ba1f14fbe7
While hunting a preemption issue with Alexander, Ben noticed that the currently generic PREEMPT_NEED_RESCHED stuff is horribly broken for load-store architectures. We currently rely on the IPI to fold TIF_NEED_RESCHED into PREEMPT_NEED_RESCHED, but when this IPI lands while we already have a load for the preempt-count but before the store, the store will erase the PREEMPT_NEED_RESCHED change. The current preempt-count only works on load-store archs because interrupts are assumed to be completely balanced wrt their preempt_count fiddling; the previous preempt_count load will match the preempt_count state after the interrupt and therefore nothing gets lost. This patch removes the PREEMPT_NEED_RESCHED usage from generic code and pushes it into x86 arch code; the generic code goes back to relying on TIF_NEED_RESCHED. Boot tested on x86_64 and compile tested on ppc64. Reported-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Reported-and-Tested-by: Alexander Graf <agraf@suse.de> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/20131128132641.GP10022@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
111 lines
3 KiB
C
111 lines
3 KiB
C
#ifndef __ASM_PREEMPT_H
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#define __ASM_PREEMPT_H
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#include <asm/rmwcc.h>
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#include <asm/percpu.h>
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#include <linux/thread_info.h>
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DECLARE_PER_CPU(int, __preempt_count);
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/*
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* We use the PREEMPT_NEED_RESCHED bit as an inverted NEED_RESCHED such
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* that a decrement hitting 0 means we can and should reschedule.
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*/
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#define PREEMPT_ENABLED (0 + PREEMPT_NEED_RESCHED)
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/*
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* We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users
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* that think a non-zero value indicates we cannot preempt.
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*/
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static __always_inline int preempt_count(void)
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{
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return __this_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
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}
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static __always_inline void preempt_count_set(int pc)
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{
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__this_cpu_write_4(__preempt_count, pc);
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}
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/*
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* must be macros to avoid header recursion hell
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*/
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#define task_preempt_count(p) \
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(task_thread_info(p)->saved_preempt_count & ~PREEMPT_NEED_RESCHED)
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#define init_task_preempt_count(p) do { \
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task_thread_info(p)->saved_preempt_count = PREEMPT_DISABLED; \
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} while (0)
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#define init_idle_preempt_count(p, cpu) do { \
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task_thread_info(p)->saved_preempt_count = PREEMPT_ENABLED; \
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per_cpu(__preempt_count, (cpu)) = PREEMPT_ENABLED; \
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} while (0)
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/*
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* We fold the NEED_RESCHED bit into the preempt count such that
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* preempt_enable() can decrement and test for needing to reschedule with a
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* single instruction.
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*
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* We invert the actual bit, so that when the decrement hits 0 we know we both
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* need to resched (the bit is cleared) and can resched (no preempt count).
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*/
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static __always_inline void set_preempt_need_resched(void)
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{
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__this_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
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}
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static __always_inline void clear_preempt_need_resched(void)
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{
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__this_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED);
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}
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static __always_inline bool test_preempt_need_resched(void)
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{
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return !(__this_cpu_read_4(__preempt_count) & PREEMPT_NEED_RESCHED);
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}
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/*
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* The various preempt_count add/sub methods
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*/
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static __always_inline void __preempt_count_add(int val)
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{
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__this_cpu_add_4(__preempt_count, val);
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}
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static __always_inline void __preempt_count_sub(int val)
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{
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__this_cpu_add_4(__preempt_count, -val);
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}
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/*
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* Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule
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* a decrement which hits zero means we have no preempt_count and should
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* reschedule.
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*/
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static __always_inline bool __preempt_count_dec_and_test(void)
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{
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GEN_UNARY_RMWcc("decl", __preempt_count, __percpu_arg(0), "e");
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}
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/*
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* Returns true when we need to resched and can (barring IRQ state).
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*/
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static __always_inline bool should_resched(void)
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{
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return unlikely(!__this_cpu_read_4(__preempt_count));
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}
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#ifdef CONFIG_PREEMPT
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extern asmlinkage void ___preempt_schedule(void);
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# define __preempt_schedule() asm ("call ___preempt_schedule")
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extern asmlinkage void preempt_schedule(void);
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# ifdef CONFIG_CONTEXT_TRACKING
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extern asmlinkage void ___preempt_schedule_context(void);
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# define __preempt_schedule_context() asm ("call ___preempt_schedule_context")
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# endif
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#endif
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#endif /* __ASM_PREEMPT_H */
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