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Groups > linux.kernel > #1632007
| From | Mark Rutland <mark.rutland@arm.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem |
| Date | 2017-04-27 12:00 +0200 |
| Message-ID | <tAOnn-7ap-5@gated-at.bofh.it> (permalink) |
| References | (2 earlier) <tAcrM-7Dc-23@gated-at.bofh.it> <tAr7s-bV-25@gated-at.bofh.it> <tArTQ-yp-19@gated-at.bofh.it> <tAswy-11B-19@gated-at.bofh.it> <tAMYj-6lN-43@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Thu, Apr 27, 2017 at 10:27:20AM +0200, Sebastian Siewior wrote:
> On 2017-04-26 11:32:36 [+0100], Mark Rutland wrote:
> > > So we could end up calling static_branch_enable_cpuslocked()
> > > without actually holding the lock. Should we do a cpu_hotplug_begin/done in
> > > setup_cpu_feature_capabilities ? I agree it doesn't look that nice. Thoughts ?
> >
> > I agree that's hideous, but it looks like the only choice given the
> > hotplug rwsem cahnges. :/
>
> would work for you to provide a locked and unlocked version?
Maybe. Today we have:
// rwsem unlocked
start_kernel()
->smp_prepare_boot_cpu()
-->update_cpu_errata_workarounds()
--->update_cpu_capabilities()
// rwsem locked (by other CPU)
secondary_start_kernel()
->check_local_cpu_capabilities()
-->update_cpu_errata_workarounds()
--->update_cpu_capabilities()
With the common chain:
update_cpu_capabilities()
->cpus_set_cap()
-->static_branch_enable()
... so we could add a update_cpu_capabilities{,_cpuslocked}(), and say
that cpus_set_cap() expects the hotplug rswem to be locked, as per the
below diff.
Thoughts?
Mark.
---->8----
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index f31c48d..7341579 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -145,7 +145,7 @@ static inline void cpus_set_cap(unsigned int num)
num, ARM64_NCAPS);
} else {
__set_bit(num, cpu_hwcaps);
- static_branch_enable(&cpu_hwcap_keys[num]);
+ static_branch_enable_cpuslocked(&cpu_hwcap_keys[num]);
}
}
@@ -217,8 +217,22 @@ static inline bool id_aa64pfr0_32bit_el0(u64 pfr0)
void __init setup_cpu_features(void);
-void update_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
- const char *info);
+void __update_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
+ const char *info, bool cpuslocked);
+static inline void
+update_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
+ const char *info)
+{
+ __update_cpu_capabilities(caps, info, false);
+}
+
+static inline void
+update_cpu_capabilities_cpuslocked(const struct arm64_cpu_capabilities *caps,
+ const char *info)
+{
+ __update_cpu_capabilities(caps, info, true);
+}
+
void enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps);
void check_local_cpu_capabilities(void);
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index abda8e8..ae8ddc1 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -956,8 +956,8 @@ static void __init setup_elf_hwcaps(const struct arm64_cpu_capabilities *hwcaps)
cap_set_elf_hwcap(hwcaps);
}
-void update_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
- const char *info)
+void __update_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
+ const char *info, bool cpuslocked)
{
for (; caps->matches; caps++) {
if (!caps->matches(caps, caps->def_scope))
@@ -965,7 +965,14 @@ void update_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
if (!cpus_have_cap(caps->capability) && caps->desc)
pr_info("%s %s\n", info, caps->desc);
- cpus_set_cap(caps->capability);
+
+ if (cpuslocked) {
+ cpus_set_cap(caps->capability);
+ } else {
+ get_online_cpus();
+ cpus_set_cap(caps->capability);
+ put_online_cpus();
+ }
}
}
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Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Mark Rutland <mark.rutland@arm.com> - 2017-04-25 18:20 +0200
Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Sebastian Siewior <bigeasy@linutronix.de> - 2017-04-25 19:30 +0200
Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Mark Rutland <mark.rutland@arm.com> - 2017-04-26 11:10 +0200
Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Suzuki K Poulose <Suzuki.Poulose@arm.com> - 2017-04-26 12:00 +0200
Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Mark Rutland <mark.rutland@arm.com> - 2017-04-26 12:40 +0200
Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Sebastian Siewior <bigeasy@linutronix.de> - 2017-04-27 10:30 +0200
Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Mark Rutland <mark.rutland@arm.com> - 2017-04-27 12:00 +0200
Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Thomas Gleixner <tglx@linutronix.de> - 2017-04-27 12:10 +0200
Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Mark Rutland <mark.rutland@arm.com> - 2017-04-27 14:40 +0200
[PATCH] arm64: cpufeature: use static_branch_enable_cpuslocked() (was: Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem) Mark Rutland <mark.rutland@arm.com> - 2017-04-27 17:50 +0200
Re: [PATCH] arm64: cpufeature: use static_branch_enable_cpuslocked() (was: Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem) Suzuki K Poulose <Suzuki.Poulose@arm.com> - 2017-04-27 18:40 +0200
Re: [PATCH] arm64: cpufeature: use static_branch_enable_cpuslocked() Suzuki K Poulose <Suzuki.Poulose@arm.com> - 2017-04-27 19:10 +0200
Re: [PATCH] arm64: cpufeature: use static_branch_enable_cpuslocked() Mark Rutland <mark.rutland@arm.com> - 2017-04-27 19:20 +0200
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