Commit b268264c authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Linus Torvalds

[PATCH] sched: fix preemption race (Core/i386)

The idle-thread-preemption-fix.patch introduced a race, which is not
critical, but might give us an extra turn through the scheduler.  When
interrupts are reenabled in entry.c and an interrupt occures before we
reach the add_preempt_schedule() in preempt_schedule we get rescheduled
again in the return from interrupt path.

The patch prevents this by leaving interrupts disabled and calling a a
seperate function preempt_schedule_irq().

This split adds different plausibility checks for irq context calls and
kernel calls.
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 1b7c3647
...@@ -176,6 +176,7 @@ ENTRY(resume_userspace) ...@@ -176,6 +176,7 @@ ENTRY(resume_userspace)
#ifdef CONFIG_PREEMPT #ifdef CONFIG_PREEMPT
ENTRY(resume_kernel) ENTRY(resume_kernel)
cli
cmpl $0,TI_preempt_count(%ebp) # non-zero preempt_count ? cmpl $0,TI_preempt_count(%ebp) # non-zero preempt_count ?
jnz restore_all jnz restore_all
need_resched: need_resched:
...@@ -184,10 +185,7 @@ need_resched: ...@@ -184,10 +185,7 @@ need_resched:
jz restore_all jz restore_all
testl $IF_MASK,EFLAGS(%esp) # interrupts off (exception path) ? testl $IF_MASK,EFLAGS(%esp) # interrupts off (exception path) ?
jz restore_all jz restore_all
sti call preempt_schedule_irq
call preempt_schedule
cli
movl $0,TI_preempt_count(%ebp)
jmp need_resched jmp need_resched
#endif #endif
......
...@@ -2867,6 +2867,48 @@ asmlinkage void __sched preempt_schedule(void) ...@@ -2867,6 +2867,48 @@ asmlinkage void __sched preempt_schedule(void)
} }
EXPORT_SYMBOL(preempt_schedule); EXPORT_SYMBOL(preempt_schedule);
/*
* this is is the entry point to schedule() from kernel preemption
* off of irq context.
* Note, that this is called and return with irqs disabled. This will
* protect us against recursive calling from irq.
*/
asmlinkage void __sched preempt_schedule_irq(void)
{
struct thread_info *ti = current_thread_info();
#ifdef CONFIG_PREEMPT_BKL
struct task_struct *task = current;
int saved_lock_depth;
#endif
/* Catch callers which need to be fixed*/
BUG_ON(ti->preempt_count || !irqs_disabled());
need_resched:
add_preempt_count(PREEMPT_ACTIVE);
/*
* We keep the big kernel semaphore locked, but we
* clear ->lock_depth so that schedule() doesnt
* auto-release the semaphore:
*/
#ifdef CONFIG_PREEMPT_BKL
saved_lock_depth = task->lock_depth;
task->lock_depth = -1;
#endif
local_irq_enable();
schedule();
local_irq_disable();
#ifdef CONFIG_PREEMPT_BKL
task->lock_depth = saved_lock_depth;
#endif
sub_preempt_count(PREEMPT_ACTIVE);
/* we could miss a preemption opportunity between schedule and now */
barrier();
if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))
goto need_resched;
}
#endif /* CONFIG_PREEMPT */ #endif /* CONFIG_PREEMPT */
int default_wake_function(wait_queue_t *curr, unsigned mode, int sync, void *key) int default_wake_function(wait_queue_t *curr, unsigned mode, int sync, void *key)
......
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