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Tsirkin" To: Hou Tao Cc: linux-fsdevel@vger.kernel.org, Miklos Szeredi , Vivek Goyal , Stefan Hajnoczi , linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, houtao1@huawei.com Subject: Re: [PATCH] virtiofs: limit the length of ITER_KVEC dio by max_nopage_rw Message-ID: <20240222144828-mutt-send-email-mst@kernel.org> References: <20240103105929.1902658-1-houtao@huaweicloud.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240103105929.1902658-1-houtao@huaweicloud.com> On Wed, Jan 03, 2024 at 06:59:29PM +0800, Hou Tao wrote: > From: Hou Tao > > When trying to insert a 10MB kernel module kept in a virtiofs with cache > disabled, the following warning was reported: > > ------------[ cut here ]------------ > WARNING: CPU: 2 PID: 439 at mm/page_alloc.c:4544 ...... > Modules linked in: > CPU: 2 PID: 439 Comm: insmod Not tainted 6.7.0-rc7+ #33 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), ...... > RIP: 0010:__alloc_pages+0x2c4/0x360 > ...... > Call Trace: > > ? __warn+0x8f/0x150 > ? __alloc_pages+0x2c4/0x360 > __kmalloc_large_node+0x86/0x160 > __kmalloc+0xcd/0x140 > virtio_fs_enqueue_req+0x240/0x6d0 > virtio_fs_wake_pending_and_unlock+0x7f/0x190 > queue_request_and_unlock+0x58/0x70 > fuse_simple_request+0x18b/0x2e0 > fuse_direct_io+0x58a/0x850 > fuse_file_read_iter+0xdb/0x130 > __kernel_read+0xf3/0x260 > kernel_read+0x45/0x60 > kernel_read_file+0x1ad/0x2b0 > init_module_from_file+0x6a/0xe0 > idempotent_init_module+0x179/0x230 > __x64_sys_finit_module+0x5d/0xb0 > do_syscall_64+0x36/0xb0 > entry_SYSCALL_64_after_hwframe+0x6e/0x76 > ...... > > ---[ end trace 0000000000000000 ]--- > > The warning happened as follow. In copy_args_to_argbuf(), virtiofs uses > kmalloc-ed memory as bound buffer for fuse args, but > fuse_get_user_pages() only limits the length of fuse arg by max_read or > max_write for IOV_KVEC io (e.g., kernel_read_file from finit_module()). > For virtiofs, max_read is UINT_MAX, so a big read request which is about > 10MB is passed to copy_args_to_argbuf(), kmalloc() is called in turn > with len=10MB, and triggers the warning in __alloc_pages(): > WARN_ON_ONCE_GFP(order > MAX_ORDER, gfp)). > > A feasible solution is to limit the value of max_read for virtiofs, so > the length passed to kmalloc() will be limited. However it will affects > the max read size for ITER_IOVEC io and the value of max_write also needs > limitation. So instead of limiting the values of max_read and max_write, > introducing max_nopage_rw to cap both the values of max_read and > max_write when the fuse dio read/write request is initiated from kernel. > > Considering that fuse read/write request from kernel is uncommon and to > decrease the demand for large contiguous pages, set max_nopage_rw as > 256KB instead of KMALLOC_MAX_SIZE - 4096 or similar. > > Fixes: a62a8ef9d97d ("virtio-fs: add virtiofs filesystem") > Signed-off-by: Hou Tao So what should I do with this patch? It includes fuse changes but of course I can merge too if no one wants to bother either way... > --- > fs/fuse/file.c | 12 +++++++++++- > fs/fuse/fuse_i.h | 3 +++ > fs/fuse/inode.c | 1 + > fs/fuse/virtio_fs.c | 6 ++++++ > 4 files changed, 21 insertions(+), 1 deletion(-) > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > index a660f1f21540..f1beb7c0b782 100644 > --- a/fs/fuse/file.c > +++ b/fs/fuse/file.c > @@ -1422,6 +1422,16 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii, > return ret < 0 ? ret : 0; > } > > +static size_t fuse_max_dio_rw_size(const struct fuse_conn *fc, > + const struct iov_iter *iter, int write) > +{ > + unsigned int nmax = write ? fc->max_write : fc->max_read; > + > + if (iov_iter_is_kvec(iter)) > + nmax = min(nmax, fc->max_nopage_rw); > + return nmax; > +} > + > ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter, > loff_t *ppos, int flags) > { > @@ -1432,7 +1442,7 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter, > struct inode *inode = mapping->host; > struct fuse_file *ff = file->private_data; > struct fuse_conn *fc = ff->fm->fc; > - size_t nmax = write ? fc->max_write : fc->max_read; > + size_t nmax = fuse_max_dio_rw_size(fc, iter, write); > loff_t pos = *ppos; > size_t count = iov_iter_count(iter); > pgoff_t idx_from = pos >> PAGE_SHIFT; > diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h > index 1df83eebda92..fc753cd34211 100644 > --- a/fs/fuse/fuse_i.h > +++ b/fs/fuse/fuse_i.h > @@ -594,6 +594,9 @@ struct fuse_conn { > /** Constrain ->max_pages to this value during feature negotiation */ > unsigned int max_pages_limit; > > + /** Maximum read/write size when there is no page in request */ > + unsigned int max_nopage_rw; > + > /** Input queue */ > struct fuse_iqueue iq; > > diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c > index 2a6d44f91729..4cbbcb4a4b71 100644 > --- a/fs/fuse/inode.c > +++ b/fs/fuse/inode.c > @@ -923,6 +923,7 @@ void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm, > fc->user_ns = get_user_ns(user_ns); > fc->max_pages = FUSE_DEFAULT_MAX_PAGES_PER_REQ; > fc->max_pages_limit = FUSE_MAX_MAX_PAGES; > + fc->max_nopage_rw = UINT_MAX; > > INIT_LIST_HEAD(&fc->mounts); > list_add(&fm->fc_entry, &fc->mounts); > diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c > index 5f1be1da92ce..3aac31d45198 100644 > --- a/fs/fuse/virtio_fs.c > +++ b/fs/fuse/virtio_fs.c > @@ -1452,6 +1452,12 @@ static int virtio_fs_get_tree(struct fs_context *fsc) > /* Tell FUSE to split requests that exceed the virtqueue's size */ > fc->max_pages_limit = min_t(unsigned int, fc->max_pages_limit, > virtqueue_size - FUSE_HEADER_OVERHEAD); > + /* copy_args_to_argbuf() uses kmalloc-ed memory as bounce buffer > + * for fuse args, so limit the total size of these args to prevent > + * the warning in __alloc_pages() and decrease the demand for large > + * contiguous pages. > + */ > + fc->max_nopage_rw = min(fc->max_nopage_rw, 256U << 10); > > fsc->s_fs_info = fm; > sb = sget_fc(fsc, virtio_fs_test_super, set_anon_super_fc); > -- > 2.29.2