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d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=mox7FaPJWIYIRuYrY0ZpJ9BmZbviHmr9/DMK0U0NTmQ=; b=qxuZuSL9RGfUkYD+IZNZNnQPcUYym1VEwBOPnHIlvec37PLigRVfI9yMwraEMPI5go TpoxhRP1epGuxbZS3Gj3W08ElBnTiYRURIAamv9cp6gwuj9EXvmiC0Y2GzFb6+7BA6Vp sO+Uoxi+Itxn6nW2mF8S5yVkwqJYGccVIWnltcJtpBd8KqP+b4y5uIDOWbl0sCt/IGAE FcqRHYT87qqzYl5/U54mFhgPi4f913n8kHq6YvquBwpjNd/ueFcVTzJ1kzK82M4d25yn 9pol7O/yEfh1GYrRbHMXpeWY6x/L4avhJPm8PC7aTuWvYfQeSishAdC0Fh1uzU5gcaz/ qP+A== X-Gm-Message-State: AOAM530Yii88wWxBedRm1z9WN2T/RGNsvy/kOmoW5c0rmBVM7YzJjxdM T7Ql3vAiLMXCEvmQaOjSWaNWxI84M2toc3CgDgw= X-Google-Smtp-Source: ABdhPJxvV+S94s7WbQ91OF8bg0Ot7QRgo1I2wb50ifHYaOAxLg/5ebTqDk4OVlKpP2lu6ovOroMq4ydD3Gt+r50G/VE= X-Received: by 2002:a05:651c:2c9:: with SMTP id f9mr4151065ljo.257.1600048245333; Sun, 13 Sep 2020 18:50:45 -0700 (PDT) MIME-Version: 1.0 References: <1600007555-11650-1-git-send-email-jrdr.linux@gmail.com> <20200913145520.GH6583@casper.infradead.org> In-Reply-To: <20200913145520.GH6583@casper.infradead.org> From: Souptick Joarder Date: Mon, 14 Sep 2020 07:20:34 +0530 Message-ID: Subject: Re: [PATCH] mm/gup.c: Handling ERR within unpin_user_pages() To: Matthew Wilcox Cc: Andrew Morton , Linux-MM , linux-kernel@vger.kernel.org, John Hubbard Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 4D6B816A047 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000005, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Sep 13, 2020 at 8:25 PM Matthew Wilcox wrote: > > On Sun, Sep 13, 2020 at 08:02:35PM +0530, Souptick Joarder wrote: > > It is possible that a buggy caller of unpin_user_pages() > > (specially in error handling path) may end up calling it with > > npages < 0 which is unnecessary. > > @@ -328,6 +328,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages) > > { > > unsigned long index; > > > > + if (WARN_ON_ONCE(npages < 0)) > > + return; > > But npages is unsigned long. So it can't be less than zero. Sorry, I missed it. Then, it means if npages is assigned with -ERRNO by caller, unpin_user_pages() may end up calling a big loop, which is unnecessary.