| Message ID | 20201113155328.4194-1-ionela.voinescu@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: abort counter_read_on_cpu() when irqs_disabled() | expand |
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 <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 >
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 > >
On Fri, Nov 13, 2020 at 04:58:43PM +0000, Ionela Voinescu wrote: > 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; That'd be great, thanks! With that, feel free to add: Acked-by: Mark Rutland <mark.rutland@arm.com> Mark.
On Fri, Nov 13, 2020 at 04:58:43PM +0000, Ionela Voinescu wrote: > 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; Works for me. Thanks.
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);
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 <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(-)