> -----Original Message-----
> From: Colin Cross [mailto:ccr...@android.com]
> Sent: 2013年8月24日 3:45
> To: linux...@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org; Neil Zhang; Joseph Lo;
> linux-te...@vger.kernel.org; Colin Cross; sta...@vger.kernel.org; Rafael J.
> Wysocki; Daniel Lezcano
> Subject: [PATCH 3/3] cpuidle: coupled: fix race condition between pokes and
> safe
> state
>
> The coupled cpuidle waiting loop clears pending pokes before entering the safe
> state. If a poke arrives just before the pokes are cleared, but after the
> while
> loop condition checks, the poke will be lost and the cpu will stay in the
> safe state
> until another interrupt arrives. This may cause the cpu that sent the poke to
> spin in the ready loop with interrupts off until another cpu receives an
> interrupt,
> and if no other cpus have interrupts routed to them it can spin forever.
>
> Change the return value of cpuidle_coupled_clear_pokes to return if a poke was
> cleared, and move the need_resched() checks into the callers. In the waiting
> loop, if a poke was cleared restart the loop to repeat the while condition
> checks.
>
> Reported-by: Neil Zhang <zhan...@marvell.com>
> CC: sta...@vger.kernel.org
> Signed-off-by: Colin Cross <ccr...@android.com>
> ---
> drivers/cpuidle/coupled.c | 20 ++++++++++++++------
> 1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c index
> bbc4ba5..c91230b 100644
> --- a/drivers/cpuidle/coupled.c
> +++ b/drivers/cpuidle/coupled.c
> @@ -408,19 +408,22 @@ static void cpuidle_coupled_set_done(int cpu, struct
> cpuidle_coupled *coupled)
> * been processed and the poke bit has been cleared.
> *
> * Other interrupts may also be processed while interrupts are enabled, so
> - * need_resched() must be tested after turning interrupts off again to make
> sure
> + * need_resched() must be tested after this function returns to make
> + sure
> * the interrupt didn't schedule work that should take the cpu out of idle.
> *
> - * Returns 0 if need_resched was false, -EINTR if need_resched was true.
> + * Returns 0 if no poke was pending, 1 if a poke was cleared.
> */
> static int cpuidle_coupled_clear_pokes(int cpu) {
> + if (!cpumask_test_cpu(cpu, &cpuidle_coupled_poke_pending))
> + return 0;
> +
> local_irq_enable();
> while (cpumask_test_cpu(cpu, &cpuidle_coupled_poke_pending))
> cpu_relax();
> local_irq_disable();
>
> - return need_resched() ? -EINTR : 0;
> + return 1;
> }
>
> static bool cpuidle_coupled_any_pokes_pending(struct cpuidle_coupled
> *coupled) @@ -464,7 +467,8 @@ int cpuidle_enter_state_coupled(struct
> cpuidle_device *dev,
> return -EINVAL;
>
> while (coupled->prevent) {
> - if (cpuidle_coupled_clear_pokes(dev->cpu)) {
> + cpuidle_coupled_clear_pokes(dev->cpu);
> + if (need_resched()) {
> local_irq_enable();
> return entered_state;
> }
> @@ -503,7 +507,10 @@ retry:
> */
> while (!cpuidle_coupled_cpus_waiting(coupled) ||
> !cpumask_test_cpu(dev->cpu, &cpuidle_coupled_poked)) {
> - if (cpuidle_coupled_clear_pokes(dev->cpu)) {
> + if (cpuidle_coupled_clear_pokes(dev->cpu))
> + continue;
> +
> + if (need_resched()) {
> cpuidle_coupled_set_not_waiting(dev->cpu, coupled);
> goto out;
> }
> @@ -518,7 +525,8 @@ retry:
> local_irq_disable();
> }
>
> - if (cpuidle_coupled_clear_pokes(dev->cpu)) {
> + cpuidle_coupled_clear_pokes(dev->cpu);
> + if (need_resched()) {
> cpuidle_coupled_set_not_waiting(dev->cpu, coupled);
> goto out;
> }
> --
> 1.8.3
I think this patch should also be workable.
Thanks.
Reviewed-by: Neil Zhang <zhan...@marvell.com>
Best Regards,
Neil Zhang
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