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s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=t1FP4AWnie2gjJ2+aQoHhQuSZMsBtLy6T/hgMEanh9c=; b=K27kY874PoNNYWfRsBMysIP/LUkUi6N6z3gr2HWMs2eHTvXrkAanOqXf0XMpZKQ1Bs MlIoo19+UlTkW0rQH5n2Jn8zSqGrfsIgZ8AqQ5QZ+PYj4ykjGoMo/aPODnuv+DuiPRoQ DTmktCCcSZxoPrluwLJsxHRtl2C68NVG65gNHfK/yNM0RJT9MBOFl6ZgGEhaJ7PJTwEu EwJpCbc5fbbvk0Rn1pviljdYidyC6vxcVsvElZoB2tJNCPT3SpAnPIc1BECDDStw1DLn m/n+SvR9iBmdlozMoBnFp+oLUj0Yz2TdZa+Rws2Hud+A+lqBd5WYbpUjzNyX9bud2wjF nkwg== X-Gm-Message-State: AOAM532cpvQv4/L6hISD8o55cLJSWgGqqrbjNmkv6F3U5hQ6L9pl8wWi 8dXexlvDBtWBtlOyXJdgYGpsM90vgChOEofQ/Hs= X-Google-Smtp-Source: ABdhPJzpoL5GFI54NoyZ0KduFMFXvrdhGSfG5CRRJrvremcnlvt9gygB2S/03+RRhwenrupXwRp6m0AcAKcVUKrnXCA= X-Received: by 2002:a19:c801:: with SMTP id y1mr4642218lff.217.1600116765367; Mon, 14 Sep 2020 13:52:45 -0700 (PDT) MIME-Version: 1.0 References: <1600007555-11650-1-git-send-email-jrdr.linux@gmail.com> <20200913145520.GH6583@casper.infradead.org> <20200914140814.GE1221970@ziepe.ca> In-Reply-To: <20200914140814.GE1221970@ziepe.ca> From: Souptick Joarder Date: Tue, 15 Sep 2020 02:22:33 +0530 Message-ID: Subject: Re: [PATCH] mm/gup.c: Handling ERR within unpin_user_pages() To: Jason Gunthorpe Cc: Matthew Wilcox , Andrew Morton , Linux-MM , linux-kernel@vger.kernel.org, John Hubbard Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 529868008871 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 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: On Mon, Sep 14, 2020 at 7:38 PM Jason Gunthorpe wrote: > > On Mon, Sep 14, 2020 at 07:20:34AM +0530, Souptick Joarder wrote: > > 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. > > How will a caller allocate memory of the right size and still manage > to call with the wrong npages? Do you have an example of a broken caller? These are two broken callers which might end up calling unpin_user_pages() with -ERRNO. drivers/rapidio/devices/rio_mport_cdev.c#L952 drivers/misc/mic/scif/scif_rma.c#L1399 They both are in error handling paths, so might not have any serious impact. But theoretically possible.