Andrew Morton wrote:
> On Sun, 29 Jul 2007 13:29:26 +0300
> Avi Kivity <[email protected]> wrote:
>
>
>> If a cpu is spinning in the kernel but still responding to interrupts,
>> pressing sysrq-y will show you where it's spinning.
>>
>> Signed-off-by: Avi Kivity <[email protected]>
>>
>> diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c
>> index 39cc318..1dda709 100644
>> --- a/drivers/char/sysrq.c
>> +++ b/drivers/char/sysrq.c
>> @@ -45,6 +45,8 @@ int __read_mostly __sysrq_enabled = 1;
>>
>> static int __read_mostly sysrq_always_enabled;
>>
>> +static spinlock_t show_stack_lock = SPIN_LOCK_UNLOCKED;
>>
>
> Use DEFINE_SPINLOCK to avoid confusing lockdep.
>
>
Okay.
>> int sysrq_on(void)
>> {
>> return __sysrq_enabled || sysrq_always_enabled;
>> @@ -309,6 +311,26 @@ static struct sysrq_key_op sysrq_unrt_op = {
>> .enable_mask = SYSRQ_ENABLE_RTNICE,
>> };
>>
>> +static void show_cpu_stack(void *garbage)
>> +{
>> + spin_lock(&show_stack_lock);
>> + printk("CPU%d stacktrace:\n", raw_smp_processor_id());
>> + dump_stack();
>> + sysrq_handle_showregs(0, NULL);
>> + spin_unlock(&show_stack_lock);
>> +}
>> +
>> +static void sysrq_show_stacks(int key, struct tty_struct *tty)
>> +{
>> + on_each_cpu(show_cpu_stack, NULL, 0, 1);
>> +}
>> +
>> +static struct sysrq_key_op sysrq_show_stacks_op = {
>> + .handler = sysrq_show_stacks,
>> + .help_msg = "stacktraces-on-all-cpus(Y)",
>> + .action_msg = "Stack traces on all cpus",
>> +};
>> +
>> /* Key Operations table and lock */
>> static DEFINE_SPINLOCK(sysrq_key_table_lock);
>>
>> @@ -356,7 +378,7 @@ static struct sysrq_key_op *sysrq_key_table[36] = {
>> &sysrq_showstate_blocked_op, /* w */
>> /* x: May be registered on ppc/powerpc for xmon */
>> NULL, /* x */
>> - NULL, /* y */
>> + &sysrq_show_stacks_op, /* y */
>> NULL /* z */
>> };
>>
>>
>
> but, but.. sysrq handlers called from hard IRQ. Are we sure that none of
> the drivers which call into the sysrq code do so with hard IRQs disabled?
>
> Because if we call on_each_cpu() with hard IRQs disabled, the various
> implementations will emit loud warnings due to the deadlockability.
>
>
Ah, I tested this with /proc/sysrq-trigger.
Maybe we should temporarily enable irqs here; if you press this key,
your system is already on the way out anyway. But perhaps that would
entrap curious admins checking out what the keys do.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
