 23 additions and 64 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

2
include/linux/cgroup.h
View file

@ -690,8 +690,6 @@ static inline void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen)
*/
void cgroup_rstat_updated(struct cgroup *cgrp, int cpu);
void cgroup_rstat_flush(struct cgroup *cgrp);
void cgroup_rstat_flush_hold(struct cgroup *cgrp);
void cgroup_rstat_flush_release(struct cgroup *cgrp);
/*
* Basic resource stats.

85
kernel/cgroup/rstat.c
View file

@ -299,38 +299,6 @@ static inline void __cgroup_rstat_unlock(struct cgroup *cgrp, int cpu_in_loop)
spin_unlock_irq(&cgroup_rstat_lock);
}
/* see cgroup_rstat_flush() */
static void cgroup_rstat_flush_locked(struct cgroup *cgrp)
__releases(&cgroup_rstat_lock) __acquires(&cgroup_rstat_lock)
{
int cpu;
lockdep_assert_held(&cgroup_rstat_lock);
for_each_possible_cpu(cpu) {
struct cgroup *pos = cgroup_rstat_updated_list(cgrp, cpu);
for (; pos; pos = pos->rstat_flush_next) {
struct cgroup_subsys_state *css;
cgroup_base_stat_flush(pos, cpu);
bpf_rstat_flush(pos, cgroup_parent(pos), cpu);
rcu_read_lock();
list_for_each_entry_rcu(css, &pos->rstat_css_list,
rstat_css_node)
css->ss->css_rstat_flush(css, cpu);
rcu_read_unlock();
}
/* play nice and avoid disabling interrupts for a long time */
__cgroup_rstat_unlock(cgrp, cpu);
if (!cond_resched())
cpu_relax();
__cgroup_rstat_lock(cgrp, cpu);
}
}
/**
* cgroup_rstat_flush - flush stats in @cgrp's subtree
* @cgrp: target cgroup
@ -346,38 +314,30 @@ static void cgroup_rstat_flush_locked(struct cgroup *cgrp)
*/
__bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp)
{
int cpu;
might_sleep();
for_each_possible_cpu(cpu) {
struct cgroup *pos = cgroup_rstat_updated_list(cgrp, cpu);
__cgroup_rstat_lock(cgrp, -1);
cgroup_rstat_flush_locked(cgrp);
__cgroup_rstat_unlock(cgrp, -1);
}
/* Reacquire for each CPU to avoid disabling IRQs too long */
__cgroup_rstat_lock(cgrp, cpu);
for (; pos; pos = pos->rstat_flush_next) {
struct cgroup_subsys_state *css;
/**
* cgroup_rstat_flush_hold - flush stats in @cgrp's subtree and hold
* @cgrp: target cgroup
*
* Flush stats in @cgrp's subtree and prevent further flushes. Must be
* paired with cgroup_rstat_flush_release().
*
* This function may block.
*/
void cgroup_rstat_flush_hold(struct cgroup *cgrp)
__acquires(&cgroup_rstat_lock)
{
might_sleep();
__cgroup_rstat_lock(cgrp, -1);
cgroup_rstat_flush_locked(cgrp);
}
cgroup_base_stat_flush(pos, cpu);
bpf_rstat_flush(pos, cgroup_parent(pos), cpu);
/**
* cgroup_rstat_flush_release - release cgroup_rstat_flush_hold()
* @cgrp: cgroup used by tracepoint
*/
void cgroup_rstat_flush_release(struct cgroup *cgrp)
__releases(&cgroup_rstat_lock)
{
__cgroup_rstat_unlock(cgrp, -1);
rcu_read_lock();
list_for_each_entry_rcu(css, &pos->rstat_css_list,
rstat_css_node)
css->ss->css_rstat_flush(css, cpu);
rcu_read_unlock();
}
__cgroup_rstat_unlock(cgrp, cpu);
if (!cond_resched())
cpu_relax();
}
}
int cgroup_rstat_init(struct cgroup *cgrp)
@ -614,11 +574,12 @@ void cgroup_base_stat_cputime_show(struct seq_file *seq)
struct cgroup_base_stat bstat;
if (cgroup_parent(cgrp)) {
cgroup_rstat_flush_hold(cgrp);
cgroup_rstat_flush(cgrp);
__cgroup_rstat_lock(cgrp, -1);
bstat = cgrp->bstat;
cputime_adjust(&cgrp->bstat.cputime, &cgrp->prev_cputime,
&bstat.cputime.utime, &bstat.cputime.stime);
cgroup_rstat_flush_release(cgrp);
__cgroup_rstat_unlock(cgrp, -1);
} else {
root_cgroup_cputime(&bstat);
}