From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Date: Wed, 15 Jul 2015 09:52:04 +0000 (+0300)
Subject: sched/preempt: Fix cond_resched_lock() and cond_resched_softirq()
X-Git-Tag: omap-for-v4.3/fixes-merge-window~22^2~28
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fe32d3cd5e8eb0f82e459763374aa80797023403;p=pandora-kernel.git

sched/preempt: Fix cond_resched_lock() and cond_resched_softirq()

These functions check should_resched() before unlocking spinlock/bh-enable:
preempt_count always non-zero => should_resched() always returns false.
cond_resched_lock() worked iff spin_needbreak is set.

This patch adds argument "preempt_offset" to should_resched().

preempt_count offset constants for that:

  PREEMPT_DISABLE_OFFSET  - offset after preempt_disable()
  PREEMPT_LOCK_OFFSET     - offset after spin_lock()
  SOFTIRQ_DISABLE_OFFSET  - offset after local_bh_distable()
  SOFTIRQ_LOCK_OFFSET     - offset after spin_lock_bh()

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Graf <agraf@suse.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: bdb438065890 ("sched: Extract the basic add/sub preempt_count modifiers")
Link: http://lkml.kernel.org/r/20150715095204.12246.98268.stgit@buzz
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---

diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index dca71714f860..b12f81022a6b 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -90,9 +90,9 @@ static __always_inline bool __preempt_count_dec_and_test(void)
 /*
  * Returns true when we need to resched and can (barring IRQ state).
  */
-static __always_inline bool should_resched(void)
+static __always_inline bool should_resched(int preempt_offset)
 {
-	return unlikely(!raw_cpu_read_4(__preempt_count));
+	return unlikely(raw_cpu_read_4(__preempt_count) == preempt_offset);
 }
 
 #ifdef CONFIG_PREEMPT
diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h
index d0a7a4753db2..0bec580a4885 100644
--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -71,9 +71,10 @@ static __always_inline bool __preempt_count_dec_and_test(void)
 /*
  * Returns true when we need to resched and can (barring IRQ state).
  */
-static __always_inline bool should_resched(void)
+static __always_inline bool should_resched(int preempt_offset)
 {
-	return unlikely(!preempt_count() && tif_need_resched());
+	return unlikely(preempt_count() == preempt_offset &&
+			tif_need_resched());
 }
 
 #ifdef CONFIG_PREEMPT
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