Re: [PATCH v13 4/7] arm64: mte: Enable TCO in functions that can read beyond buffer limits
From: Vincenzo Frascino <vincenzo.frascino@arm.com>
Date: 2021-02-22 12:05:34
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On 2/12/21 5:21 PM, Catalin Marinas wrote:
quoted
+ + /* + * This function is called on each active smp core at boot + * time, hence we do not need to take cpu_hotplug_lock again. + */ + static_branch_enable_cpuslocked(&mte_async_mode); }Sorry, I missed the cpuslocked aspect before. Is there any reason you need to use this API here? I suggested to add it to the mte_enable_kernel_sync() because kasan may at some point do this dynamically at run-time, so the boot-time argument doesn't hold. But it's also incorrect as this function will be called for hot-plugged CPUs as well after boot. The only reason for static_branch_*_cpuslocked() is if it's called from a region that already invoked cpus_read_lock() which I don't think is the case here.
I agree with your analysis on why static_branch_*_cpuslocked() is needed, in fact cpus_read_lock() takes cpu_hotplug_lock as per comment on top of the line of code. If I try to take that lock when enabling the secondary cores I end up in the situation below: [ 0.283402] smp: Bringing up secondary CPUs ... .... [ 5.890963] Call trace: [ 5.891050] dump_backtrace+0x0/0x19c [ 5.891212] show_stack+0x18/0x70 [ 5.891373] dump_stack+0xd0/0x12c [ 5.891531] dequeue_task_idle+0x28/0x40 [ 5.891686] __schedule+0x45c/0x6c0 [ 5.891851] schedule+0x70/0x104 [ 5.892010] percpu_rwsem_wait+0xe8/0x104 [ 5.892174] __percpu_down_read+0x5c/0x90 [ 5.892332] percpu_down_read.constprop.0+0xbc/0xd4 [ 5.892497] cpus_read_lock+0x10/0x1c [ 5.892660] static_key_enable+0x18/0x3c [ 5.892823] mte_enable_kernel_async+0x40/0x70 [ 5.892988] kasan_init_hw_tags_cpu+0x50/0x60 [ 5.893144] cpu_enable_mte+0x24/0x70 [ 5.893304] verify_local_cpu_caps+0x58/0x120 [ 5.893465] check_local_cpu_capabilities+0x18/0x1f0 [ 5.893626] secondary_start_kernel+0xe0/0x190 [ 5.893790] 0x0 [ 5.893975] bad: scheduling from the idle thread! [ 5.894065] CPU: 1 PID: 0 Comm: swapper/1 Tainted: G W 5.11.0-rc7-10587-g22cd50bcfcf-dirty #6 and the kernel panics. Note: there is a look of msg drop in between enabling the secondary and the first clean stack trace. -- Regards, Vincenzo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel