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overlayfs: barriers for opening upper-layer directory

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make sure that
	a) all stores done by opening struct file don't leak past storing
the reference in od->upperfile
	b) the lockless side has read dependency barrier

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2014-10-28 18:27:28 -04:00
parent 54ef6df3f3
commit d45f00ae43
1 changed files with 2 additions and 1 deletions
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3
fs/overlayfs/readdir.c
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@ -454,12 +454,13 @@ static int ovl_dir_fsync(struct file *file, loff_t start, loff_t end,
if (!od->is_upper && ovl_path_type(dentry) == OVL_PATH_MERGE) {
struct inode *inode = file_inode(file);
realfile = od->upperfile;
realfile =lockless_dereference(od->upperfile);
if (!realfile) {
struct path upperpath;
ovl_path_upper(dentry, &upperpath);
realfile = ovl_path_open(&upperpath, O_RDONLY);
smp_mb__before_spinlock();
mutex_lock(&inode->i_mutex);
if (!od->upperfile) {
if (IS_ERR(realfile)) {