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Tue, 8 Sep 2026 19:25:55 +0800 Message-ID: Date: Tue, 8 Sep 2026 19:25:54 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 09/19] arm64: smp: Defer RCU registration during secondary CPU bringup To: Will Deacon CC: , , Thomas Gleixner , Catalin Marinas , Borislav Petkov , Lorenzo Pieralisi , Mark Rutland , David Woodhouse , Peter Zijlstra , Marc Zyngier References: <20260907164024.17164-1-will@kernel.org> <20260907164024.17164-10-will@kernel.org> <45c37592-f05d-4b1c-812b-0cb38d1c3e24@huawei.com> From: Jinjie Ruan In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.109.254] X-ClientProxiedBy: kwepems200001.china.huawei.com (7.221.188.67) To kwepemk200008.china.huawei.com (7.202.194.74) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260908_122616_258287_FCD7AC30 X-CRM114-Status: GOOD ( 22.73 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 在 2026/9/8 18:19, Will Deacon 写道: > Hi Jinjie, > > On Tue, Sep 08, 2026 at 04:55:36PM +0800, Jinjie Ruan wrote: >> 在 2026/9/8 0:40, Will Deacon 写道: >>> Calling rcutree_report_cpu_starting() early during boot can lead to >>> livelocks with the generic CPU hotplug mechanism if the boot CPU blocks >>> on an RCU grace period while the CPU being onlined is spinning in >>> cpuhp_ap_sync_alive(). >>> >>> In preparation for enabling the generic CPU hotplug code on arm64, split >>> up the trace_hardirqs_off() call during secondary CPU bringup so that we >>> update lockdep early but defer the tracing updates until after >>> notify_cpu_starting() has registered the new CPU with RCU, allowing us >>> to drop the explicit call to rcutree_report_cpu_starting() entirely. >>> >>> Signed-off-by: Will Deacon >>> --- >>> arch/arm64/kernel/smp.c | 5 ++--- >>> include/linux/rcutree.h | 2 +- >>> 2 files changed, 3 insertions(+), 4 deletions(-) >>> >>> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c >>> index f4cabf9e19e6..ff68640d0c0b 100644 >>> --- a/arch/arm64/kernel/smp.c >>> +++ b/arch/arm64/kernel/smp.c >>> @@ -217,8 +217,7 @@ asmlinkage notrace void secondary_start_kernel(void) >>> if (system_uses_irq_prio_masking()) >>> init_gic_priority_masking(); >>> >>> - rcutree_report_cpu_starting(cpu); >>> - trace_hardirqs_off(); >> >> I think we need to handle the printk problem before this patch as we >> discussed earlier. >> >> Otherwise defer the rcutree_report_cpu_starting() will trigger a >> false-positive lockdep"suspicious RCU usage" splat during early lock >> acquisitions as commit ce3d31ad3cac ("arm64/smp: Move >> rcu_cpu_starting() earlier") pointed out. > > Sorry, I meant to mention this in the cover letter but forgot about it. > I'm not sure that ce3d31ad3cac ("arm64/smp: Move rcu_cpu_starting() > earlier") is still relevant with the latest printk/console/lockdep code. > I tried quite hard to trigger lockdep splats manually, but the only way > I could do it was by using the "%pS" specifier to print the name of a > symbol in a module, which would cause an RCU walk of the module symbols > in the kallsyms code! Manually calling WARN() or even rcu_read_lock() / > spin_lock() did _not_ trigger a splat. Hi Will, Add "dyndbg="+p"" in cmdline, CONFIG_DEBUG_LOCK_ALLOC=y, CONFIG_PROVE_RCU_LIST=y, we can reproduce the warning as below: I believe there is also a problem in the RISC-V code itself here as store_cpu_topology() is common for RISC-V. [ 0.335162] smp: Bringing up secondary CPUs ... [ 0.345495] [ 0.345513] ============================= [ 0.345523] WARNING: suspicious RCU usage [ 0.345621] 7.3.0-rc2-00010-g2311ba2cd56f #500 Tainted: G W [ 0.345637] ----------------------------- [ 0.345646] kernel/locking/lockdep.c:3845 RCU-list traversed in non-reader section!! [ 0.345659] [ 0.345659] other info that might help us debug this: [ 0.345659] [ 0.345680] [ 0.345680] RCU used illegally from offline CPU! [ 0.345680] rcu_scheduler_active = 1, debug_locks = 1 [ 0.345725] locks held by swapper/1/0: 0, last CPU#1 [ 0.345743] [ 0.345743] stack backtrace: [ 0.345834] CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Tainted: G W 7.3.0-rc2-00010-g2311ba2cd56f #500 PREEMPT(full) [ 0.345885] Tainted: [W]=WARN [ 0.346077] Call trace: [ 0.346102] show_stack+0x20/0x38 (C) [ 0.346153] dump_stack_lvl+0xc4/0x150 [ 0.346176] dump_stack+0x18/0x28 [ 0.346194] lockdep_rcu_suspicious+0x170/0x238 [ 0.346217] __lock_acquire+0xf08/0x1818 [ 0.346237] lock_acquire+0x1e0/0x450 [ 0.346256] _raw_spin_lock_irqsave+0x70/0xc0 [ 0.346277] down_trylock+0x20/0x60 [ 0.346293] __down_trylock_console_sem+0x4c/0x118 [ 0.346316] vprintk_emit+0x2d8/0x3f8 [ 0.346333] vprintk_default+0x40/0x58 [ 0.346350] vprintk+0x3c/0x80 [ 0.346366] _printk+0x64/0x98 [ 0.346386] __dynamic_pr_debug+0x90/0xd8 [ 0.346406] acpi_get_cache_info+0x140/0x1a0 [ 0.346430] init_cache_level+0xec/0x110 [ 0.346450] detect_cache_attributes+0x74/0x7c0 [ 0.346473] update_siblings_masks+0x30/0x300 [ 0.346495] store_cpu_topology+0x70/0xf0 [ 0.346515] secondary_start_kernel+0xe0/0x178 [ 0.346535] __secondary_switched+0xc0/0xc8 > > Since that's not something I think we should be doing this early, I > decided to leave the code as-is unless I have a way to trigger a lockdep > splat with the relatively simple prints we have on the early error paths. > > Will