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Mon, 09 Nov 2026 06:08:42 -0800 (PST) Received: from gmail.com ([2a03:2880:24ff::]) by smtp.gmail.com with ESMTPSA id 00721157ae682-8b36b6320a5sm35777587b3.5.2026.11.09.06.08.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Nov 2026 06:08:41 -0800 (PST) Date: Mon, 9 Nov 2026 06:08:40 -0800 From: Breno Leitao To: John Ogness Cc: Petr Mladek , Sergey Senozhatsky , Steven Rostedt , Ryan Roberts , printk@lists.linux.dev, linux-kernel@vger.kernel.org, Greg Kroah-Hartman Subject: Re: [PATCH printk 3/6] printk: Evaluate flush policy in nbcon_allow_unsafe_takeover() Message-ID: References: <20261109123127.489676-1-john.ogness@linutronix.de> <20261109123127.489676-4-john.ogness@linutronix.de> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261109123127.489676-4-john.ogness@linutronix.de> On Mon, Nov 09, 2026 at 01:37:20PM +0106, John Ogness wrote: > @@ -1572,7 +1608,12 @@ static int __nbcon_atomic_flush_pending_con(struct console *con, enum pr_flush_r > ctxt->console = con; > ctxt->spinwait_max_us = 2000; > ctxt->prio = nbcon_get_default_prio(); > - ctxt->allow_unsafe_takeover = nbcon_allow_unsafe_takeover(); > + ctxt->allow_unsafe_takeover = nbcon_allow_unsafe_takeover(con, reason); Thanks for the series, I've tried it here, and I got: sysrq: Resetting ------------[ cut here ]------------ WARNING: kernel/printk/nbcon.c:561 at nbcon_context_try_acquire+0x72c/0x790, CPU#0: sh/212 Modules linked in: nbcon_hold(OE+) CPU: 0 UID: 0 PID: 212 Comm: sh Tainted: G OE 7.4.0-rc1-next-20261105upstream-00006-g4170adac69fb #1 PREEMPT(full) Hardware name: linux,dummy-virt (DT) pc : nbcon_context_try_acquire+0x72c/0x790 lr : nbcon_context_try_acquire+0x508/0x790 ... Call trace: nbcon_context_try_acquire+0x72c/0x790 (P) __nbcon_atomic_flush_pending_con+0x1c0/0x358 nbcon_atomic_flush_pending+0x224/0x390 printk_trigger_flush+0x50/0x1c8 emergency_restart+0x54/0x98 sysrq_handle_reboot+0x5c/0x88 __handle_sysrq+0x298/0x3c0 write_sysrq_trigger+0x178/0x1d0 proc_reg_write+0x148/0x270 vfs_write+0x1d4/0x7c8 ksys_write+0xbc/0x168 __arm64_sys_write+0x88/0xa8 invoke_syscall+0x74/0x188 do_el0_svc+0x108/0x190 el0_svc+0x60/0x1d8 el0t_64_sync_handler+0x68/0xe0 el0t_64_sync+0x198/0x1a0 That is coming from: 550 static int nbcon_context_try_acquire_hostile(struct nbcon_context *ctxt, 551 struct nbcon_state *cur) 552 { 553 unsigned int cpu = smp_processor_id(); 554 struct console *con = ctxt->console; 555 struct nbcon_state new; 556 557 if (!ctxt->allow_unsafe_takeover) 558 return -EPERM; 559 560 /* Ensure caller is allowed to perform unsafe hostile takeovers. */ 561 if (WARN_ON_ONCE(ctxt->prio != NBCON_PRIO_PANIC)) 562 return -EPERM; Thanks, --breno