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namei: handle absolute symlinks without dropping out of RCU mode 

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2015-05-09 19:02:01 -04:00
parent 8c1b456689
commit 8f47a0167c
1 changed files with 20 additions and 11 deletions
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31
fs/namei.c
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@ -499,7 +499,7 @@ struct nameidata {
struct path root;
struct inode *inode; /* path.dentry.d_inode */
unsigned int flags;
unsigned seq, m_seq;
unsigned seq, m_seq, root_seq;
int last_type;
unsigned depth;
int total_link_count;
@ -788,14 +788,14 @@ static __always_inline void set_root(struct nameidata *nd)
static __always_inline unsigned set_root_rcu(struct nameidata *nd)
{
struct fs_struct *fs = current->fs;
unsigned seq, res;
unsigned seq;
do {
seq = read_seqcount_begin(&fs->seq);
nd->root = fs->root;
res = __read_seqcount_begin(&nd->root.dentry->d_seq);
nd->root_seq = __read_seqcount_begin(&nd->root.dentry->d_seq);
} while (read_seqcount_retry(&fs->seq, seq));
return res;
return nd->root_seq;
}
static void path_put_conditional(struct path *path, struct nameidata *nd)
@ -995,15 +995,23 @@ const char *get_link(struct nameidata *nd)
}
if (*res == '/') {
if (nd->flags & LOOKUP_RCU) {
if (unlikely(unlazy_walk(nd, NULL, 0)))
struct dentry *d;
if (!nd->root.mnt)
set_root_rcu(nd);
nd->path = nd->root;
d = nd->path.dentry;
nd->inode = d->d_inode;
nd->seq = nd->root_seq;
if (unlikely(read_seqcount_retry(&d->d_seq, nd->seq)))
return ERR_PTR(-ECHILD);
} else {
if (!nd->root.mnt)
set_root(nd);
path_put(&nd->path);
nd->path = nd->root;
path_get(&nd->root);
nd->inode = nd->path.dentry->d_inode;
}
if (!nd->root.mnt)
set_root(nd);
path_put(&nd->path);
nd->path = nd->root;
path_get(&nd->root);
nd->inode = nd->path.dentry->d_inode;
nd->flags |= LOOKUP_JUMPED;
while (unlikely(*++res == '/'))
;
@ -1979,6 +1987,7 @@ static const char *path_init(int dfd, const struct filename *name,
if (flags & LOOKUP_RCU) {
rcu_read_lock();
nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
nd->root_seq = nd->seq;
nd->m_seq = read_seqbegin(&mount_lock);
} else {
path_get(&nd->path);