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b=UCZ68iJ+2TwxqdabJNKHBbq8jGZ/2EJdLAUuAH3h7VBEgYxI/n7kXeNv3eVD1Zz3P yvI8PZGs8KBq2Wakr6Q1C8l0bLhK848YNlHcAPZAInPOQjTPJqDdbNYT+xzk4K9krV aVLTx76+vTC1aHSADmIXR3n1vTndOO3XdMl4V6Nw= Date: Mon, 2 Mar 2026 12:43:05 -0800 From: Andrew Morton To: Alexey Suchkov Cc: dywoq.contact@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox , Joshua Hahn Subject: Re: [PATCH] [PATCH v2] mm: initialize 'seq' in gup_fast to remove -Wmaybe-uninitialized warning Message-Id: <20260302124305.6bb7f34228bfe07094de51ca@linux-foundation.org> In-Reply-To: <20260302193405.37961-1-dywoq.contact@gmail.com> References: <20260302191237.34375-1-dywoq.contact@gmail.com> <20260302193405.37961-1-dywoq.contact@gmail.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: yajawnsb9ncuxrs8uifzrfus9krddzdj X-Rspam-User: X-Rspamd-Queue-Id: 6418840003 X-Rspamd-Server: rspam12 X-HE-Tag: 1772484187-775235 X-HE-Meta: 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 fQ/E7zkS GPIt9rp1ugqx+rcG/VDipoXZ6tYtgRFlI/i03+j5S5UUvap7whpip+VYFgF0cv33xMAGy72d/pNTwT/DmRG3ghddjt46quy8vhjgDg1bfk78yf9FNwB9RN0o6NdO/KQHw1BFfda34Ht+UNlG4GNppQFEt7AlU+6wfakZ93sORkWFev/egJsBh+K4EV7elI42s27AWWxPWX8NsovjGXdsX/331xXrYDh24mpYRdbvwT9OadjsyzXKW9lqXEb/JJfkhwWw7owsXjyh7Lo5yPWNCMMqQAM6imJl4OCu/2dDcXp2CfnhaPCJ2NCtQkT0Sld8yf+htdMab31JHuJOXXs4tT1sHZjePM5rXw4pxwASZC2LDMZCvhTYQb/MZm5+JaaIIJdwsp9QNMLqDBnpW7X/vPgMV8JM8baRJcAZx Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 2 Mar 2026 22:34:05 +0300 Alexey Suchkov wrote: > The local variable 'seq' in gup_fast (mm/gup.c) was declared > without initialization, which can trigger: > > mm/gup.c:3165:20: warning: ‘seq’ may be used uninitialized [-Wmaybe-uninitialized] > > Initialize 'seq' to 0. This does not change behavior, since > read_seqcount_retry() always writes to it before use. > > ... > > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -3131,7 +3131,7 @@ static unsigned long gup_fast(unsigned long start, unsigned long end, > { > unsigned long flags; > int nr_pinned = 0; > - unsigned seq; > + unsigned int seq = 0; > > if (!IS_ENABLED(CONFIG_HAVE_GUP_FAST) || > !gup_fast_permitted(start, end)) stupid gcc. I liked uninitalized_var(), particularly for its self-documenting nature. Never agreed with Linus's hate on it. Thanks, I tweaked the changelog a bit: : The local variable 'seq' in gup_fast (mm/gup.c) was declared : without initialization, which with gcc-15.2.1 can trigger: : : mm/gup.c:3165:20: warning: `seq' may be used uninitialized [-Wmaybe-uninitialized] : : Work around this by initializing 'seq' to 0. This does not change : behavior, since read_seqcount_retry() always writes to it before use.