Documentation: filesystems: update filesystem locking documentation

Documentation/filesystems/Locking no longer reflects current locking
semantics. i_mutex is no longer used for locking, and has been superseded
by i_rwsem. Additionally, ->iterate_shared() was not documented.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 75d2d57..15853d5 100644 (file)
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -69,31 +69,31 @@ prototypes:
 
 locking rules:
        all may block
-               i_mutex(inode)
-lookup:                yes
-create:                yes
-link:          yes (both)
-mknod:         yes
-symlink:       yes
-mkdir:         yes
-unlink:                yes (both)
-rmdir:         yes (both)      (see below)
-rename:        yes (all)       (see below)
+               i_rwsem(inode)
+lookup:                shared
+create:                exclusive
+link:          exclusive (both)
+mknod:         exclusive
+symlink:       exclusive
+mkdir:         exclusive
+unlink:                exclusive (both)
+rmdir:         exclusive (both)(see below)
+rename:                exclusive (all) (see below)
 readlink:      no
 get_link:      no
-setattr:       yes
+setattr:       exclusive
 permission:    no (may not block if called in rcu-walk mode)
 get_acl:       no
 getattr:       no
 listxattr:     no
 fiemap:                no
 update_time:   no
-atomic_open:   yes
+atomic_open:   exclusive
 tmpfile:       no
 
 
-       Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
-victim.
+       Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_rwsem
+       exclusive on victim.
        cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
 
 See Documentation/filesystems/directory-locking for more detailed discussion
@@ -111,10 +111,10 @@ prototypes:
 
 locking rules:
        all may block
-               i_mutex(inode)
+               i_rwsem(inode)
 list:          no
 get:           no
-set:           yes
+set:           exclusive
 
 --------------------------- super_operations ---------------------------
 prototypes:
@@ -217,14 +217,14 @@ prototypes:
 locking rules:
        All except set_page_dirty and freepage may block
 
-                       PageLocked(page)        i_mutex
+                       PageLocked(page)        i_rwsem
 writepage:             yes, unlocks (see below)
 readpage:              yes, unlocks
 writepages:
 set_page_dirty         no
 readpages:
-write_begin:           locks the page          yes
-write_end:             yes, unlocks            yes
+write_begin:           locks the page          exclusive
+write_end:             yes, unlocks            exclusive
 bmap:
 invalidatepage:                yes
 releasepage:           yes
@@ -439,6 +439,7 @@ prototypes:
        ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
        ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
        int (*iterate) (struct file *, struct dir_context *);
+       int (*iterate_shared) (struct file *, struct dir_context *);
        unsigned int (*poll) (struct file *, struct poll_table_struct *);
        long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
        long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
@@ -480,6 +481,10 @@ mutex or just to use i_size_read() instead.
 Note: this does not protect the file->f_pos against concurrent modifications
 since this is something the userspace has to take care about.
 
+->iterate() is called with i_rwsem exclusive.
+
+->iterate_shared() is called with i_rwsem at least shared.
+
 ->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
 Most instances call fasync_helper(), which does that maintenance, so it's
 not normally something one needs to worry about.  Return values > 0 will be