Messages in this thread | | | Subject | Re: [PATCHv3] arm64/cpufeature: don't use mutex in bringup path | From | Suzuki K Poulose <> | Date | Fri, 12 May 2017 13:03:49 +0100 |
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On 12/05/17 11:15, Mark Rutland wrote: > 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. The poking of static keys is deferred > until enable_cpu_capabilities(), which runs in a suitable context on the > boot CPU. To account for the static keys being set later, > cpus_have_const_cap() is updated to use another static key to check > whether the const cap keys have been initialised, falling back to the > caps bitmap until this is the case. > > This means that users of cpus_have_const_cap() gain should only gain a > single additional NOP in the fast path once the const caps are > initialised, but should always see the current cap value. > > The hyp code should never dereference the caps array, since the caps are > initialized before we run the module initcall to initialise hyp. A check > is added to the hyp init code to docuemnt this requirement. > > This rework means that we can remove the *_cpuslocked() helpers added in > commit d54bb72551b999dd ("arm64/cpufeature: Use > static_branch_enable_cpuslocked()"). > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Christoffer Dall <christoffer.dall@linaro.org> > Cc: Marc Zyniger <marc.zyngier@arm.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Sebastian Sewior <bigeasy@linutronix.de> > Cc: Suzuki Poulose <suzuki.poulose@arm.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Will Deacon <will.deacon@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
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