virtiofs: use GFP_NOFS when enqueuing request through kworker

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.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index d220e28..f685278 100644 (file)
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -97,7 +97,8 @@ 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 },
@@ -575,6 +576,8 @@ 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);
@@ -585,7 +588,9 @@ 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);
@@ -686,7 +691,7 @@ 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;
@@ -700,7 +705,7 @@ 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;
 
@@ -1366,7 +1371,8 @@ 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];
@@ -1387,8 +1393,8 @@ 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;
@@ -1396,7 +1402,7 @@ 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;
 
@@ -1490,7 +1496,7 @@ static void virtio_fs_send_req(struct fuse_iqueue *fiq, struct fuse_req *req)
                 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) {
                        /*