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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 i_mutex is no longer used for locking, and has been superseded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: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Sean Anderson 2018-05-23 22:29:10 -04:00 committed by Al Viro
parent 030c7e0bb7
commit 965de0ec35
1 changed files with 24 additions and 19 deletions
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43
Documentation/filesystems/Locking
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@ -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