Messages in this thread | | | Date | Thu, 27 Apr 2017 19:01:04 +0100 | From | Will Deacon <> | Subject | Re: [PATCHv2 2/2] arm64: cpufeature: use static_branch_enable_cpuslocked() |
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On Thu, Apr 27, 2017 at 06:44:37PM +0100, Mark Rutland wrote: > Recently, the hotplug locking was conveted to use a percpu rwsem. Unlike > the existing {get,put}_online_cpus() logic, this can't nest. > Unfortunately, in arm64's secondary boot path we can end up nesting via > static_branch_enable() in cpus_set_cap() when we detect an erratum. > > This leads to a stream of messages as below, where the secondary > attempts to schedule before it has been fully onlined. As the CPU > orchestrating the onlining holds the rswem, this hangs the system. > > [ 0.250334] BUG: scheduling while atomic: swapper/1/0/0x00000002 > [ 0.250337] Modules linked in: > [ 0.250346] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.11.0-rc7-next-20170424 #2 > [ 0.250349] Hardware name: ARM Juno development board (r1) (DT) > [ 0.250353] Call trace: > [ 0.250365] [<ffff000008088510>] dump_backtrace+0x0/0x238 > [ 0.250371] [<ffff00000808880c>] show_stack+0x14/0x20 > [ 0.250377] [<ffff00000839d854>] dump_stack+0x9c/0xc0 > [ 0.250384] [<ffff0000080e3540>] __schedule_bug+0x50/0x70 > [ 0.250391] [<ffff000008932ecc>] __schedule+0x52c/0x5a8 > [ 0.250395] [<ffff000008932f80>] schedule+0x38/0xa0 > [ 0.250400] [<ffff000008935e8c>] rwsem_down_read_failed+0xc4/0x108 > [ 0.250407] [<ffff0000080fe8e0>] __percpu_down_read+0x100/0x118 > [ 0.250414] [<ffff0000080c0b60>] get_online_cpus+0x70/0x78 > [ 0.250420] [<ffff0000081749e8>] static_key_enable+0x28/0x48 > [ 0.250425] [<ffff00000808de90>] update_cpu_capabilities+0x78/0xf8 > [ 0.250430] [<ffff00000808d14c>] update_cpu_errata_workarounds+0x1c/0x28 > [ 0.250435] [<ffff00000808e004>] check_local_cpu_capabilities+0xf4/0x128 > [ 0.250440] [<ffff00000808e894>] secondary_start_kernel+0x8c/0x118 > [ 0.250444] [<000000008093d1b4>] 0x8093d1b4 > > We call cpus_set_cap() from update_cpu_capabilities(), which is called > from the secondary boot path (where the CPU orchestrating the onlining > holds the hotplug rwsem), and in the primary boot path, where this is > not held. > > This patch makes cpus_set_cap() use static_branch_enable_cpuslocked(), > and updates all the callers of update_cpu_capabilities() consistent with > the change. > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Reported-by: Catalin Marinas <catalin.marinas@arm.com> > Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > Suggested-by: Thomas Gleixner <tglx@linutronix.de> > Cc: Will Deacon <will.deacon@arm.com> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> > [Mark: minor fixups] > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > --- > arch/arm64/include/asm/cpufeature.h | 5 +++-- > arch/arm64/kernel/cpu_errata.c | 13 ++++++++++++- > arch/arm64/kernel/cpufeature.c | 5 ++++- > arch/arm64/kernel/smp.c | 7 +++---- > 4 files changed, 22 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h > index f31c48d..c96353a 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]); > } > } > > @@ -222,7 +222,8 @@ void update_cpu_capabilities(const struct arm64_cpu_capabilities *caps, > void enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps); > void check_local_cpu_capabilities(void); > > -void update_cpu_errata_workarounds(void); > +void update_secondary_cpu_errata_workarounds(void); > +void update_boot_cpu_errata_workarounds(void); > void __init enable_errata_workarounds(void); > void verify_local_cpu_errata_workarounds(void); > > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c > index f6cc67e..379ad8d 100644 > --- a/arch/arm64/kernel/cpu_errata.c > +++ b/arch/arm64/kernel/cpu_errata.c > @@ -175,9 +175,20 @@ void verify_local_cpu_errata_workarounds(void) > } > } > > -void update_cpu_errata_workarounds(void) > +/* > + * Secondary CPUs are booted with the waker holding the > + * CPU hotplug lock, hence we don't need to lock it here again. > + */ > +void update_secondary_cpu_errata_workarounds(void) > +{ > + update_cpu_capabilities(arm64_errata, "enabling workaround for"); > +} > + > +void update_boot_cpu_errata_workarounds(void) > { > + get_online_cpus(); > update_cpu_capabilities(arm64_errata, "enabling workaround for"); > + put_online_cpus(); > }
These functions seem to have unhelpful names, especially when compared to the naming scheme used by the core code. I'd prefer to have:
update_cpu_errata_workarounds: just calls update_cpu_capabilities
update_cpu_errata_workarounds_cpuslocked: does get_online_cpus(), then calls update_cpu_errata_workarounds, then does put_online_cpus();
With that change:
Acked-by: Will Deacon <will.deacon@arm.com>
for -tip.
Will
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