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Mon, 23 Sep 2024 14:56:06 -0700 (PDT) Message-ID: <0f6afef57196cb308aa90be5b06a64793aa24682.camel@gmail.com> Subject: Re: [PATCH v2 19/25] netfs: Speed up buffered reading From: Eduard Zingerman To: Manu Bretelle , dhowells@redhat.com Cc: asmadeus@codewreck.org, ceph-devel@vger.kernel.org, christian@brauner.io, ericvh@kernel.org, hsiangkao@linux.alibaba.com, idryomov@gmail.com, jlayton@kernel.org, linux-afs@lists.infradead.org, linux-cifs@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-nfs@vger.kernel.org, marc.dionne@auristor.com, netdev@vger.kernel.org, netfs@lists.linux.dev, pc@manguebit.com, smfrench@gmail.com, sprasad@microsoft.com, tom@talpey.com, v9fs@lists.linux.dev, willy@infradead.org Date: Mon, 23 Sep 2024 14:56:01 -0700 In-Reply-To: <670794146059f85a30efd7cf9d6650375d987077.camel@gmail.com> References: <20240814203850.2240469-20-dhowells@redhat.com> <20240923183432.1876750-1-chantr4@gmail.com> <670794146059f85a30efd7cf9d6650375d987077.camel@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.52.4 (3.52.4-1.fc40) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2024-09-23 at 11:43 -0700, Eduard Zingerman wrote: > On Mon, 2024-09-23 at 11:34 -0700, Manu Bretelle wrote: >=20 > [...] >=20 > > The qemu command invoked by vmtest is: > >=20 > > qemu-system-x86_64 "-nodefaults" "-display" "none" "-serial" "mon:stdio= " \ > > "-enable-kvm" "-cpu" "host" "-qmp" "unix:/tmp/qmp-971717.sock,server= =3Don,wait=3Doff" \ > > "-chardev" "socket,path=3D/tmp/qga-888301.sock,server=3Don,wait=3Doff= ,id=3Dqga0" \ > > "-device" "virtio-serial" \ > > "-device" "virtserialport,chardev=3Dqga0,name=3Dorg.qemu.guest_agent.= 0" \ > > "--device" "virtio-serial" \ > > "-chardev" "socket,path=3D/tmp/cmdout-508724.sock,server=3Don,wait=3D= off,id=3Dcmdout" \ > > "--device" "virtserialport,chardev=3Dcmdout,name=3Dorg.qemu.virtio_se= rial.0" \ > > "-virtfs" "local,id=3Droot,path=3D/,mount_tag=3D/dev/root,security_mo= del=3Dnone,multidevs=3Dremap" \ > > "-kernel" "/data/users/chantra/linux/arch/x86/boot/bzImage" \ > > "-no-reboot" "-append" "rootfstype=3D9p rootflags=3Dtrans=3Dvirtio,ca= che=3Dmmap,msize=3D1048576 rw earlyprintk=3Dserial,0,115200 printk.devkmsg= =3Don console=3D0,115200 loglevel=3D7 raid=3Dnoautodetect init=3D/tmp/vmtes= t-init4PdCA.sh panic=3D-1" \ > > "-virtfs" "local,id=3Dshared,path=3D/data/users/chantra/linux,mount_t= ag=3Dvmtest-shared,security_model=3Dnone,multidevs=3Dremap" \ > > "-smp" "2" "-m" "4G" >=20 > fwiw: removing "cache=3Dmmap" from "rootflags" allows VM to boot and run = tests. >=20 A few more details: - error could be reproduced with KASAN enabled, log after scripts/decode_stacktrace.sh post-processing is in [1]; (KASAN reports use-after-free followed by null-ptr-deref); - null-ptr-deref is triggered by access to page->pcp_list.next when list_del() is called from page_alloc.c:__rmqueue_pcplist(), e.g. the following warning is triggered if added: --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2990,6 +2990,7 @@ struct page *__rmqueue_pcplist(struct zone *zone, u= nsigned int order, } =20 page =3D list_first_entry(list, struct page, pcp_list); + WARN_ONCE(!page->pcp_list.next, "!!!!! page->pcp_list.nex= t is NULL\n"); list_del(&page->pcp_list); pcp->count -=3D 1 << order; } while (check_new_pages(page, order)); - config used for testing is [2]; - kernel used for testing is [3]; [1] https://gist.github.com/eddyz87/e638d67454558508451331754f946f41 [2] https://gist.github.com/eddyz87/f2c9c267db20ee53a6eb350aba0d2182 [3] de5cb0dcb74c ("Merge branch 'address-masking'") https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git