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ext4: document lock ordering 

We have enough locks that it's probably worth documenting the lock
ordering rules we have in ext4.

Signed-off-by: Jan Kara <jack@suse.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Jan Kara 2015-12-07 14:35:49 -05:00 committed by Theodore Ts'o
parent 011278485e
commit e74031fd7e
1 changed files with 30 additions and 0 deletions
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30
fs/ext4/super.c
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@ -80,6 +80,36 @@ static void ext4_destroy_lazyinit_thread(void);
static void ext4_unregister_li_request(struct super_block *sb);
static void ext4_clear_request_list(void);
/*
* Lock ordering
*
* Note the difference between i_mmap_sem (EXT4_I(inode)->i_mmap_sem) and
* i_mmap_rwsem (inode->i_mmap_rwsem)!
*
* page fault path:
* mmap_sem -> sb_start_pagefault -> i_mmap_sem (r) -> transaction start ->
* page lock -> i_data_sem (rw)
*
* buffered write path:
* sb_start_write -> i_mutex -> mmap_sem
* sb_start_write -> i_mutex -> transaction start -> page lock ->
* i_data_sem (rw)
*
* truncate:
* sb_start_write -> i_mutex -> EXT4_STATE_DIOREAD_LOCK (w) -> i_mmap_sem (w) ->
* i_mmap_rwsem (w) -> page lock
* sb_start_write -> i_mutex -> EXT4_STATE_DIOREAD_LOCK (w) -> i_mmap_sem (w) ->
* transaction start -> i_data_sem (rw)
*
* direct IO:
* sb_start_write -> i_mutex -> EXT4_STATE_DIOREAD_LOCK (r) -> mmap_sem
* sb_start_write -> i_mutex -> EXT4_STATE_DIOREAD_LOCK (r) ->
* transaction start -> i_data_sem (rw)
*
* writepages:
* transaction start -> page lock(s) -> i_data_sem (rw)
*/
#if !defined(CONFIG_EXT2_FS) && !defined(CONFIG_EXT2_FS_MODULE) && defined(CONFIG_EXT4_USE_FOR_EXT2)
static struct file_system_type ext2_fs_type = {
.owner = THIS_MODULE,