From 093c8812de2d3436744fd10edab9bf816b94f833 Mon Sep 17 00:00:00 2001 From: Yosry Ahmed Date: Wed, 19 Mar 2025 21:00:13 +0000 Subject: [PATCH] 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: Yosry Ahmed Signed-off-by: Tejun Heo --- include/linux/cgroup.h | 2 -- kernel/cgroup/rstat.c | 79 +++++++++++------------------------------- 2 files changed, 20 insertions(+), 61 deletions(-) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 8e7415c64ed1..28e999f2c642 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -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. diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index 2c1053e83945..7831978a26bb 100644 --- a/kernel/cgroup/rstat.c +++ b/kernel/cgroup/rstat.c @@ -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; @@ -322,64 +334,12 @@ 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) { int cpu; @@ -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); }