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Fri, 30 Oct 2026 00:58:26 -0700 (PDT) Received: from osman.mioffice.cn ([43.224.245.178]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1ac19c6b969sm4741054c88.14.2026.10.30.00.58.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 Oct 2026 00:58:25 -0700 (PDT) From: Zhan Xusheng To: gregkh@linuxfoundation.org Cc: jirislaby@kernel.org, dmitry.torokhov@gmail.com, mathieu.poirier@linaro.org, linux-serial@vger.kernel.org, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, zhanxusheng@xiaomi.com Subject: Re: [PATCH v4 1/2] tty: sysrq: don't expose a partially written reset_seq Date: Fri, 30 Oct 2026 15:58:20 +0800 Message-ID: <20261030075820.207049-1-zhanxusheng1024@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <2026103014-sketch-headed-2fd1@gregkh> References: <2026103014-sketch-headed-2fd1@gregkh> 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-Transfer-Encoding: 8bit Hi Greg, On Fri, Oct 30, 2026 at 08:02:30AM +0100, Greg KH wrote: > I still don't understand what the root problem is here, sorry. Each keyboard keeps its own copy of reset_seq. It rebuilds the copy on the first key press after the parameter changes, and it rebuilds it wrong in two ways. 1) It adds the new keys to the old copy instead of replacing it (2/2): echo 56,29,111 > /sys/module/sysrq/parameters/reset_seq # Alt+Ctrl+Del (press any key) echo 59,60 > /sys/module/sysrq/parameters/reset_seq # F1+F2 Now F1+F2 does nothing. Only holding all five keys resets. So setting reset_seq once works, but changing it later does not. 2) It can rebuild the copy while the write is half done (1/2). The write stores the keys one at a time, and the keyboard may read the list in between: echo 59,60 > reset_seq store 59 <- F1 pressed: keyboard reads "59" as the sequence store 60 On a keyboard that has not used a reset sequence before, or on any keyboard once 2/2 is applied, that F1 press completes the one-key sequence and reboots the machine. The window is microseconds; I only hit it with an added delay. If you want this fixed, I'll send a v5 with a much smaller 1/2, plain changelogs, and the Assisted-by: tag I should have added from the start. Otherwise please drop it. Thanks, Zhan Xusheng