Commit 093c8812 authored by Yosry Ahmed's avatar Yosry Ahmed Committed by Tejun Heo
Browse files

cgroup: rstat: Cleanup flushing functions and locking 



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: default avatarYosry Ahmed <yosry.ahmed@linux.dev>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 0efc297a

include/linux/cgroup.h

+0 −2
Original line number Diff line number Diff line
@@ -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.

kernel/cgroup/rstat.c

+20 −59
Original line number Diff line number Diff line
@@ -299,17 +299,29 @@ 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)

/**

 * cgroup_rstat_flush - flush stats in @cgrp's subtree

 * @cgrp: target cgroup

 *

 * Collect all per-cpu stats in @cgrp's subtree into the global counters

 * and propagate them upwards.  After this function returns, all cgroups in

 * the subtree have up-to-date ->stat.

 *

 * This also gets all cgroups in the subtree including @cgrp off the

 * ->updated_children lists.

 *

 * This function may block.

 */

__bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp)

{

	int cpu;



	lockdep_assert_held(&cgroup_rstat_lock);



	might_sleep();

	for_each_possible_cpu(cpu) {

		struct cgroup *pos = cgroup_rstat_updated_list(cgrp, cpu);



		/* 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;
@@ -322,62 +334,10 @@ static void cgroup_rstat_flush_locked(struct cgroup *cgrp) 
				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

 *

 * Collect all per-cpu stats in @cgrp's subtree into the global counters

 * and propagate them upwards.  After this function returns, all cgroups in

 * the subtree have up-to-date ->stat.

 *

 * This also gets all cgroups in the subtree including @cgrp off the

 * ->updated_children lists.

 *

 * This function may block.

 */

__bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp)

{

	might_sleep();



	__cgroup_rstat_lock(cgrp, -1);

	cgroup_rstat_flush_locked(cgrp);

	__cgroup_rstat_unlock(cgrp, -1);

	}



/**

 * 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_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);

}



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);

	}