From 9b4f68fbb4eb6be48cd1d6453a76a1f96cc7852c Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 16 May 2016 15:01:11 +0200 Subject: [PATCH] UPSTREAM: sched/preempt: Fix preempt_count manipulations Vikram reported that his ARM64 compiler managed to 'optimize' away the preempt_count manipulations in code like: preempt_enable_no_resched(); put_user(); preempt_disable(); Irrespective of that fact that that is horrible code that should be fixed for many reasons, it does highlight a deficiency in the generic preempt_count manipulators. As it is never right to combine/elide preempt_count manipulations like this. Therefore sprinkle some volatile in the two generic accessors to ensure the compiler is aware of the fact that the preempt_count is observed outside of the regular program-order view and thus cannot be optimized away like this. x86; the only arch not using the generic code is not affected as we do all this in asm in order to use the segment base per-cpu stuff. Change-Id: I13da06ddb17c533b8150f008514a4c74723b1742 Reported-by: Vikram Mulukutla Tested-by: Vikram Mulukutla Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: a787870924db ("sched, arch: Create asm/preempt.h") Link: http://lkml.kernel.org/r/20160516131751.GH3205@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar Signed-off-by: Huang, Tao (cherry picked from commit 2e636d5e66c35dfcbaf617aa8fa963f6847478fe) --- include/asm-generic/preempt.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h index 5d8ffa3e6f8c..c1cde3577551 100644 --- a/include/asm-generic/preempt.h +++ b/include/asm-generic/preempt.h @@ -7,10 +7,10 @@ static __always_inline int preempt_count(void) { - return current_thread_info()->preempt_count; + return READ_ONCE(current_thread_info()->preempt_count); } -static __always_inline int *preempt_count_ptr(void) +static __always_inline volatile int *preempt_count_ptr(void) { return ¤t_thread_info()->preempt_count; } -- 2.34.1