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preempt_schedule_context() does preempt_enable_notrace() at the end and this can call the same function again; exception_exit() is heavy and it is quite possible that need-resched is true again. 1. Change this code to dec preempt_count() and check need_resched() by hand. 2. As Linus suggested, we can use the PREEMPT_ACTIVE bit and avoid the enable/disable dance around __schedule(). But in this case we need to move into sched/core.c. 3. Cosmetic, but x86 forgets to declare this function. This doesn't really matter because it is only called by asm helpers, still it make sense to add the declaration into asm/preempt.h to match preempt_schedule(). Reported-by: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alexander Graf <agraf@suse.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Christoph Lameter <cl@linux.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Peter Anvin <hpa@zytor.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Chuck Ebbert <cebbert.lkml@gmail.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Link: http://lkml.kernel.org/r/20141005202322.GB27962@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
113 lines
3.0 KiB
C
113 lines
3.0 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 raw_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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raw_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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raw_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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raw_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 !(raw_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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raw_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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raw_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(!raw_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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extern asmlinkage void preempt_schedule_context(void);
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# endif
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#endif
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#endif /* __ASM_PREEMPT_H */
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