From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1033887AbdD0J60 (ORCPT ); Thu, 27 Apr 2017 05:58:26 -0400 Received: from foss.arm.com ([217.140.101.70]:35764 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754414AbdD0J6O (ORCPT ); Thu, 27 Apr 2017 05:58:14 -0400 Date: Thu, 27 Apr 2017 10:57:44 +0100 From: Mark Rutland To: Sebastian Siewior Cc: Suzuki K Poulose , catalin.marinas@arm.com, will.deacon@arm.com, Peter Zijlstra , Thomas Gleixner , LKML , Ingo Molnar , Steven Rostedt , linux-arm-kernel@lists.infradead.org Subject: Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem Message-ID: <20170427095744.GB31337@leverpostej> References: <20170418170442.665445272@linutronix.de> <20170425161037.GA27156@leverpostej> <20170425172838.mr3kyccsdteyjso5@linutronix.de> <20170426085958.GC27156@leverpostej> <20170426103236.GI27156@leverpostej> <20170427082719.3wyru4bk67kdmflb@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170427082719.3wyru4bk67kdmflb@linutronix.de> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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(); + } } }