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Commit e74031fd authored by Jan Kara's avatar Jan Kara Committed by Theodore Ts'o
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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: default avatarJan Kara <jack@suse.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 01127848

fs/ext4/super.c

+30 −0
Original line number Diff line number Diff line
@@ -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,