Re: [RFC PATCH] 9p: create writeback fid on shared mmap

From: Dominique Martinet <asmadeus@codewreck.org>
To: Chengguang Xu <cgxu519@mykernel.net>
Cc: ericvh@gmail.com, lucho@ionkov.net,
	v9fs-developer@lists.sourceforge.net,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [RFC PATCH] 9p: create writeback fid on shared mmap
Date: Sun, 6 Dec 2020 10:16:18 +0100	[thread overview]
Message-ID: <20201206091618.GA22629@nautica> (raw)
In-Reply-To: <20201205130904.518104-1-cgxu519@mykernel.net>

Chengguang Xu wrote on Sat, Dec 05, 2020:
> If vma is shared and the file was opened for writing,
> we should also create writeback fid because vma may be
> mprotected writable even if now readonly.

Hm, I guess it makes sense.

> Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
> ---
> Caveat: Only compile tested.

Will test later and add it to next then, might be a bit.

>  fs/9p/vfs_file.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
> index b177fd3b1eb3..791839c2dd5c 100644
> --- a/fs/9p/vfs_file.c
> +++ b/fs/9p/vfs_file.c
> @@ -516,8 +516,7 @@ v9fs_mmap_file_mmap(struct file *filp, struct vm_area_struct *vma)
>  	v9inode = V9FS_I(inode);
>  	mutex_lock(&v9inode->v_mutex);
>  	if (!v9inode->writeback_fid &&
> -	    (vma->vm_flags & VM_SHARED) &&
> -	    (vma->vm_flags & VM_WRITE)) {
> +	    mapping_writably_mapped(filp->f_mapping)) {
>  		/*
>  		 * clone a fid and add it to writeback_fid
>  		 * we do it during mmap instead of
-- 
Dominique