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Date: Thu, 11 May 2017 14:12:11 +0100 From: Mark Rutland <mark.rutland@....com> To: linux-arm-kernel@...ts.infradead.org Cc: linux-kernel@...r.kernel.org, bigeasy@...utronix.de, catalin.marinas@....com, marc.zyngier@....com, mark.rutland@....com, peterz@...radead.org, suzuki.poulose@....com, tglx@...utronix.de, will.deacon@....com Subject: [PATCH] arm64/cpufeature: don't use mutex in bringup path Currently, cpus_set_cap() calls static_branch_enable_cpuslocked(), which must take the jump_label mutex. We call cpus_set_cap() in the secondary bringup path, from the idle thread where interrupts are disabled. Taking a mutex in this path "is a NONO" regardless of whether it's contended, and something we must avoid. Additionally, the secondary CPU doesn't hold the percpu rwsem (as this is held by the primary CPU), so this triggers a lockdep splat. This patch fixes both issues by moving the static_key poking from cpus_set_cap() into enable_cpu_capabilities(). This means that there is a period between detecting an erratum and cpus_have_const_cap(erratum) being true, but largely this is fine. Features are only enabled later regardless, and most errata workarounds are best-effort. This rework means that we can remove the *_cpuslocked() helpers added in commit d54bb72551b999dd ("arm64/cpufeature: Use static_branch_enable_cpuslocked()"). Fixes: efd9e03facd075f5 ("arm64: Use static keys for CPU features") Signed-off-by: Mark Rutland <mark.rutland@....com> Cc: Catalin Marinas <catalin.marinas@....com> Cc: Marc Zyniger <marc.zyngier@....com> Cc: Peter Zijlstra <peterz@...radead.org> Cc: Sebastian Sewior <bigeasy@...utronix.de> Cc: Suzuki Poulose <suzuki.poulose@....com> Cc: Thomas Gleixner <tglx@...utronix.de> Cc: Will Deacon <will.deacon@....com> --- arch/arm64/include/asm/cpufeature.h | 3 +-- arch/arm64/kernel/cpu_errata.c | 9 +-------- arch/arm64/kernel/cpufeature.c | 16 +++++++++++++--- 3 files changed, 15 insertions(+), 13 deletions(-) I'm not sure what to do about ARM64_WORKAROUND_CAVIUM_23154. This patch will defer enabling the workaround until all CPUs are up, and I can't see a good way of having the workaround on by default, then subsequently disabled if no CPUs are affected. Thanks, Mark diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index 8a7ff73..5370626 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -145,7 +145,6 @@ static inline void cpus_set_cap(unsigned int num) num, ARM64_NCAPS); } else { __set_bit(num, cpu_hwcaps); - static_branch_enable_cpuslocked(&cpu_hwcap_keys[num]); } } @@ -223,7 +222,7 @@ void update_cpu_capabilities(const struct arm64_cpu_capabilities *caps, void check_local_cpu_capabilities(void); void update_cpu_errata_workarounds(void); -void update_cpu_errata_workarounds_cpuslocked(void); +void update_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 57d60fa..2ed2a76 100644 --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -190,16 +190,9 @@ void verify_local_cpu_errata_workarounds(void) } } -void update_cpu_errata_workarounds_cpuslocked(void) -{ - update_cpu_capabilities(arm64_errata, "enabling workaround for"); -} - void update_cpu_errata_workarounds(void) { - get_online_cpus(); - update_cpu_errata_workarounds_cpuslocked(); - put_online_cpus(); + update_cpu_capabilities(arm64_errata, "enabling workaround for"); } void __init enable_errata_workarounds(void) diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 803afae..68ed74d 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -986,8 +986,16 @@ void update_cpu_capabilities(const struct arm64_cpu_capabilities *caps, */ void __init enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps) { - for (; caps->matches; caps++) - if (caps->enable && cpus_have_cap(caps->capability)) + for (; caps->matches; caps++) { + unsigned int num = caps->capability; + + if (!cpus_have_cap(num)) + continue; + + /* Ensure cpus_have_const_cap(num) works */ + static_branch_enable(&cpu_hwcap_keys[num]); + + if (caps->enable) { /* * Use stop_machine() as it schedules the work allowing * us to modify PSTATE, instead of on_each_cpu() which @@ -995,6 +1003,8 @@ void __init enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps) * we return. */ stop_machine(caps->enable, NULL, cpu_online_mask); + } + } } /* @@ -1086,7 +1096,7 @@ void check_local_cpu_capabilities(void) * advertised capabilities. */ if (!sys_caps_initialised) - update_cpu_errata_workarounds_cpuslocked(); + update_cpu_errata_workarounds(); else verify_local_cpu_capabilities(); } -- 1.9.1
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