fs: increase d_name lock coverage

Cover d_name with d_lock in more cases, where there may be concurrent
modification to it.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

1 files changed, 12 insertions, 2 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index de38680ee0ed..a09f0771fd27 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1350,6 +1350,11 @@ static struct dentry *__d_instantiate_unique(struct dentry *entry,
         list_for_each_entry(alias, &inode->i_dentry, d_alias) {
                 struct qstr *qstr = &alias->d_name;
 
+                /*
+                 * Don't need alias->d_lock here, because aliases with
+                 * d_parent == entry->d_parent are not subject to name or
+                 * parent changes, because the parent inode i_mutex is held.
+                 */
                 if (qstr->hash != hash)
                         continue;
                 if (alias->d_parent != entry->d_parent)
@@ -2313,7 +2318,9 @@ static int prepend_path(const struct path *path, struct path *root,
                 }
                 parent = dentry->d_parent;
                 prefetch(parent);
+                spin_lock(&dentry->d_lock);
                 error = prepend_name(buffer, buflen, &dentry->d_name);
+                spin_unlock(&dentry->d_lock);
                 if (!error)
                         error = prepend(buffer, buflen, "/", 1);
                 if (error)
@@ -2515,10 +2522,13 @@ static char *__dentry_path(struct dentry *dentry, char *buf, int buflen)
 
         while (!IS_ROOT(dentry)) {
                 struct dentry *parent = dentry->d_parent;
+                int error;
 
                 prefetch(parent);
-                if ((prepend_name(&end, &buflen, &dentry->d_name) != 0) ||
-                    (prepend(&end, &buflen, "/", 1) != 0))
+                spin_lock(&dentry->d_lock);
+                error = prepend_name(&end, &buflen, &dentry->d_name);
+                spin_unlock(&dentry->d_lock);
+                if (error != 0 || prepend(&end, &buflen, "/", 1) != 0)
                         goto Elong;
 
                 retval = end;