[PATCH] ARM: Fix "BUG: scheduling while atomic: swapper/0/0x00000002"

[Shilimkar, Santosh]

> -----Original Message-----
> From: Russell King - ARM Linux [mailto:linux at arm.linux.org.uk]
> Sent: Wednesday, March 17, 2010 2:20 AM
> To: Shilimkar, Santosh
> Cc: linux-arm-kernel at lists.infradead.org; Catalin Marinas
> Subject: Re: [PATCH] ARM: Fix "BUG: scheduling while atomic: swapper/0/0x00000002"
> 
> On Tue, Mar 16, 2010 at 06:42:29PM +0530, Santosh Shilimkar wrote:
> > This patch fixes the preempt leak in the cpuidle path invoked from
> > cpu-hotplug
> > log:
> > BUG: scheduling while atomic: swapper/0/0x00000002
> > <d>Modules linked in:
> > Backtrace:
> > [<c0024f90>] (dump_backtrace+0x0/0x110) from [<c01762c4>] (dump_stack+0x18/0x1c)
> >  r7:c0218cc4 r6:c0341f00 r5:c7836000 r4:00000000
> > [<c01762ac>] (dump_stack+0x0/0x1c) from [<c003d94c>] (__schedule_bug+0x60/0x70)
> > [<c003d8ec>] (__schedule_bug+0x0/0x70) from [<c0176914>] (schedule+0x98/0x7b8)
> >  r5:c7836000 r4:c7836000
> > [<c017687c>] (schedule+0x0/0x7b8) from [<c00228c4>] (cpu_idle+0xb4/0xd4)
> > # [<c0022810>] (cpu_idle+0x0/0xd4) from [<c01744e8>] (secondary_start_kernel+0xe0/0xf0)
> >  r5:c7836000 r4:c020a220
> > [<c0174408>] (secondary_start_kernel+0x0/0xf0) from [<c0031150>] (set_cpu_power_state+0x40/0x44)
> >  r7:c0218cc4 r6:00000001 r5:00000001 r4:c7836000
> > Backtrace aborted due to bad frame pointer <c7837fbc>
> 
> Can you describe the conditions which leads up to this please?

On SMP kernel with PREEMPT enabled, if you try to offline the CPU using hot-plug and then
bring it back(online), you will get this dump. Since CPU is taken out from idle thread, the
process shown is 2.

Regards,
Santosh