53 lines
1.9 KiB
Diff
53 lines
1.9 KiB
Diff
From: Peter Zijlstra <peterz@infradead.org>
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Date: Mon, 16 May 2016 15:01:11 +0200
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Subject: [PATCH] sched,preempt: Fix preempt_count manipulations
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.6/older/patches-4.6.2-rt5.tar.xz
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Vikram reported that his ARM64 compiler managed to 'optimize' away the
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preempt_count manipulations in code like:
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preempt_enable_no_resched();
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put_user();
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preempt_disable();
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Irrespective of that fact that that is horrible code that should be
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fixed for many reasons, it does highlight a deficiency in the generic
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preempt_count manipulators. As it is never right to combine/elide
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preempt_count manipulations like this.
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Therefore sprinkle some volatile in the two generic accessors to
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ensure the compiler is aware of the fact that the preempt_count is
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observed outside of the regular program-order view and thus cannot be
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optimized away like this.
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x86; the only arch not using the generic code is not affected as we
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do all this in asm in order to use the segment base per-cpu stuff.
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Cc: stable@vger.kernel.org
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Cc: stable-rt@vger.kernel.org
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Cc: Thomas Gleixner <tglx@linutronix.de>
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Fixes: a787870924db ("sched, arch: Create asm/preempt.h")
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Reported-by: Vikram Mulukutla <markivx@codeaurora.org>
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Tested-by: Vikram Mulukutla <markivx@codeaurora.org>
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Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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include/asm-generic/preempt.h | 4 ++--
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1 file changed, 2 insertions(+), 2 deletions(-)
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--- a/include/asm-generic/preempt.h
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+++ b/include/asm-generic/preempt.h
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@@ -7,10 +7,10 @@
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static __always_inline int preempt_count(void)
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{
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- return current_thread_info()->preempt_count;
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+ return READ_ONCE(current_thread_info()->preempt_count);
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}
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-static __always_inline int *preempt_count_ptr(void)
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+static __always_inline volatile int *preempt_count_ptr(void)
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{
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return ¤t_thread_info()->preempt_count;
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}
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