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Tsirkin" Cc: Linus Torvalds , Al Viro , Linux Kernel Mailing List , stable , syzbot+6304bf97ef436580fede@syzkaller.appspotmail.com, linux-mm , "Kirill A. Shutemov" , Andrew Morton , Huang Ying , Jonathan Corbet , Peter Zijlstra , Thomas Gleixner , Thorsten Leemhuis Subject: Re: [PATCH] gup: return -EFAULT on access_ok failure Message-ID: <20180406123545.24953eb4@alans-desktop> In-Reply-To: <20180405211945-mutt-send-email-mst@kernel.org> References: <1522431382-4232-1-git-send-email-mst@redhat.com> <20180405045231-mutt-send-email-mst@kernel.org> <20180405171009-mutt-send-email-mst@kernel.org> <20180405211945-mutt-send-email-mst@kernel.org> Organization: Intel Corporation X-Mailer: Claws Mail 3.15.1-dirty (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: > so an error on the 1st page gets propagated to the caller, > and that get_user_pages_unlocked eventually calls __get_user_pages > so it does return an error sometimes. > > Would it be correct to apply the second part of the patch then > (pasted below for reference) or should get_user_pages_fast > and all its callers be changed to return 0 on error instead? 0 isn't an error. As SuS sees it (ie from the userspace end of the pile) returning the number you asked for means it worked returning a smaller number means it worked partially and that much was consumed (or in some cases more and the rest if so was lost - depends what you are reading/writing) returning 0 means you read nothing as you were at the end of file returning an error code means it broke, or you should try again (EAGAIN/EWOULDBLOCK) The ugly bit there is the try-again semantics needs to exactly match the attached poll() behaviour or you get busy loops. Alan