[PATCH] sched/features: Fix !CONFIG_JUMP_LABEL case

[PATCH] sched/features: Fix !CONFIG_JUMP_LABEL case

[Juri Lelli]

Commit 765cc3a4b224e ("sched/core: Optimize sched_feat() for
!CONFIG_SCHED_DEBUG builds") made sched features static for
!CONFIG_SCHED_DEBUG configurations, but overlooked the CONFIG_
SCHED_DEBUG enabled and !HAVE_JUMP_LABEL cases. For the latter, echoing
changes to /sys/kernel/debug/sched_features has the nasty effect of
effectively changing what sched_features reports, but without actually
changing the scheduler behaviour (since different translation units get
different sysctl_sched_features).

Fix CONFIG_SCHED_DEBUG and !HAVE_JUMP_LABEL configurations by properly
restructuring ifdefs.

Fixes: 765cc3a4b224e ("sched/core: Optimize sched_feat() for !CONFIG_SCHED_DEBUG builds")
Co-developed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
---
 kernel/sched/core.c  |  2 +-
 kernel/sched/sched.h | 13 ++++++++++---
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3dc415f58bd7..a7949e3ed7e7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -44,7 +44,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp);
 
 DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
 
-#if defined(CONFIG_SCHED_DEBUG) && defined(CONFIG_JUMP_LABEL)
+#ifdef CONFIG_SCHED_DEBUG
 /*
  * Debugging: various feature bits
  *
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 28709f6b0975..caf9202b0aab 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1629,7 +1629,7 @@ enum {
 
 #undef SCHED_FEAT
 
-#if defined(CONFIG_SCHED_DEBUG) && defined(CONFIG_JUMP_LABEL)
+#ifdef CONFIG_SCHED_DEBUG
 
 /*
  * To support run-time toggling of sched features, all the translation units
@@ -1637,6 +1637,7 @@ enum {
  */
 extern const_debug unsigned int sysctl_sched_features;
 
+#ifdef HAVE_JUMP_LABEL
 #define SCHED_FEAT(name, enabled)					\
 static __always_inline bool static_branch_##name(struct static_key *key) \
 {									\
@@ -1649,7 +1650,13 @@ static __always_inline bool static_branch_##name(struct static_key *key) \
 extern struct static_key sched_feat_keys[__SCHED_FEAT_NR];
 #define sched_feat(x) (static_branch_##x(&sched_feat_keys[__SCHED_FEAT_##x]))
 
-#else /* !(SCHED_DEBUG && CONFIG_JUMP_LABEL) */
+#else /* !HAVE_JUMP_LABEL */
+
+#define sched_feat(x) (sysctl_sched_features & (1UL << __SCHED_FEAT_##x))
+
+#endif /* HAVE_JUMP_LABEL */
+
+#else /* !SCHED_DEBUG */
 
 /*
  * Each translation unit has its own copy of sysctl_sched_features to allow
@@ -1665,7 +1672,7 @@ static const_debug __maybe_unused unsigned int sysctl_sched_features =
 
 #define sched_feat(x) !!(sysctl_sched_features & (1UL << __SCHED_FEAT_##x))
 
-#endif /* SCHED_DEBUG && CONFIG_JUMP_LABEL */
+#endif /* SCHED_DEBUG */
 
 extern struct static_key_false sched_numa_balancing;
 extern struct static_key_false sched_schedstats;
-- 
2.26.2

Re: [PATCH] sched/features: Fix !CONFIG_JUMP_LABEL case

[Valentin Schneider]

Hi,

On 12/10/20 06:39, Juri Lelli wrote:
> Commit 765cc3a4b224e ("sched/core: Optimize sched_feat() for
> !CONFIG_SCHED_DEBUG builds") made sched features static for
> !CONFIG_SCHED_DEBUG configurations, but overlooked the CONFIG_
> SCHED_DEBUG enabled and !HAVE_JUMP_LABEL cases. For the latter, echoing
> changes to /sys/kernel/debug/sched_features has the nasty effect of
> effectively changing what sched_features reports, but without actually
> changing the scheduler behaviour (since different translation units get
> different sysctl_sched_features).
>
> Fix CONFIG_SCHED_DEBUG and !HAVE_JUMP_LABEL configurations by properly
> restructuring ifdefs.
>

That should be CONFIG_JUMP_LABEL, no? The HAVE stuff should've died with

  e9666d10a567 ("jump_label: move 'asm goto' support test to Kconfig")

> Fixes: 765cc3a4b224e ("sched/core: Optimize sched_feat() for !CONFIG_SCHED_DEBUG builds")
> Co-developed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
> Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>

With the aforementioned replacement (changelog AND diff):

Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>