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. 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. Thanks, Mark. > > Signed-off-by: Ionela Voinescu <[email protected]> > Cc: Catalin Marinas <[email protected]> > Cc: Will Deacon <[email protected]> > --- > 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 >
