From: Martin Schwidefsky Date: Mon, 7 Nov 2016 13:01:00 +0000 (+0100) Subject: sched/x86: Do not clear PREEMPT_NEED_RESCHED on preempt count reset X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=f285144f81e814f39342dbf5321d6ba939890b1b;p=openwrt%2Fstaging%2Fblogic.git sched/x86: Do not clear PREEMPT_NEED_RESCHED on preempt count reset The per-cpu preempt count of x86 contains two values, the actual preempt count and the inverted PREEMPT_NEED_RESCHED bit. If a corrupted preempt count is detected the preempt_count_set() function is used to reset the preempt count. In case the inverted PREEMPT_NEED_RESCHED bit is zero at the time of the reset, the preemption indication is lost. Use raw_cpu_cmpxchg_4() to reset only the count part and leave the PREEMPT_NEED_RESCHED bit as it is. This improves the kernel's behavior when it runs into preempt count leaks and tries to fix them up. Signed-off-by: Martin Schwidefsky Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1478523660-733-1-git-send-email-schwidefsky@de.ibm.com Signed-off-by: Ingo Molnar --- diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h index 17f218645701..ec1f3c651150 100644 --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -24,7 +24,13 @@ static __always_inline int preempt_count(void) static __always_inline void preempt_count_set(int pc) { - raw_cpu_write_4(__preempt_count, pc); + int old, new; + + do { + old = raw_cpu_read_4(__preempt_count); + new = (old & PREEMPT_NEED_RESCHED) | + (pc & ~PREEMPT_NEED_RESCHED); + } while (raw_cpu_cmpxchg_4(__preempt_count, old, new) != old); } /*