Messages in this thread | | | Date | Tue, 01 Aug 2017 09:28:29 -0300 | From | Victor Aoqui <> | Subject | Re: [PATCH] drivers: cpuidle: Disable preemption before get_lppaca function call in pseries_idle_probe function |
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Em 2017-07-20 18:21, Benjamin Herrenschmidt escreveu: > 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 [00000000] 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 >> lppaca_shared_proc(get_lppaca()). > > 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 > more drastic... > > 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. > > Ben.
Hi Benjamin,
Sorry for the delay. I was a little bit busy last days. I took note of your comments and I will work on those changes. I will let you know soon when it's done.
Thanks
-- Victor Aoqui
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