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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id x8-20020a817c08000000b00589b653b7adsm2888815ywc.136.2023.09.18.16.31.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 Sep 2023 16:31:03 -0700 (PDT) Date: Mon, 18 Sep 2023 16:30:54 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Suren Baghdasaryan cc: akpm@linux-foundation.org, willy@infradead.org, hughd@google.com, shy828301@gmail.com, mhocko@suse.com, vbabka@suse.cz, syzkaller-bugs@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+b591856e0f0139f83023@syzkaller.appspotmail.com Subject: Re: [PATCH 1/1] mm: lock VMAs skipped by a failed queue_pages_range() In-Reply-To: <20230918211608.3580629-1-surenb@google.com> Message-ID: <512d487a-758c-6d9c-787c-4169117d20cf@google.com> References: <20230918211608.3580629-1-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: D5BB340014 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: mmwwt6enuaam6aorirteomzmriagsp7s X-HE-Tag: 1695079865-268828 X-HE-Meta: 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 L2oUvP4t uPoe3WEj7kQdlvzpvcQO9SHcF7MbEt2nU3es4ABNJXPV6vayG7bBPdgU9KVk13Y5LsMnkuz40pW5SnAvgOhnhm3vOiiSf/wy0UXDjbWQ2/h3HSrskevt7e1PY3id/WzT9O7D5kcURVvyFgAYXR8SSo3fMLpEs/IOE0HPehdV6ENUyN2WnsJ6vA98YbZWgf2Bh8yY00BxykRHtDoW1LHZcO5CRGeV+YDACCZr2unNKVfJvU9OIt57ABaV+L8dE2xLs+PtcfWuCFDea0hsaM1lyqsrERr+VuqedhzBfIJfEX+GTmtRnN2HlrysAYn95PBLt2shpE95B7b9V5xZ56MReYDXhNSHTAyelyfKZlqjLjHW5dvKb+TEFoSE144JUl2BWQZ/bpnp90Z9hMrBSShJI/zWf0v+EEuq8zl1AbkEF6empuXYSs1R9CANs4avFbpks8AddijWVbAoC+kqrx1rEnoNm+Amy85gdRtbp/K+qfCsDNIFOMcceWUj8WPC6tE23WE8CvB/egjh3h54fyzlGTw2KDKR3jHynpo+JCCMgVD9eMiWmpYn8pahN6JPoB/Sk36GYHyEAqPwt1bvlt9sYIG/98oQoBSRjk1f9/AVuj7rBxboKtaGzhVzO9T33G0vEPdnS 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, 18 Sep 2023, Suren Baghdasaryan wrote: > When queue_pages_range() encounters an unmovable page, it terminates > its page walk. This walk, among other things, locks the VMAs in the range. > This termination might result in some VMAs being left unlock after > queue_pages_range() completes. Since do_mbind() continues to operate on > these VMAs despite the failure from queue_pages_range(), it will encounter > an unlocked VMA. > This mbind() behavior has been modified several times before and might > need some changes to either finish the page walk even in the presence > of unmovable pages or to error out immediately after the failure to > queue_pages_range(). However that requires more discussions, so to > fix the immediate issue, explicitly lock the VMAs in the range if > queue_pages_range() failed. The added condition does not save much > but is added for documentation purposes to understand when this extra > locking is needed. > > Fixes: 49b0638502da ("mm: enable page walking API to lock vmas during the walk") > Reported-by: syzbot+b591856e0f0139f83023@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/all/000000000000f392a60604a65085@google.com/ > Signed-off-by: Suren Baghdasaryan Acked-by: Hugh Dickins > --- > mm/mempolicy.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 42b5567e3773..cbc584e9b6ca 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -1342,6 +1342,9 @@ static long do_mbind(unsigned long start, unsigned long len, > vma_iter_init(&vmi, mm, start); > prev = vma_prev(&vmi); > for_each_vma_range(vmi, vma, end) { > + /* If queue_pages_range failed then not all VMAs might be locked */ > + if (ret) > + vma_start_write(vma); > err = mbind_range(&vmi, vma, &prev, start, end, new); > if (err) > break; > -- > 2.42.0.459.ge4e396fd5e-goog