Hi Corey, Chengfeng,
On Wed, 28 Jun 2023, at 21:17, Corey Minyard wrote:
> Indeed, this looks like an issue.
>
> Andrew, any opinions on this? The attached patch will work, the other
> option would be to disable interrupts when calling
> kcs_bmc_handle_event() in the timer handler. But then you have to worry
> about RT.
Right, I think we'd do best to not over-complicate things.
spin_lock_irq{save,restore}() are the intuitive choice to me.
I'll follow up with R-b/T-b tags once I've booted the patch
and done some testing.
Andrew
>
> -corey
>
> On Tue, Jun 27, 2023 at 03:24:49PM +0000, Chengfeng Ye wrote:
>> As kcs_bmc_handle_event() is executed inside both a timer and a hardirq,
>> it should disable irq before lock acquisition otherwise deadlock could
>> happen if the timmer is preemtped by the irq.
>>
>> Possible deadlock scenario:
>> aspeed_kcs_check_obe() (timer)
>> -> kcs_bmc_handle_event()
>> -> spin_lock(&kcs_bmc->lock)
>> <irq interruption>
>> -> aspeed_kcs_irq()
>> -> kcs_bmc_handle_event()
>> -> spin_lock(&kcs_bmc->lock) (deadlock here)
>>
>> This flaw was found using an experimental static analysis tool we are
>> developing for irq-related deadlock.
>>
>> The tentative patch fix the potential deadlock by spin_lock_irqsave()
>>
>> Signed-off-by: Chengfeng Ye <[email protected]>
>> ---
>> drivers/char/ipmi/kcs_bmc.c | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/char/ipmi/kcs_bmc.c b/drivers/char/ipmi/kcs_bmc.c
>> index 03d02a848f3a..8b1161d5194a 100644
>> --- a/drivers/char/ipmi/kcs_bmc.c
>> +++ b/drivers/char/ipmi/kcs_bmc.c
>> @@ -56,12 +56,13 @@ irqreturn_t kcs_bmc_handle_event(struct kcs_bmc_device
>> *kcs_bmc)
>> {
>> struct kcs_bmc_client *client;
>> irqreturn_t rc = IRQ_NONE;
>> + unsigned long flags;
>>
>> - spin_lock(&kcs_bmc->lock);
>> + spin_lock_irqsave(&kcs_bmc->lock, flags);
>> client = kcs_bmc->client;
>> if (client)
>> rc = client->ops->event(client);
>> - spin_unlock(&kcs_bmc->lock);
>> + spin_unlock_irqrestore(&kcs_bmc->lock, flags);
>>
>> return rc;
>> }
>> --
>> 2.17.1
>>
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