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[2003:cb:c735:f200:cb49:cb8f:88fc:9446]) by smtp.gmail.com with ESMTPSA id n24-20020a1c7218000000b003fefb94ccc9sm6966596wmc.11.2023.10.02.04.04.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Oct 2023 04:04:52 -0700 (PDT) Message-ID: <6161e8a8-64a4-c4ea-626d-daac45ccd836@redhat.com> Date: Mon, 2 Oct 2023 13:04:51 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH 3/4] mm/gup: make failure to pin an error if FOLL_NOWAIT not specified To: Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Catalin Marinas , Will Deacon , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland Cc: Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Adrian Hunter , Oleg Nesterov , Richard Cochran , Jason Gunthorpe , John Hubbard , Arnd Bergmann References: From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: A8BBD40012 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: z56h55dy4fe1x8zjo9yieku6917u4bkd X-HE-Tag: 1696244696-76082 X-HE-Meta: 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 M4FerCVL APlNG6Z6jtjnqN8omSFsVOKJzC0auDjFLs1DpMYVhR0B2f8GB5+Y+hCdeB1OgzSzMQb8HF4PKYKM1a8UzAgE9k2YT6T8GbMUnclTEbuZ9QaCB/3X2B4kzzAjUlOKC3pULGH9KDGxlyen1FKTnQqTgmB/wGkAP4YpciS7q1hdBeNPKlS/R5jppi5EDHsD20LMfXs696V5NaVCxZ2035zHAi8zdAtx7BO2kCLvI4MTMTqkGTtc/LNgX7ZTMmCzAzZ6VAGRKpBTOWimayHiCuKL1E67v74ryf19shHRk+wBBXsE41RQ1seQjUsoH2zC8fZVmpOIWj2aRTWY957EpHGXy5kCaXgW4RQ3bVTTVahxHx4znLQ7agf6xUGjoLJTc0wch3Nv2amYjeOzyxe6PzHcYqNdXuBzO9TGfghJcwn2mVKK/1ajh23Nh21z2hMWeaQipqR1HxuEODyz3Wcs= 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 01.10.23 18:00, Lorenzo Stoakes wrote: > There really should be no circumstances under which a non-FOLL_NOWAIT GUP > operation fails to return any pages, so make this an error. > > To catch the trivial case, simply exit early if nr_pages == 0. > > This brings __get_user_pages_locked() in line with the behaviour of its > nommu variant. > > Signed-off-by: Lorenzo Stoakes > --- > mm/gup.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/mm/gup.c b/mm/gup.c > index b21b33d1787e..fb2218d74ca5 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1471,6 +1471,9 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm, > long ret, pages_done; > bool must_unlock = false; > > + if (!nr_pages) > + return 0; > + Probably unlikely() is reasonable. I even wonder if WARN_ON_ONCE() would be appropriate, but likely there are weird callers that end up calling this with nr_pages==0 ... probably they should be identified and changed. Future work. > /* > * The internal caller expects GUP to manage the lock internally and the > * lock must be released when this returns. > @@ -1595,6 +1598,14 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm, > mmap_read_unlock(mm); > *locked = 0; > } > + > + /* > + * Failing to pin anything implies something has gone wrong except when > + * FOLL_NOWAIT is specified, so explicitly make this an error. > + */ > + if (pages_done == 0 && !(flags & FOLL_NOWAIT)) > + return -EFAULT; > + But who would be affected by that and why do we care about adding this check? This smells like a "if (WARN_ON_ONCE())", correct? -- Cheers, David / dhildenb