[PATCH] arm64: abort counter_read_on_cpu() when irqs_disabled()
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.
Signed-off-by: Ionela Voinescu
Cc: Catalin Marinas
Cc: Will Deacon
---
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
Re: [PATCH] arm64: abort counter_read_on_cpu() when irqs_disabled()
On Fri, Nov 13, 2020 at 04:58:43PM +, Ionela Voinescu wrote: > On Friday 13 Nov 2020 at 16:02:34 (+), Mark Rutland wrote: > > On Fri, Nov 13, 2020 at 03:53:28PM +, 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; That'd be great, thanks! With that, feel free to add: Acked-by: Mark Rutland Mark.
Re: [PATCH] arm64: abort counter_read_on_cpu() when irqs_disabled()
On Fri, Nov 13, 2020 at 04:58:43PM +, Ionela Voinescu wrote: > On Friday 13 Nov 2020 at 16:02:34 (+), Mark Rutland wrote: > > On Fri, Nov 13, 2020 at 03:53:28PM +, 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; Works for me. Thanks. -- Catalin
Re: [PATCH] arm64: abort counter_read_on_cpu() when irqs_disabled()
On Fri, Nov 13, 2020 at 03:53:28PM +, 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
> Cc: Catalin Marinas
> Cc: Will Deacon
> ---
> 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
>
Re: [PATCH] arm64: abort counter_read_on_cpu() when irqs_disabled()
On Friday 13 Nov 2020 at 16:02:34 (+), Mark Rutland wrote:
> On Fri, Nov 13, 2020 at 03:53:28PM +, 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
> > Cc: Catalin Marinas
> > Cc: Will Deacon
> > ---
> > 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
> >
