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Tue, 07 Apr 2020 18:40:21 -0700 (PDT) Received: from xz-x1.hitronhub.home ([2607:9880:19c0:32::3]) by smtp.gmail.com with ESMTPSA id x24sm6126607qth.80.2020.04.07.18.40.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Apr 2020 18:40:18 -0700 (PDT) From: Peter Xu To: linux-kernel@vger.kernel.org, Linus Torvalds , linux-mm@kvack.org Cc: Andrew Morton , peterx@redhat.com, syzbot+a8c70b7f3579fc0587dc@syzkaller.appspotmail.com Subject: [PATCH 2/2] mm/gup: Mark lock taken only after a successful retake Date: Tue, 7 Apr 2020 21:40:10 -0400 Message-Id: <20200408014010.80428-3-peterx@redhat.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200408014010.80428-1-peterx@redhat.com> References: <20200408014010.80428-1-peterx@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable 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: It's definitely incorrect to mark the lock as taken even if down_read_killable() failed. It's overlooked when we switched from down_read() to down_read_killable() because down_read() won't fail while down_read_killable() could. Reported-by: syzbot+a8c70b7f3579fc0587dc@syzkaller.appspotmail.com Fixes: 71335f37c5e8 ("mm/gup: allow to react to fatal signals") Signed-off-by: Peter Xu --- mm/gup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/gup.c b/mm/gup.c index da3e03185144..1f9a9b3a5869 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1328,7 +1328,6 @@ static __always_inline long __get_user_pages_locked(s= truct task_struct *tsk, =09=09if (fatal_signal_pending(current)) =09=09=09break; =20 -=09=09*locked =3D 1; =09=09ret =3D down_read_killable(&mm->mmap_sem); =09=09if (ret) { =09=09=09BUG_ON(ret > 0); @@ -1337,6 +1336,7 @@ static __always_inline long __get_user_pages_locked(s= truct task_struct *tsk, =09=09=09break; =09=09} =20 +=09=09*locked =3D 1; =09=09ret =3D __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED, =09=09=09=09 pages, NULL, locked); =09=09if (!*locked) { --=20 2.24.1