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schedule(): hold runq lock for the entire duration of context switching

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releasing the runq lock after loading page tables but before the actual
context switch can leave execution in an inconsistent if the current
process is descheduled from an IRQ between these two steps.
this patch holds the runq lock with IRQs disabled and makes the context
switch a single atomic operation.
This commit is contained in:
Balazs Gerofi
2015-08-10 12:37:12 +09:00
parent 8d6c97ea5c
commit 9ba40dc0ff
4 changed files with 34 additions and 5 deletions
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25
kernel/process.c
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@@ -2062,6 +2062,12 @@ static void do_migrate(void);
static void idle(void)
{
struct cpu_local_var *v = get_this_cpu_local_var();
/* Release runq_lock before starting the idle loop.
* See comments at release_runq_lock().
*/
ihk_mc_spinlock_unlock(&(cpu_local_var(runq_lock)),
cpu_local_var(runq_irqstate));
if(v->status == CPU_STATUS_RUNNING)
v->status = CPU_STATUS_IDLE;
@@ -2236,7 +2242,6 @@ void schedule(void)
struct cpu_local_var *v;
struct process *next, *prev, *proc, *tmp = NULL;
int switch_ctx = 0;
unsigned long irqstate;
struct process *last;
if (cpu_local_var(no_preempt)) {
@@ -2250,7 +2255,8 @@ void schedule(void)
}
redo:
irqstate = ihk_mc_spinlock_lock(&(get_this_cpu_local_var()->runq_lock));
cpu_local_var(runq_irqstate) =
ihk_mc_spinlock_lock(&(get_this_cpu_local_var()->runq_lock));
v = get_this_cpu_local_var();
next = NULL;
@@ -2337,14 +2343,22 @@ redo:
/* Set up new TLS.. */
do_arch_prctl(ARCH_SET_FS, next->thread.tlsblock_base);
ihk_mc_spinlock_unlock(&(v->runq_lock), irqstate);
if (prev) {
last = ihk_mc_switch_context(&prev->ctx, &next->ctx, prev);
}
else {
last = ihk_mc_switch_context(NULL, &next->ctx, prev);
}
/*
* We must hold the lock throughout the context switch, otherwise
* an IRQ could deschedule this process between page table loading and
* context switching and leave the execution in an inconsistent state.
* Since we may be migrated to another core meanwhile, we refer
* directly to cpu_local_var.
*/
ihk_mc_spinlock_unlock(&(cpu_local_var(runq_lock)),
cpu_local_var(runq_irqstate));
/* Have we migrated to another core meanwhile? */
if (v != get_this_cpu_local_var()) {
@@ -2358,7 +2372,8 @@ redo:
}
}
else {
ihk_mc_spinlock_unlock(&(v->runq_lock), irqstate);
ihk_mc_spinlock_unlock(&(cpu_local_var(runq_lock)),
cpu_local_var(runq_irqstate));
}
}