On 8/31/24 5:37 PM, Hou Tao wrote:
> From: Hou Tao <houtao1@xxxxxxxxxx>
>
> When invoking virtio_fs_enqueue_req() through kworker, both the
> allocation of the sg array and the bounce buffer still use GFP_ATOMIC.
> Considering the size of the sg array may be greater than PAGE_SIZE, use
> GFP_NOFS instead of GFP_ATOMIC to lower the possibility of memory
> allocation failure and to avoid unnecessarily depleting the atomic
> reserves. GFP_NOFS is not passed to virtio_fs_enqueue_req() directly,
> GFP_KERNEL and memalloc_nofs_{save|restore} helpers are used instead.
>
> It may seem OK to pass GFP_NOFS to virtio_fs_enqueue_req() as well when
> queuing the request for the first time, but this is not the case. The
> reason is that fuse_request_queue_background() may call
> ->queue_request_and_unlock() while holding fc->bg_lock, which is a
> spin-lock. Therefore, still use GFP_ATOMIC for it.
Actually, .wake_pending_and_unlock() is called under fiq->lock and
GFP_ATOMIC is requisite.
>
> Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
> ---
> fs/fuse/virtio_fs.c | 24 +++++++++++++++---------
> 1 file changed, 15 insertions(+), 9 deletions(-)
>
> diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
> index 43d66ab5e891..9bc48b3ca384 100644
> --- a/fs/fuse/virtio_fs.c
> +++ b/fs/fuse/virtio_fs.c
> @@ -95,7 +95,8 @@ struct virtio_fs_req_work {
> };
>
> static int virtio_fs_enqueue_req(struct virtio_fs_vq *fsvq,
> - struct fuse_req *req, bool in_flight);
> + struct fuse_req *req, bool in_flight,
> + gfp_t gfp);
>
> static const struct constant_table dax_param_enums[] = {
> {"always", FUSE_DAX_ALWAYS },
> @@ -439,6 +440,8 @@ static void virtio_fs_request_dispatch_work(struct work_struct *work)
>
> /* Dispatch pending requests */
> while (1) {
> + unsigned int flags;
> +
> spin_lock(&fsvq->lock);
> req = list_first_entry_or_null(&fsvq->queued_reqs,
> struct fuse_req, list);
> @@ -449,7 +452,9 @@ static void virtio_fs_request_dispatch_work(struct work_struct *work)
> list_del_init(&req->list);
> spin_unlock(&fsvq->lock);
>
> - ret = virtio_fs_enqueue_req(fsvq, req, true);
> + flags = memalloc_nofs_save();
> + ret = virtio_fs_enqueue_req(fsvq, req, true, GFP_KERNEL);
> + memalloc_nofs_restore(flags);
> if (ret < 0) {
> if (ret == -ENOSPC) {
> spin_lock(&fsvq->lock);
> @@ -550,7 +555,7 @@ static void virtio_fs_hiprio_dispatch_work(struct work_struct *work)
> }
>
> /* Allocate and copy args into req->argbuf */
> -static int copy_args_to_argbuf(struct fuse_req *req)
> +static int copy_args_to_argbuf(struct fuse_req *req, gfp_t gfp)
> {
> struct fuse_args *args = req->args;
> unsigned int offset = 0;
> @@ -564,7 +569,7 @@ static int copy_args_to_argbuf(struct fuse_req *req)
> len = fuse_len_args(num_in, (struct fuse_arg *) args->in_args) +
> fuse_len_args(num_out, args->out_args);
>
> - req->argbuf = kmalloc(len, GFP_ATOMIC);
> + req->argbuf = kmalloc(len, gfp);
> if (!req->argbuf)
> return -ENOMEM;
>
> @@ -1239,7 +1244,8 @@ static unsigned int sg_init_fuse_args(struct scatterlist *sg,
>
> /* Add a request to a virtqueue and kick the device */
> static int virtio_fs_enqueue_req(struct virtio_fs_vq *fsvq,
> - struct fuse_req *req, bool in_flight)
> + struct fuse_req *req, bool in_flight,
> + gfp_t gfp)
> {
> /* requests need at least 4 elements */
> struct scatterlist *stack_sgs[6];
> @@ -1260,8 +1266,8 @@ static int virtio_fs_enqueue_req(struct virtio_fs_vq *fsvq,
> /* Does the sglist fit on the stack? */
> total_sgs = sg_count_fuse_req(req);
> if (total_sgs > ARRAY_SIZE(stack_sgs)) {
> - sgs = kmalloc_array(total_sgs, sizeof(sgs[0]), GFP_ATOMIC);
> - sg = kmalloc_array(total_sgs, sizeof(sg[0]), GFP_ATOMIC);
> + sgs = kmalloc_array(total_sgs, sizeof(sgs[0]), gfp);
> + sg = kmalloc_array(total_sgs, sizeof(sg[0]), gfp);
> if (!sgs || !sg) {
> ret = -ENOMEM;
> goto out;
> @@ -1269,7 +1275,7 @@ static int virtio_fs_enqueue_req(struct virtio_fs_vq *fsvq,
> }
>
> /* Use a bounce buffer since stack args cannot be mapped */
> - ret = copy_args_to_argbuf(req);
> + ret = copy_args_to_argbuf(req, gfp);
> if (ret < 0)
> goto out;
>
> @@ -1367,7 +1373,7 @@ __releases(fiq->lock)
> queue_id);
>
> fsvq = &fs->vqs[queue_id];
> - ret = virtio_fs_enqueue_req(fsvq, req, false);
> + ret = virtio_fs_enqueue_req(fsvq, req, false, GFP_ATOMIC);
> if (ret < 0) {
> if (ret == -ENOSPC) {
> /*
LGTM.
Reviewed-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
--
Thanks,
Jingbo
