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Tue, 27 Oct 2026 08:02:36 -0700 (PDT) Received: from pathway.suse.cz ([176.114.240.130]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a35a5698f1sm269405355e9.8.2026.10.27.08.02.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Oct 2026 08:02:36 -0700 (PDT) Date: Tue, 27 Oct 2026 16:02:34 +0100 From: Petr Mladek To: Wang Wensheng Cc: rostedt@goodmis.org, john.ogness@linutronix.de, senozhatsky@chromium.org, d-tatianin@yandex-team.ru, linux-kernel@vger.kernel.org Subject: Re: [PATCH] printk_ringbuffer: Fix space_used() when blk_lpos->next overflows Message-ID: References: <20261004075755.363989-1-wsw9603@163.com> 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: <20261004075755.363989-1-wsw9603@163.com> On Sun 2026-10-04 15:57:55, Wang Wensheng wrote: > Since commit 67e1b0052f6b ("printk_ringbuffer: don't needlessly wrap data > blocks around") blk_lpos is treated as not wrapped when blk_lpos->next > overflows to the start of data_ring. We use the indices of blk_lpos->next > and blk_lpos->start to calculate the size of the data_block. This computes > zero minus a small positive value, resulting in underflow and an > unexpectedly large value. Simply using the original lpos with wrap-counts > solves the problem. > > Fixes: 67e1b0052f6b ("printk_ringbuffer: don't needlessly wrap data blocks around") > Signed-off-by: Wang Wensheng JFYI, the patch has been committed into printk/linux.git, branch for-7.4-fixups. Best Regards, Petr