BUG: scheduling while atomic

[Srivatsa S. Bhat]

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.

 

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.

Regards,
Srivatsa S. Bhat