printk/sched: Introduce special printk_sched() for those awkward moments

There's a few awkward printk()s inside of scheduler guts that people
prefer to keep but really are rather deadlock prone. Fudge around it
by storing the text in a per-cpu buffer and poll it using the existing
printk_tick() handler.

This will drop output when its more frequent than once a tick, however
only the affinity thing could possible go that fast and for that just
one should suffice to notify the admin he's done something silly..

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-wua3lmkt3dg8nfts66o6brne@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/printk.h b/include/linux/printk.h
index f0e22f7..1f77a41 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -101,6 +101,11 @@ asmlinkage __printf(1, 2) __cold
 int printk(const char *fmt, ...);
 
 /*
+ * Special printk facility for scheduler use only, _DO_NOT_USE_ !
+ */
+__printf(1, 2) __cold int printk_sched(const char *fmt, ...);
+
+/*
  * Please don't use printk_ratelimit(), because it shares ratelimiting state
  * with all other unrelated printk_ratelimit() callsites.  Instead use
  * printk_ratelimited() or plain old __ratelimit().
@@ -127,6 +132,11 @@ int printk(const char *s, ...)
 {
 	return 0;
 }
+static inline __printf(1, 2) __cold
+int printk_sched(const char *s, ...)
+{
+	return 0;
+}
 static inline int printk_ratelimit(void)
 {
 	return 0;