linux-kernel - [PATCH v4 2/2] virtiofs: use GFP_NOFS when enqueuing request through kworker

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Message-Id: <20240831093750.1593871-3-houtao@huaweicloud.com>
Date: Sat, 31 Aug 2024 17:37:50 +0800
From: Hou Tao <houtao@...weicloud.com>
To: linux-fsdevel@...r.kernel.org
Cc: Miklos Szeredi <miklos@...redi.hu>,
	Vivek Goyal <vgoyal@...hat.com>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	Bernd Schubert <bernd.schubert@...tmail.fm>,
	"Michael S . Tsirkin" <mst@...hat.com>,
	Matthew Wilcox <willy@...radead.org>,
	Benjamin Coddington <bcodding@...hat.com>,
	Jingbo Xu <jefflexu@...ux.alibaba.com>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux.dev,
	houtao1@...wei.com
Subject: [PATCH v4 2/2] virtiofs: use GFP_NOFS when enqueuing request through kworker

From: Hou Tao <houtao1@...wei.com>

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@...wei.com>
---
 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) {
 			/*
-- 
2.29.2