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Mon, 02 Mar 2020 08:38:54 -0500 X-MC-Unique: F6dJcXFcOz2fv8P7oQrtFA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6878C8AB9E0; Mon, 2 Mar 2020 13:38:53 +0000 (UTC) Received: from localhost.localdomain (vpn2-54-46.bne.redhat.com [10.64.54.46]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 208449CA3; Mon, 2 Mar 2020 13:38:50 +0000 (UTC) Subject: Re: [PATCH] arm64/kernel: Simplify __cpu_up() by bailing out early To: Mark Rutland References: <20200302020340.119588-1-gshan@redhat.com> <20200302122135.GB56497@lakrids.cambridge.arm.com> From: Gavin Shan Message-ID: Date: Tue, 3 Mar 2020 00:38:48 +1100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: <20200302122135.GB56497@lakrids.cambridge.arm.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200302_053858_827218_97BA602D X-CRM114-Status: GOOD ( 27.46 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Gavin Shan Cc: catalin.marinas@arm.com, linux-kernel@vger.kernel.org, shan.gavin@gmail.com, maz@kernel.org, will@kernel.org, linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 3/2/20 11:21 PM, Mark Rutland wrote: > On Mon, Mar 02, 2020 at 01:03:40PM +1100, Gavin Shan wrote: >> The function __cpu_up() is invoked to bring up the target CPU through >> the backend, PSCI for example. The nested if statements won't be needed >> if we bail out early on the following two conditions where the status >> won't be checked. The code looks simplified in that case. >> >> * Error returned from the backend (e.g. PSCI) >> * The target CPU has been marked as onlined >> >> Signed-off-by: Gavin Shan > > FWIW, this looks like a nice cleanup to me: > > Reviewed-by: Mark Rutland > > While this patch leaves secondary_data.{task,stack} stale on a > successful onlining, that was already the case for a timeout, and should > be fine (since the next attempt at onlining will configure those before > poking the CPU). > > Thanks, > Mark. > Thanks, Mark. Yeah, it should be fine as you said. There are something else, which might be not relevant. @secondary_data could be accessed by multiple CPUs in parallel. For example, the master CPU boots CPU#1 and timeouts to wait it to be online in 5 seconds. CPU#1 isn't necessarily stuck in somewhere. After that, CPU#2 is brought up and might be accessing @secondary_data. At this point, CPU#1 can come back to access it either. However, @secondary_data isn't valid for CPU#1 anymore. I was thinking of something to improve the situation, but not sure if it makes any sense to do so. There are several options: (1) Make @secondary_data per-cpu variable, which looks a nature way to go. (2) To shutdown the CPU on timeout. The shutdown request can be failed to be served in theory, but it seems still an improvement. Thanks, Gavin >> --- >> arch/arm64/kernel/smp.c | 79 +++++++++++++++++++---------------------- >> 1 file changed, 37 insertions(+), 42 deletions(-) >> >> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c >> index d4ed9a19d8fe..2a9d8f39dc58 100644 >> --- a/arch/arm64/kernel/smp.c >> +++ b/arch/arm64/kernel/smp.c >> @@ -115,60 +115,55 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle) >> update_cpu_boot_status(CPU_MMU_OFF); >> __flush_dcache_area(&secondary_data, sizeof(secondary_data)); >> >> - /* >> - * Now bring the CPU into our world. >> - */ >> + /* Now bring the CPU into our world */ >> ret = boot_secondary(cpu, idle); >> - if (ret == 0) { >> - /* >> - * CPU was successfully started, wait for it to come online or >> - * time out. >> - */ >> - wait_for_completion_timeout(&cpu_running, >> - msecs_to_jiffies(5000)); >> - >> - if (!cpu_online(cpu)) { >> - pr_crit("CPU%u: failed to come online\n", cpu); >> - ret = -EIO; >> - } >> - } else { >> + if (ret) { >> pr_err("CPU%u: failed to boot: %d\n", cpu, ret); >> return ret; >> } >> >> + /* >> + * CPU was successfully started, wait for it to come online or >> + * time out. >> + */ >> + wait_for_completion_timeout(&cpu_running, >> + msecs_to_jiffies(5000)); >> + if (cpu_online(cpu)) >> + return 0; >> + >> + pr_crit("CPU%u: failed to come online\n", cpu); >> secondary_data.task = NULL; >> secondary_data.stack = NULL; >> __flush_dcache_area(&secondary_data, sizeof(secondary_data)); >> status = READ_ONCE(secondary_data.status); >> - if (ret && status) { >> - >> - if (status == CPU_MMU_OFF) >> - status = READ_ONCE(__early_cpu_boot_status); >> + if (status == CPU_MMU_OFF) >> + status = READ_ONCE(__early_cpu_boot_status); >> >> - switch (status & CPU_BOOT_STATUS_MASK) { >> - default: >> - pr_err("CPU%u: failed in unknown state : 0x%lx\n", >> - cpu, status); >> - cpus_stuck_in_kernel++; >> - break; >> - case CPU_KILL_ME: >> - if (!op_cpu_kill(cpu)) { >> - pr_crit("CPU%u: died during early boot\n", cpu); >> - break; >> - } >> - pr_crit("CPU%u: may not have shut down cleanly\n", cpu); >> - /* Fall through */ >> - case CPU_STUCK_IN_KERNEL: >> - pr_crit("CPU%u: is stuck in kernel\n", cpu); >> - if (status & CPU_STUCK_REASON_52_BIT_VA) >> - pr_crit("CPU%u: does not support 52-bit VAs\n", cpu); >> - if (status & CPU_STUCK_REASON_NO_GRAN) >> - pr_crit("CPU%u: does not support %luK granule \n", cpu, PAGE_SIZE / SZ_1K); >> - cpus_stuck_in_kernel++; >> + switch (status & CPU_BOOT_STATUS_MASK) { >> + default: >> + pr_err("CPU%u: failed in unknown state : 0x%lx\n", >> + cpu, status); >> + cpus_stuck_in_kernel++; >> + break; >> + case CPU_KILL_ME: >> + if (!op_cpu_kill(cpu)) { >> + pr_crit("CPU%u: died during early boot\n", cpu); >> break; >> - case CPU_PANIC_KERNEL: >> - panic("CPU%u detected unsupported configuration\n", cpu); >> } >> + pr_crit("CPU%u: may not have shut down cleanly\n", cpu); >> + /* Fall through */ >> + case CPU_STUCK_IN_KERNEL: >> + pr_crit("CPU%u: is stuck in kernel\n", cpu); >> + if (status & CPU_STUCK_REASON_52_BIT_VA) >> + pr_crit("CPU%u: does not support 52-bit VAs\n", cpu); >> + if (status & CPU_STUCK_REASON_NO_GRAN) { >> + pr_crit("CPU%u: does not support %luK granule\n", >> + cpu, PAGE_SIZE / SZ_1K); >> + } >> + cpus_stuck_in_kernel++; >> + break; >> + case CPU_PANIC_KERNEL: >> + panic("CPU%u detected unsupported configuration\n", cpu); >> } >> >> return ret; >> -- >> 2.23.0 >> > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel