mirror of
https://github.com/torvalds/linux.git
synced 2024-12-27 05:11:48 +00:00
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>
112 lines
3.0 KiB
C
112 lines
3.0 KiB
C
#ifndef __ASM_PREEMPT_H
|
|
#define __ASM_PREEMPT_H
|
|
|
|
#include <asm/rmwcc.h>
|
|
#include <asm/percpu.h>
|
|
#include <linux/thread_info.h>
|
|
|
|
DECLARE_PER_CPU(int, __preempt_count);
|
|
|
|
/*
|
|
* We use the PREEMPT_NEED_RESCHED bit as an inverted NEED_RESCHED such
|
|
* that a decrement hitting 0 means we can and should reschedule.
|
|
*/
|
|
#define PREEMPT_ENABLED (0 + PREEMPT_NEED_RESCHED)
|
|
|
|
/*
|
|
* We mask the PREEMPT_NEED_RESCHED bit so as not to confuse all current users
|
|
* that think a non-zero value indicates we cannot preempt.
|
|
*/
|
|
static __always_inline int preempt_count(void)
|
|
{
|
|
return __this_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
|
|
}
|
|
|
|
static __always_inline void preempt_count_set(int pc)
|
|
{
|
|
__this_cpu_write_4(__preempt_count, pc);
|
|
}
|
|
|
|
/*
|
|
* must be macros to avoid header recursion hell
|
|
*/
|
|
#define task_preempt_count(p) \
|
|
(task_thread_info(p)->saved_preempt_count & ~PREEMPT_NEED_RESCHED)
|
|
|
|
#define init_task_preempt_count(p) do { \
|
|
task_thread_info(p)->saved_preempt_count = PREEMPT_DISABLED; \
|
|
} while (0)
|
|
|
|
#define init_idle_preempt_count(p, cpu) do { \
|
|
task_thread_info(p)->saved_preempt_count = PREEMPT_ENABLED; \
|
|
per_cpu(__preempt_count, (cpu)) = PREEMPT_ENABLED; \
|
|
} while (0)
|
|
|
|
/*
|
|
* We fold the NEED_RESCHED bit into the preempt count such that
|
|
* preempt_enable() can decrement and test for needing to reschedule with a
|
|
* single instruction.
|
|
*
|
|
* We invert the actual bit, so that when the decrement hits 0 we know we both
|
|
* need to resched (the bit is cleared) and can resched (no preempt count).
|
|
*/
|
|
|
|
static __always_inline void set_preempt_need_resched(void)
|
|
{
|
|
__this_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
|
|
}
|
|
|
|
static __always_inline void clear_preempt_need_resched(void)
|
|
{
|
|
__this_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED);
|
|
}
|
|
|
|
static __always_inline bool test_preempt_need_resched(void)
|
|
{
|
|
return !(__this_cpu_read_4(__preempt_count) & PREEMPT_NEED_RESCHED);
|
|
}
|
|
|
|
/*
|
|
* The various preempt_count add/sub methods
|
|
*/
|
|
|
|
static __always_inline void __preempt_count_add(int val)
|
|
{
|
|
__this_cpu_add_4(__preempt_count, val);
|
|
}
|
|
|
|
static __always_inline void __preempt_count_sub(int val)
|
|
{
|
|
__this_cpu_add_4(__preempt_count, -val);
|
|
}
|
|
|
|
/*
|
|
* Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule
|
|
* a decrement which hits zero means we have no preempt_count and should
|
|
* reschedule.
|
|
*/
|
|
static __always_inline bool __preempt_count_dec_and_test(void)
|
|
{
|
|
GEN_UNARY_RMWcc("decl", __preempt_count, __percpu_arg(0), "e");
|
|
}
|
|
|
|
/*
|
|
* Returns true when we need to resched and can (barring IRQ state).
|
|
*/
|
|
static __always_inline bool should_resched(void)
|
|
{
|
|
return unlikely(!__this_cpu_read_4(__preempt_count));
|
|
}
|
|
|
|
#ifdef CONFIG_PREEMPT
|
|
extern asmlinkage void ___preempt_schedule(void);
|
|
# define __preempt_schedule() asm ("call ___preempt_schedule")
|
|
extern asmlinkage void preempt_schedule(void);
|
|
# ifdef CONFIG_CONTEXT_TRACKING
|
|
extern asmlinkage void ___preempt_schedule_context(void);
|
|
# define __preempt_schedule_context() asm ("call ___preempt_schedule_context")
|
|
# endif
|
|
#endif
|
|
|
|
#endif /* __ASM_PREEMPT_H */
|