[PATCH] drivers: cpuidle: Disable preemption before get_lppaca function call in pseries_idle_probe function
benh at kernel.crashing.org
Fri Jul 21 07:21:53 AEST 2017
On Thu, 2017-07-20 at 14:57 -0300, Victor Aoqui wrote:
> When CONFIG_PREEMPT=y, the following warning shows up:
> BUG: using smp_processor_id() in preemptible  code: swapper/0/1
> caller is pseries_processor_idle_init+0x58/0x21c
> This warning shows up because preemption cannot occur when using
> get_paca(), otherwise the paca_struct it points to may be the wrong one
> just after.
> For this reason, preemption needs to be disabled before
Also chekc the generated assembly. We had all sort of interesting
issues where gcc would copy the paca pointer or the lppaca pointer
to a GPR *outside* of the preempt disabled section...
In that specific case it's not a big deal but overall, I am not
comfortable with PREEMPT on powerpc until we do something a bit
I would like to remove all such direct accesses to paca, instead have a
"new" get_paca() written in asm that does the preempt disable then
returns the PACA in a GPR (not directly use r13, hide that from gcc),
and which is paired with a put_paca().
The few places where we want to directly access r13 should be hand
written in asm too to hide r13 from gcc, for accessing the irq_happened
in the fast path of local_irq_enable/disable/... we should do the same
with lock tokens.
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