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SubjectRe: fs/namei.c: Misuse of sequence counts?
Here's a patch for reference (untested):

diff --git a/fs/namei.c b/fs/namei.c
index a7b05bf..84704e4 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -649,17 +649,15 @@ static __always_inline void set_root(struct nameidata *nd)

static int link_path_walk(const char *, struct nameidata *);

-static __always_inline unsigned set_root_rcu(struct nameidata *nd)
+static __always_inline void 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);
} while (read_seqcount_retry(&fs->seq, seq));
- return res;
}

static void path_put_conditional(struct path *path, struct nameidata *nd)
@@ -1854,11 +1852,21 @@ static int path_init(int dfd, const char *name, unsigned int flags,
nd->m_seq = read_seqbegin(&mount_lock);
if (*name=='/') {
if (flags & LOOKUP_RCU) {
+ struct fs_struct *fs = current->fs;
+ unsigned seq;
+
rcu_read_lock();
- nd->seq = set_root_rcu(nd);
+
+ do {
+ seq = read_seqcount_begin(&fs->seq);
+ nd->root = fs->root;
+ nd->inode = nd->root.dentry->d_inode;
+ nd->seq = __read_seqcount_begin(&nd->root.dentry->d_seq);
+ } while (read_seqcount_retry(&fs->seq, seq));
} else {
set_root(nd);
path_get(&nd->root);
+ nd->inode = nd->root.dentry->d_inode;
}
nd->path = nd->root;
} else if (dfd == AT_FDCWD) {
@@ -1871,10 +1879,12 @@ static int path_init(int dfd, const char *name, unsigned int flags,
do {
seq = read_seqcount_begin(&fs->seq);
nd->path = fs->pwd;
+ nd->inode = nd->path.dentry->d_inode;
nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
} while (read_seqcount_retry(&fs->seq, seq));
} else {
get_fs_pwd(current->fs, &nd->path);
+ nd->inode = nd->path.dentry->d_inode;
}
} else {
/* Caller must check execute permissions on the starting path component */
@@ -1894,6 +1904,7 @@ static int path_init(int dfd, const char *name, unsigned int flags,
}

nd->path = f.file->f_path;
+ nd->inode = file_inode(f.file);
if (flags & LOOKUP_RCU) {
if (f.flags & FDPUT_FPUT)
*fp = f.file;
@@ -1904,16 +1915,7 @@ static int path_init(int dfd, const char *name, unsigned int flags,
fdput(f);
}
}
-
- nd->inode = nd->path.dentry->d_inode;
- if (!(flags & LOOKUP_RCU))
- return 0;
- if (likely(!read_seqcount_retry(&nd->path.dentry->d_seq, nd->seq)))
- return 0;
- if (!(nd->flags & LOOKUP_ROOT))
- nd->root.mnt = NULL;
- rcu_read_unlock();
- return -ECHILD;
+ return 0;
}

static inline int lookup_last(struct nameidata *nd, struct path *path)

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