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Commit 965de0ec authored by Sean Anderson's avatar Sean Anderson Committed by Al Viro
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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 i_mutex is no longer used for locking, and has been superseded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: default avatarSean Anderson <seanga2@gmail.com>
Reviewed-by: default avatarJeff Layton <jlayton@redhat.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 030c7e0b

Documentation/filesystems/Locking

+24 −19
Original line number Diff line number Diff line
@@ -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