bugs in __schedule()

bugs in __schedule()

[gshan]

Anybody has suggestions on this crash?

[c02dc4dc] __schedule+0x654/0x788
 [c02dc6f4] schedule+0x4c/0xe4
 [c02dbe24] __compat_down+0xc8/0x12c
 [c0226b60] mv_sw_read_reg+0x178/0x17c
 [c02296fc] mvSwIntrTasklet+0x128/0x744
 [c0020afc] tasklet_action+0x7c/0xec
 [c00204f4] ___do_softirq+0x80/0x11c
 [c00205cc] __do_softirq+0x3c/0x6c
 [c00206a4] do_softirq+0x60/0x68
 [c00207a8] irq_exit+0x6c/0x94
 [c0005e1c] do_IRQ+0x88/0xa4
 [c0004b70] ret_from_except+0x0/0x18
 [c000680c] __delay+0xc/0x14
 [c0226598] mv_sw_read_smi_reg+0x84/0x1ac

Thanks,
Gavin
 [c0226adc] mv_sw_read_reg+0xf4/0x17c

Re: bugs in __schedule()

[Alexey Dobriyan]

On 6/26/07, gshan <gshan@alcatel-lucent.com> wrote:
> Anybody has suggestions on this crash?

talk to whoever supplied the following into your kernel:

> [c02dc4dc] __schedule+0x654/0x788
>  [c02dc6f4] schedule+0x4c/0xe4
>  [c02dbe24] __compat_down+0xc8/0x12c
>  [c0226b60] mv_sw_read_reg+0x178/0x17c

this

>  [c02296fc] mvSwIntrTasklet+0x128/0x744

and this.

>  [c0020afc] tasklet_action+0x7c/0xec
>  [c00204f4] ___do_softirq+0x80/0x11c
>  [c00205cc] __do_softirq+0x3c/0x6c
>  [c00206a4] do_softirq+0x60/0x68
>  [c00207a8] irq_exit+0x6c/0x94
>  [c0005e1c] do_IRQ+0x88/0xa4
>  [c0004b70] ret_from_except+0x0/0x18
>  [c000680c] __delay+0xc/0x14
>  [c0226598] mv_sw_read_smi_reg+0x84/0x1ac

Re: bugs in __schedule()

[Satyam Sharma]

Hi Gavin,

On 6/26/07, gshan <gshan@alcatel-lucent.com> wrote:
> Anybody has suggestions on this crash?
>
> [c02dc4dc] __schedule+0x654/0x788
>  [c02dc6f4] schedule+0x4c/0xe4
>  [c02dbe24] __compat_down+0xc8/0x12c
>  [c0226b60] mv_sw_read_reg+0x178/0x17c
>  [c02296fc] mvSwIntrTasklet+0x128/0x744
>  [c0020afc] tasklet_action+0x7c/0xec
>  [c00204f4] ___do_softirq+0x80/0x11c
>  [c00205cc] __do_softirq+0x3c/0x6c
>  [c00206a4] do_softirq+0x60/0x68
>  [c00207a8] irq_exit+0x6c/0x94
>  [c0005e1c] do_IRQ+0x88/0xa4
>  [c0004b70] ret_from_except+0x0/0x18
>  [c000680c] __delay+0xc/0x14
>  [c0226598] mv_sw_read_smi_reg+0x84/0x1ac

I bet you got more output than that, didn't you? :-)

Now I know this must be a "scheduling while interrupts disabled",
but why not post the whole error message?

[ Reminds me of the other thread where someone thought just mentioning
the EIP without any backtrace / other messages was enough to resolve a
boot-time panic. I agree they're all magicians on this list, but Gods they're
not ... ]

BTW I don't see "mvSwIntrTasklet" anywhere on -rc6. Is this a -mm kernel?

Cheers,
Satyam

Re: bugs in __schedule()

[gshan]

The code is written by myself. 2 questions:

1) tasklet couldn't sleep?
2) It is because the tasklet take a semaphore?

Thanks,
Gavin

Alexey Dobriyan wrote:
> On 6/26/07, gshan <gshan@alcatel-lucent.com> wrote:
>> Anybody has suggestions on this crash?
>
> talk to whoever supplied the following into your kernel:
>
>> [c02dc4dc] __schedule+0x654/0x788
>>  [c02dc6f4] schedule+0x4c/0xe4
>>  [c02dbe24] __compat_down+0xc8/0x12c
>>  [c0226b60] mv_sw_read_reg+0x178/0x17c
>
> this
>
>>  [c02296fc] mvSwIntrTasklet+0x128/0x744
>
> and this.
>
>>  [c0020afc] tasklet_action+0x7c/0xec
>>  [c00204f4] ___do_softirq+0x80/0x11c
>>  [c00205cc] __do_softirq+0x3c/0x6c
>>  [c00206a4] do_softirq+0x60/0x68
>>  [c00207a8] irq_exit+0x6c/0x94
>>  [c0005e1c] do_IRQ+0x88/0xa4
>>  [c0004b70] ret_from_except+0x0/0x18
>>  [c000680c] __delay+0xc/0x14
>>  [c0226598] mv_sw_read_smi_reg+0x84/0x1ac

Re: bugs in __schedule()

[gshan]

Here is the all output I have:

# ifconfig mgt0 10.0.51.27
BUG: scheduling while atomic: exe/0x00000101/752
caller is schedule+0x4c/0xe4
Call trace:
 [c02dc4dc] __schedule+0x654/0x788
 [c02dc6f4] schedule+0x4c/0xe4
 [c02dbe24] __compat_down+0xc8/0x12c
 [c0226b60] mv_sw_read_reg+0x178/0x17c
 [c02296fc] mvSwIntrTasklet+0x128/0x744
 [c0020afc] tasklet_action+0x7c/0xec
 [c00204f4] ___do_softirq+0x80/0x11c
 [c00205cc] __do_softirq+0x3c/0x6c
 [c00206a4] do_softirq+0x60/0x68
 [c00207a8] irq_exit+0x6c/0x94
 [c0005e1c] do_IRQ+0x88/0xa4
 [c0004b70] ret_from_except+0x0/0x18
 [c000680c] __delay+0xc/0x14
 [c0226598] mv_sw_read_smi_reg+0x84/0x1ac
 [c0226adc] mv_sw_read_reg+0xf4/0x17c


Satyam Sharma wrote:
> Hi Gavin,
>
> On 6/26/07, gshan <gshan@alcatel-lucent.com> wrote:
>> Anybody has suggestions on this crash?
>>
>> [c02dc4dc] __schedule+0x654/0x788
>>  [c02dc6f4] schedule+0x4c/0xe4
>>  [c02dbe24] __compat_down+0xc8/0x12c
>>  [c0226b60] mv_sw_read_reg+0x178/0x17c
>>  [c02296fc] mvSwIntrTasklet+0x128/0x744
>>  [c0020afc] tasklet_action+0x7c/0xec
>>  [c00204f4] ___do_softirq+0x80/0x11c
>>  [c00205cc] __do_softirq+0x3c/0x6c
>>  [c00206a4] do_softirq+0x60/0x68
>>  [c00207a8] irq_exit+0x6c/0x94
>>  [c0005e1c] do_IRQ+0x88/0xa4
>>  [c0004b70] ret_from_except+0x0/0x18
>>  [c000680c] __delay+0xc/0x14
>>  [c0226598] mv_sw_read_smi_reg+0x84/0x1ac
>
> I bet you got more output than that, didn't you? :-)
>
> Now I know this must be a "scheduling while interrupts disabled",
> but why not post the whole error message?
>
> [ Reminds me of the other thread where someone thought just mentioning
> the EIP without any backtrace / other messages was enough to resolve a
> boot-time panic. I agree they're all magicians on this list, but Gods 
> they're
> not ... ]
>
> BTW I don't see "mvSwIntrTasklet" anywhere on -rc6. Is this a -mm kernel?
>
> Cheers,
> Satyam

Re: bugs in __schedule()

[Satyam Sharma]

Hi Gavin,

On 6/26/07, gshan <gshan@alcatel-lucent.com> wrote:
> Here is the all output I have:
>
> # ifconfig mgt0 10.0.51.27
> BUG: scheduling while atomic: exe/0x00000101/752

Yup, you can't sleep in taskets, they're atomic.

> caller is schedule+0x4c/0xe4
> Call trace:
>  [c02dc4dc] __schedule+0x654/0x788
>  [c02dc6f4] schedule+0x4c/0xe4
>  [c02dbe24] __compat_down+0xc8/0x12c

So, you can't use / acquire semaphores in them. Use spinlocks.
If the shared data is also accessed from process context, use
spin_lock_bh() from the process context code.

Satyam

Re: bugs in __schedule()

[gshan]

Satyam Sharma wrote:
> Hi Gavin,
>
> On 6/26/07, gshan <gshan@alcatel-lucent.com> wrote:
>> Here is the all output I have:
>>
>> # ifconfig mgt0 10.0.51.27
>> BUG: scheduling while atomic: exe/0x00000101/752
>
> Yup, you can't sleep in taskets, they're atomic.
>
>> caller is schedule+0x4c/0xe4
>> Call trace:
>>  [c02dc4dc] __schedule+0x654/0x788
>>  [c02dc6f4] schedule+0x4c/0xe4
>>  [c02dbe24] __compat_down+0xc8/0x12c
>
> So, you can't use / acquire semaphores in them. Use spinlocks.
> If the shared data is also accessed from process context, use
> spin_lock_bh() from the process context code.
>
> Satyam
Thanks, Satyam. So I can replace the tasklet with kernel thread?

Re: bugs in __schedule()

[Satyam Sharma]

On 6/26/07, gshan <gshan@alcatel-lucent.com> wrote:
> Thanks, Satyam. So I can replace the tasklet with kernel thread?

That depends on what you want to do ...

[ BTW: I should correct a typo in my original reply -- I should've said
"scheduling while atomic", and not "scheduling while interrupts disabled"
because interrupts are _not_ disabled in bottom halves, and from your
stack backtrace it was evident that a tasklet was executing. :-) ]

Re: bugs in __schedule()

[gshan]

Satyam Sharma wrote:
> On 6/26/07, gshan <gshan@alcatel-lucent.com> wrote:
>> Thanks, Satyam. So I can replace the tasklet with kernel thread?
>
> That depends on what you want to do ...
>
> [ BTW: I should correct a typo in my original reply -- I should've said
> "scheduling while atomic", and not "scheduling while interrupts disabled"
> because interrupts are _not_ disabled in bottom halves, and from your
> stack backtrace it was evident that a tasklet was executing. :-) ]
I mean kernel thread could sleep, but tasklet can't. If so, it meet my 
requirements.

Re: bugs in __schedule()

[Satyam Sharma]

On 6/26/07, gshan <gshan@alcatel-lucent.com> wrote:
> I mean kernel thread could sleep, but tasklet can't. If so, it meet my
> requirements.

That's not really a justification to convert a tasklet to a kernel thread.
I suspect the simplest solution to your problem would be to simply
replace that semaphore with a spinlock. Other than that, we can't really
help without looking at code.

Re: bugs in __schedule()

[gshan]

Satyam Sharma wrote:
> On 6/26/07, gshan <gshan@alcatel-lucent.com> wrote:
>> I mean kernel thread could sleep, but tasklet can't. If so, it meet my
>> requirements.
>
> That's not really a justification to convert a tasklet to a kernel 
> thread.
> I suspect the simplest solution to your problem would be to simply
> replace that semaphore with a spinlock. Other than that, we can't really
> help without looking at code.
> -
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Thank you very much, Satyam. Anyway, I will do experiments. Thank you 
again :-)