linux-kernel - [RFC PATCH] 9p: create writeback fid on shared mmap

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Message-ID: <20201205130904.518104-1-cgxu519@mykernel.net>
Date:   Sat,  5 Dec 2020 21:09:04 +0800
From:   Chengguang Xu <cgxu519@...ernel.net>
To:     ericvh@...il.com, lucho@...kov.net, asmadeus@...ewreck.org
Cc:     v9fs-developer@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        Chengguang Xu <cgxu519@...ernel.net>
Subject: [RFC PATCH] 9p: create writeback fid on shared mmap

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.

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

 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
-- 
2.26.2