From e74031fd7ed0989da8a80364b4d269a57e9c164a Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Mon, 7 Dec 2015 14:35:49 -0500 Subject: [PATCH] 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 Signed-off-by: Theodore Ts'o --- fs/ext4/super.c | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 493370e6590e..486e869bd583 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -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, -- 2.39.5