From: Valentin Schneider valentin.schneider@arm.com
[ Upstream commit 459b09b5a3254008b63382bf41a9b36d0b590f57 ]
Since CPU capacity asymmetry can stem purely from maximum frequency differences (e.g. Pixel 1), a rebuild of the scheduler topology can be issued upon loading cpufreq, see:
arch_topology.c::init_cpu_capacity_callback()
Turns out that if this rebuild happens *before* sched_debug_init() is run (which is a late initcall), we end up messing up the sched_domain debug directory: passing a NULL parent to debugfs_create_dir() ends up creating the directory at the debugfs root, which in this case creates /sys/kernel/debug/domains (instead of /sys/kernel/debug/sched/domains).
This currently doesn't happen on asymmetric systems which use cpufreq-scpi or cpufreq-dt drivers, as those are loaded via deferred_probe_initcall() (it is also a late initcall, but appears to be ordered *after* sched_debug_init()).
Ionela has been working on detecting maximum frequency asymmetry via ACPI, and that actually happens via a *device* initcall, thus before sched_debug_init(), and causes the aforementionned debugfs mayhem.
One option would be to punt sched_debug_init() down to fs_initcall_sync(). Preventing update_sched_domain_debugfs() from running before sched_debug_init() appears to be the safer option.
Fixes: 3b87f136f8fc ("sched,debug: Convert sysctl sched_domains to debugfs") Signed-off-by: Valentin Schneider valentin.schneider@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: http://lore.kernel.org/r/20210514095339.12979-1-ionela.voinescu@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/debug.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c index c5aacbd492a1..f8c94bebd17d 100644 --- a/kernel/sched/debug.c +++ b/kernel/sched/debug.c @@ -388,6 +388,13 @@ void update_sched_domain_debugfs(void) { int cpu, i;
+ /* + * This can unfortunately be invoked before sched_debug_init() creates + * the debug directory. Don't touch sd_sysctl_cpus until then. + */ + if (!debugfs_sched) + return; + if (!cpumask_available(sd_sysctl_cpus)) { if (!alloc_cpumask_var(&sd_sysctl_cpus, GFP_KERNEL)) return;