3 files changed, 34 insertions, 13 deletions

diff --git a/fs/fs_struct.c b/fs/fs_struct.c
index ed45a9cf5f3d..60b8531f41c5 100644
--- a/fs/fs_struct.c
+++ b/fs/fs_struct.c
@@ -14,9 +14,11 @@ void set_fs_root(struct fs_struct *fs, struct path *path)
         struct path old_root;
 
         spin_lock(&fs->lock);
+        write_seqcount_begin(&fs->seq);
         old_root = fs->root;
         fs->root = *path;
         path_get(path);
+        write_seqcount_end(&fs->seq);
         spin_unlock(&fs->lock);
         if (old_root.dentry)
                 path_put(&old_root);
@@ -31,9 +33,11 @@ void set_fs_pwd(struct fs_struct *fs, struct path *path)
         struct path old_pwd;
 
         spin_lock(&fs->lock);
+        write_seqcount_begin(&fs->seq);
         old_pwd = fs->pwd;
         fs->pwd = *path;
         path_get(path);
+        write_seqcount_end(&fs->seq);
         spin_unlock(&fs->lock);
 
         if (old_pwd.dentry)
@@ -52,6 +56,7 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root)
                 fs = p->fs;
                 if (fs) {
                         spin_lock(&fs->lock);
+                        write_seqcount_begin(&fs->seq);
                         if (fs->root.dentry == old_root->dentry
                             && fs->root.mnt == old_root->mnt) {
                                 path_get(new_root);
@@ -64,6 +69,7 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root)
                                 fs->pwd = *new_root;
                                 count++;
                         }
+                        write_seqcount_end(&fs->seq);
                         spin_unlock(&fs->lock);
                 }
                 task_unlock(p);
@@ -88,8 +94,10 @@ void exit_fs(struct task_struct *tsk)
                 int kill;
                 task_lock(tsk);
                 spin_lock(&fs->lock);
+                write_seqcount_begin(&fs->seq);
                 tsk->fs = NULL;
                 kill = !--fs->users;
+                write_seqcount_end(&fs->seq);
                 spin_unlock(&fs->lock);
                 task_unlock(tsk);
                 if (kill)
@@ -105,6 +113,7 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old)
                 fs->users = 1;
                 fs->in_exec = 0;
                 spin_lock_init(&fs->lock);
+                seqcount_init(&fs->seq);
                 fs->umask = old->umask;
                 get_fs_root_and_pwd(old, &fs->root, &fs->pwd);
         }
@@ -144,6 +153,7 @@ EXPORT_SYMBOL(current_umask);
 struct fs_struct init_fs = {
         .users          = 1,
         .lock           = __SPIN_LOCK_UNLOCKED(init_fs.lock),
+        .seq            = SEQCNT_ZERO,
         .umask          = 0022,
 };
 
diff --git a/fs/namei.c b/fs/namei.c
index 8d3f15b3a541..c731b50a6184 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -684,9 +684,12 @@ static __always_inline void set_root_rcu(struct nameidata *nd)
 {
         if (!nd->root.mnt) {
                 struct fs_struct *fs = current->fs;
-                spin_lock(&fs->lock);
-                nd->root = fs->root;
-                spin_unlock(&fs->lock);
+                unsigned seq;
+
+                do {
+                        seq = read_seqcount_begin(&fs->seq);
+                        nd->root = fs->root;
+                } while (read_seqcount_retry(&fs->seq, seq));
         }
 }
 
@@ -1369,26 +1372,31 @@ static int path_init_rcu(int dfd, const char *name, unsigned int flags, struct n
 
         if (*name=='/') {
                 struct fs_struct *fs = current->fs;
+                unsigned seq;
 
                 br_read_lock(vfsmount_lock);
                 rcu_read_lock();
 
-                spin_lock(&fs->lock);
-                nd->root = fs->root;
-                nd->path = nd->root;
-                nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
-                spin_unlock(&fs->lock);
+                do {
+                        seq = read_seqcount_begin(&fs->seq);
+                        nd->root = fs->root;
+                        nd->path = nd->root;
+                        nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
+                } while (read_seqcount_retry(&fs->seq, seq));
 
         } else if (dfd == AT_FDCWD) {
                 struct fs_struct *fs = current->fs;
+                unsigned seq;
 
                 br_read_lock(vfsmount_lock);
                 rcu_read_lock();
 
-                spin_lock(&fs->lock);
-                nd->path = fs->pwd;
-                nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
-                spin_unlock(&fs->lock);
+                do {
+                        seq = read_seqcount_begin(&fs->seq);
+                        nd->path = fs->pwd;
+                        nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
+                } while (read_seqcount_retry(&fs->seq, seq));
+
         } else {
                 struct dentry *dentry;
 
@@ -1411,7 +1419,7 @@ static int path_init_rcu(int dfd, const char *name, unsigned int flags, struct n
                 if (fput_needed)
                         nd->file = file;
 
-                nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
+                nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
                 br_read_lock(vfsmount_lock);
                 rcu_read_lock();
         }
diff --git a/include/linux/fs_struct.h b/include/linux/fs_struct.h
index a42b5bf02f8b..003dc0fd7347 100644
--- a/include/linux/fs_struct.h
+++ b/include/linux/fs_struct.h
@@ -2,10 +2,13 @@
 #define _LINUX_FS_STRUCT_H
 
 #include <linux/path.h>
+#include <linux/spinlock.h>
+#include <linux/seqlock.h>
 
 struct fs_struct {
         int users;
         spinlock_t lock;
+        seqcount_t seq;
         int umask;
         int in_exec;
         struct path root, pwd;