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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <5769af42-e4dd-4535-9432-f149b8c17af5@linux.alibaba.com>
Date: Tue, 3 Sep 2024 17:34:01 +0800
From: Jingbo Xu <jefflexu@...ux.alibaba.com>
To: Hou Tao <houtao@...weicloud.com>, 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>,
 linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev,
 houtao1@...wei.com
Subject: Re: [PATCH v4 2/2] virtiofs: use GFP_NOFS when enqueuing request
 through kworker



On 8/31/24 5:37 PM, Hou Tao wrote:
> 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.

Actually, .wake_pending_and_unlock() is called under fiq->lock and
GFP_ATOMIC is requisite.


> 
> 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) {
>  			/*

LGTM.

Reviewed-by: Jingbo Xu <jefflexu@...ux.alibaba.com>



-- 
Thanks,
Jingbo