BUG: scheduling while atomic

[Arun KS]

Hi Srivatsa,

On Wed, Apr 18, 2012 at 1:57 PM, Srivatsa S. Bhat <
srivatsa.bhat at linux.vnet.ibm.com> wrote:

> On 04/18/2012 01:38 PM, Arun KS wrote:
>
> > Hi Dave,
> >
> > Thanks for your reply.
> >
> > On Wed, Apr 18, 2012 at 1:01 PM, Dave Hylands <dhylands at gmail.com
> > <mailto:dhylands at gmail.com>> wrote:
> >
> >     Hi Arun,
> >
> >     On Tue, Apr 17, 2012 at 11:44 PM, Arun KS <getarunks at gmail.com
> >     <mailto:getarunks at gmail.com>> wrote:
> >     >
> >     > Hello Guys,
> >     >
> >     > System is working normal after this BUG.
> >     > PC is at 0x400b4614, probably a mmaped address.
> >     >
> >     > Just wondering how can this BUG happen when a process is running
> >     in user
> >     > space.
> >     >
> >     > Can it be something like this
> >     > 1) enter to kernel from userspace through some system call.
> >     > 2) kernel disables the interrupt and return to user space.
> >
> >     Don't do that
> >
> >
> > I don't do that. This scenario mentioned is a just a wild guess.
> >
> >
> >     > 3) and now it can happen in user space?
> >
> >     Because something in userspace made a blocking call which would cause
> >     a context switch to occur and your driver erroneously left interrupts
> >     disabled.
> >
> > In that case, my system should have been unstable afterwards if
> > interrupts are left disabled. But that is not happening.
> >
> > If we return to user space with interrupts disabled, can we switch back
> > again to kernel using a system cal(because interrupts are already
> disabled)?
> >
>
>
> Depends on how many CPUs you have - AFAICS the "interrupts disabled"
> discussion above applies to a single CPU.. so if you have other CPUs on
> your
> system, you could probably use the system for a little more time.
>
>
> Hmm.. I have uniprocessor.

>
> There is a simple way to check if interrupts are indeed disabled as
> hypothesised: turn on the hard-lockup detector (See
> Documentation/lockup-watchdogs.txt for details on what it is and what
> config options you have to enable). You can even turn on the soft-lockup
> detector and see what you get. Setting the option to panic on hard-lockup/
> soft-lockup/hung tasks would be even better, to debug the issue.
>

Thanks for the pointers. I ll try this out.

Arun

>
> Regards,
> Srivatsa S. Bhat
>
>
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