From: Peter Zijlstra Date: Wed, 1 Apr 2026 13:20:21 +0000 (+0200) Subject: sched/debug: Fix avg_vruntime() usage X-Git-Tag: v7.0-rc7~3^2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e08d007f9d813616ce7093600bc4fdb9c9d81d89;p=thirdparty%2Flinux.git sched/debug: Fix avg_vruntime() usage John reported that stress-ng-yield could make his machine unhappy and managed to bisect it to commit b3d99f43c72b ("sched/fair: Fix zero_vruntime tracking"). The commit in question changes avg_vruntime() from a function that is a pure reader, to a function that updates variables. This turns an unlocked sched/debug usage of this function from a minor mistake into a data corruptor. Fixes: af4cf40470c2 ("sched/fair: Add cfs_rq::avg_vruntime") Fixes: b3d99f43c72b ("sched/fair: Fix zero_vruntime tracking") Reported-by: John Stultz Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Vincent Guittot Tested-by: K Prateek Nayak Tested-by: John Stultz Link: https://patch.msgid.link/20260401132355.196370805@infradead.org --- diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c index b24f40f05019..15bf45b6f912 100644 --- a/kernel/sched/debug.c +++ b/kernel/sched/debug.c @@ -902,6 +902,7 @@ static void print_rq(struct seq_file *m, struct rq *rq, int rq_cpu) void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq) { s64 left_vruntime = -1, zero_vruntime, right_vruntime = -1, left_deadline = -1, spread; + u64 avruntime; struct sched_entity *last, *first, *root; struct rq *rq = cpu_rq(cpu); unsigned long flags; @@ -925,6 +926,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq) if (last) right_vruntime = last->vruntime; zero_vruntime = cfs_rq->zero_vruntime; + avruntime = avg_vruntime(cfs_rq); raw_spin_rq_unlock_irqrestore(rq, flags); SEQ_printf(m, " .%-30s: %Ld.%06ld\n", "left_deadline", @@ -934,7 +936,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq) SEQ_printf(m, " .%-30s: %Ld.%06ld\n", "zero_vruntime", SPLIT_NS(zero_vruntime)); SEQ_printf(m, " .%-30s: %Ld.%06ld\n", "avg_vruntime", - SPLIT_NS(avg_vruntime(cfs_rq))); + SPLIT_NS(avruntime)); SEQ_printf(m, " .%-30s: %Ld.%06ld\n", "right_vruntime", SPLIT_NS(right_vruntime)); spread = right_vruntime - left_vruntime;