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Tsirkin" Cc: Linus Torvalds , Linux Kernel Mailing List , "Kirill A . Shutemov" , Huang Ying , Jonathan Corbet , Peter Zijlstra , Thomas Gleixner , Thorsten Leemhuis , stable , linux-mm Subject: Re: [PATCH v2 1/3] mm/gup_benchmark: handle gup failures Message-Id: <20180409173821.889f0a2dd4385ee2428c16b8@linux-foundation.org> In-Reply-To: <20180408060935-mutt-send-email-mst@kernel.org> References: <1522962072-182137-1-git-send-email-mst@redhat.com> <1522962072-182137-3-git-send-email-mst@redhat.com> <20180408060935-mutt-send-email-mst@kernel.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-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: On Sun, 8 Apr 2018 06:12:13 +0300 "Michael S. Tsirkin" wrote: > On Sat, Apr 07, 2018 at 01:08:43PM -0700, Linus Torvalds wrote: > > On Thu, Apr 5, 2018 at 2:03 PM, Michael S. Tsirkin wrote: > > > > > > nr = get_user_pages_fast(addr, nr, gup->flags & 1, pages + i); > > > - i += nr; > > > + if (nr > 0) > > > + i += nr; > > > > Can we just make this robust while at it, and just make it > > > > if (nr <= 0) > > break; > > > > instead? Then it doesn't care about zero vs negative error, and > > wouldn't get stuck in an endless loop if it got zero. > > > > Linus > > I don't mind though it alredy breaks out on the next cycle: > > if (nr != gup->nr_pages_per_call) > break; > > the only issue is i getting corrupted when nr < 0; > It does help readability to have the thing bail out as soon as we see something go bad. This? --- a/mm/gup_benchmark.c~mm-gup_benchmark-handle-gup-failures-fix +++ a/mm/gup_benchmark.c @@ -41,8 +41,9 @@ static int __gup_benchmark_ioctl(unsigne } nr = get_user_pages_fast(addr, nr, gup->flags & 1, pages + i); - if (nr > 0) - i += nr; + if (nr <= 0) + break; + i += nr; } end_time = ktime_get(); _