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dkim=pass header.d=linutronix.de header.s=2020e header.b=gz7U0UH3; dmarc=pass (policy=none) header.from=linutronix.de; spf=pass (imf12.hostedemail.com: domain of john.ogness@linutronix.de designates 193.142.43.55 as permitted sender) smtp.mailfrom=john.ogness@linutronix.de ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1754494497; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=3IGF3vGHoaV5az/qlqBIi9OrCnbX/sgelHE61GcLMXw=; b=pKWCmyM0WbylQtpVgZbGe2CvSdfo2YOA2hiYvkyyRihRYTJydQyxxI39F4hUuyVlIfHuua nUWSeDcl36ChweV48IiKbUGvZ31SSe+GYS2CcV3wpe0OzhAb9zjbPknO8ozyFJoutvWDLl 8biCO39RT0rS0jgoVhiA6KJjMuCs0TU= From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1754494494; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=3IGF3vGHoaV5az/qlqBIi9OrCnbX/sgelHE61GcLMXw=; b=f5UiBCN4kJ1HFb25h6Vx7h06v5L5ZvrJzxTpOLbwmhrNc1MaPso/s6ShfglUvmMxI6TwN0 SW5LtbRIajAIeYh91s5H8GzyaxSk370RnKmxER8I7lxJB1Loq1N+t0dZjqXKzDf/m9sH0M GI2C8cc0V//XB+6BVOZ6oH3qfOJTte+z83pGI4N4SrwfUR9luIns9x2D6A4YC1Z1nmw4DN MSgQKzsofh/u51W427BMan5xO0hRuGZNy5ZJMIVorybIWZFgEDK+6+4nB01mu9I5O2LBQq pJjGuMHOG3cATRWPzhAj5ezzyUYkC9O1QB80VXAWCO/6VOoJmgT3M4V4NOx2yw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1754494494; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=3IGF3vGHoaV5az/qlqBIi9OrCnbX/sgelHE61GcLMXw=; b=gz7U0UH3TfuIQPgHoA1kb6pQvMSO5JbdTOEPwixJDow34ugYEJ3hxx8YvpBtdboIdvFU7h s0JaK3Ju7uvlS8CQ== To: Waiman Long , Andrew Morton , Gu Bowen Cc: Catalin Marinas , stable@vger.kernel.org, linux-mm@kvack.org, Lu Jialin , Breno Leitao Subject: Re: [PATCH] mm: Fix possible deadlock in console_trylock_spinning In-Reply-To: <5ca375cd-4a20-4807-b897-68b289626550@redhat.com> References: <20250730094914.566582-1-gubowen5@huawei.com> <20250801153303.cee42dcfc94c63fb5026bba0@linux-foundation.org> <5ca375cd-4a20-4807-b897-68b289626550@redhat.com> Date: Wed, 06 Aug 2025 17:40:53 +0206 Message-ID: <84h5yko44i.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: EFC154000F X-Stat-Signature: ph9ei9y3kqu1numr7u6ojy9rad7tnr9x X-Rspam-User: X-HE-Tag: 1754494496-679054 X-HE-Meta: U2FsdGVkX19Pb4xtXYQHNVtj4na0DlKlNFlqP9lsZ2xBnrNqY0E4MKGrg7wSMLcFtqWWW47vf6Gh1Ld3hDLUlyfzFRgPzKxKWew16gJKENNAwL37qfl/2FyTpZpT/Y3vNHwCS0V6KanGrAY8y6QvbE8tXBHCXfcm95u7prq+3+hH1hW7oSwXU01lDrDnhGGRANBI3Dvs0BCl8SKbFio9yJGLK5899FugJYbhbSuVDTfmTatK/IOxM/J9eLrV/Ek/afzE4+YTMbRQNhYPQ4LoiQlD7YaXffDtGmxkgHKEkQcitdcmVPAmwg9WV2EgbaG2uoQ8Gasi9CnlBMG/2E9ZUDycmR7ZwRQ/mc6ufq+gpKk/hLNzU0S98Ghw+XwHdj4p/IkQzgAo9/Tcq6i6KXZ8G3ChcxyOoDlALkMI/AaJdajHeBAWfF0vhUPZ2DE/g3AVGd+w2atpltsYXQPf/e78wwqwUDZczkEYIuHhHQSTow2D/ts9JQ6MVTH5xbQTZiMr7p8ppwbPXRqe1/rr3DWfc+yhKiwHgvYFrsaD3dnTmIu6SH9+wWIKo1J7Lecvcb22XTWDKsMQyzJYBPjkvDZsJhOaWYmtxP7mmKmXAeyhYzOvcs3SadmE1KCz6QfhzZ1OYLZ6PO8TBRth9pY9TKPOIqgoNfLPPIT30hO7quBg2MGsIuD/0DWXqChE8E/YQoyqdkGUr9+XuyTUsJPUEU4lm4xGz5a8gjPoIAoboTxLo5kS/8V3RauO33MJ0n6eIoIfljEm75cFKdlXPf2z12+AOAddrxnqZLZO1TIjFiE9pUJxs1uFkOmBapc+HJEuqdvZ/LQqabOsBMBvDibn1hH0doiMx8bpgjtsYZ7r0m+we2JBlLj44+KpnJUvszRNNGzYbSaWHb5BHzHSb/hiy+pGLzi8nGfXpW17dujZHDICxBTZ9TOqbOT3DCSTs/Z/j03RueLZxychvMFYh/EYKYo 1ncCfbuX AtCIu6obBFE2gMyG9IW6qqtPFjfToB1EsYyMY9kCi6yR6et0XdfAycGwJc3LTX8RATWYBraD6mRPoZg969npH12ZsUoSUCynBm7mlg/B0AeP08hOuv+h2fIvkBbmnmST245VnXEaVPmVZhlsXKWkMveHDYAIME3CU6xiWsk8f8OEnihb04H4Qz8CmiE89EFmrhxaSPY5twMZiGrOlVLAEXR1hZg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025-08-01, Waiman Long wrote: >>> kmemleak_scan_thread() invokes scan_block() which may invoke a nomal >>> printk() to print warning message. This can cause a deadlock in the >>> scenario reported below: >>> >>> CPU0 CPU1 >>> ---- ---- >>> lock(kmemleak_lock); >>> lock(&port->lock); >>> lock(kmemleak_lock); >>> lock(console_owner); >>> >>> To solve this problem, switch to printk_safe mode before printing warning >>> message, this will redirect all printk()-s to a special per-CPU buffer, >>> which will be flushed later from a safe context (irq work), and this >>> deadlock problem can be avoided. printk no longer works like this. There are no special per-CPU buffers. As correctly pointed out by Longman, the proper interface is printk_deferred_enter()/printk_deferred_exit(). With the deferred interface, the printk message is still immediately stored in the printk ringbuffer (which is lockless) and only the console printing itself is deferred. John Ogness