From cbe08a7835d71e2737eaf5befcd38c24441b1e26 Mon Sep 17 00:00:00 2001 From: Vikram Mulukutla Date: Tue, 24 May 2016 15:37:13 -0700 Subject: 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: I781dc34fdf52823fd34f4bb93872f85847076c66 Cc: stable@vger.kernel.org Cc: Thomas Gleixner Fixes: a787870924db ("sched, arch: Create asm/preempt.h") Reported-by: Vikram Mulukutla Tested-by: Vikram Mulukutla Signed-off-by: Peter Zijlstra (Intel) Git-commit: 2e636d5e66c35dfcbaf617aa8fa963f6847478fe Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git Link: https://lkml.org/lkml/2016/5/16/190 [vmulukut@codeaurora.org: merge conflict fixups] Signed-off-by: Vikram Mulukutla --- include/asm-generic/preempt.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'include') 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; } -- cgit v1.2.3