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non-RCU analogue of the previous commit

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new helper: choose_mountpoint().  Wrapper around choose_mountpoint_rcu(),
similar to lookup_mnt() vs. __lookup_mnt().  follow_dotdot() switched to
it.  Now we don't grab mount_lock exclusive anymore; note that the
primitive used non-RCU mount traversals in other direction (lookup_mnt())
doesn't bother with that either - it uses mount_lock seqcount instead.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2020-02-26 19:19:05 -05:00
parent 7ef482fa65
commit 2aa3847085
1 changed files with 39 additions and 17 deletions
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56
fs/namei.c
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@ -605,10 +605,9 @@ static void terminate_walk(struct nameidata *nd)
}
/* path_put is needed afterwards regardless of success or failure */
static bool legitimize_path(struct nameidata *nd,
struct path *path, unsigned seq)
static bool __legitimize_path(struct path *path, unsigned seq, unsigned mseq)
{
int res = __legitimize_mnt(path->mnt, nd->m_seq);
int res = __legitimize_mnt(path->mnt, mseq);
if (unlikely(res)) {
if (res > 0)
path->mnt = NULL;
@ -622,6 +621,12 @@ static bool legitimize_path(struct nameidata *nd,
return !read_seqcount_retry(&path->dentry->d_seq, seq);
}
static inline bool legitimize_path(struct nameidata *nd,
struct path *path, unsigned seq)
{
return __legitimize_path(path, nd->m_seq, seq);
}
static bool legitimize_links(struct nameidata *nd)
{
int i;
@ -1154,6 +1159,31 @@ static bool choose_mountpoint_rcu(struct mount *m, const struct path *root,
return false;
}
static bool choose_mountpoint(struct mount *m, const struct path *root,
struct path *path)
{
bool found;
rcu_read_lock();
while (1) {
unsigned seq, mseq = read_seqbegin(&mount_lock);
found = choose_mountpoint_rcu(m, root, path, &seq);
if (unlikely(!found)) {
if (!read_seqretry(&mount_lock, mseq))
break;
} else {
if (likely(__legitimize_path(path, seq, mseq)))
break;
rcu_read_unlock();
path_put(path);
rcu_read_lock();
}
}
rcu_read_unlock();
return found;
}
/*
* Perform an automount
* - return -EISDIR to tell follow_managed() to stop and return the path we
@ -1756,22 +1786,14 @@ static struct dentry *follow_dotdot(struct nameidata *nd,
if (path_equal(&nd->path, &nd->root))
goto in_root;
if (unlikely(nd->path.dentry == nd->path.mnt->mnt_root)) {
struct path path = nd->path;
path_get(&path);
while (1) {
if (!follow_up(&path)) {
path_put(&path);
goto in_root;
}
if (path_equal(&path, &nd->root)) {
path_put(&path);
goto in_root;
}
if (path.dentry != nd->path.mnt->mnt_root)
break;
}
struct path path;
if (!choose_mountpoint(real_mount(nd->path.mnt),
&nd->root, &path))
goto in_root;
path_put(&nd->path);
nd->path = path;
nd->inode = path.dentry->d_inode;
if (unlikely(nd->flags & LOOKUP_NO_XDEV))
return ERR_PTR(-EXDEV);
}