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Subject[PATCH v3 109/110] namei: handle absolute symlinks without dropping out of RCU mode
Date
From: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/namei.c | 30 +++++++++++++++++++-----------
1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 1771143..fc8df8b 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -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;
@@ -780,14 +780,14 @@ 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)
@@ -988,15 +988,23 @@ 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 == '/'))
;
--
2.1.4


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