Messages in this thread Patch in this message | | | Date | Fri, 13 Nov 2020 16:58:43 +0000 | From | Ionela Voinescu <> | Subject | Re: [PATCH] arm64: abort counter_read_on_cpu() when irqs_disabled() |
| |
On Friday 13 Nov 2020 at 16:02:34 (+0000), Mark Rutland wrote: > On Fri, Nov 13, 2020 at 03:53:28PM +0000, Ionela Voinescu wrote: > > Given that smp_call_function_single() can deadlock when interrupts are > > disabled, abort the SMP call if irqs_disabled(). This scenario is > > currently not possible given the function's uses, but safeguard this for > > potential future uses. > > Sorry to contradict earlier feedback, but I think this is preferable > as-is, since smp_call_function_single() will > WARN_ON_ONCE(irqs_disabled())), but this will silently mask any dodgy > usage.
Probably it only contradicts the chosen implementation.
> > If we want a separate check here, I reckon we should wrap it with a > WARN_ON_ONCE(), and only relax that if/when we have a legitimate case > for calling this with IRQs disabled. >
That's fair. I'll replace the condition below with:
if (!cpu_has_amu_feat(cpu)) return -EOPNOTSUPP;
if (WARN_ON_ONCE(irqs_disabled()) return -EPERM;
Thanks for your time, Ionela.
> Thanks, > Mark. > > > > > Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com> > > Cc: Catalin Marinas <catalin.marinas@arm.com> > > Cc: Will Deacon <will@kernel.org> > > --- > > arch/arm64/kernel/topology.c | 6 +++++- > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > > index 3a083a9a8ef2..e387188741f2 100644 > > --- a/arch/arm64/kernel/topology.c > > +++ b/arch/arm64/kernel/topology.c > > @@ -343,7 +343,11 @@ static void cpu_read_constcnt(void *val) > > static inline > > int counters_read_on_cpu(int cpu, smp_call_func_t func, u64 *val) > > { > > - if (!cpu_has_amu_feat(cpu)) > > + /* > > + * Abort call on counterless CPU or when interrupts are > > + * disabled - can lead to deadlock in smp sync call. > > + */ > > + if (!cpu_has_amu_feat(cpu) || unlikely(irqs_disabled())) > > return -EOPNOTSUPP; > > > > smp_call_function_single(cpu, func, val, 1); > > -- > > 2.17.1 > >
| |