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author | Jan Kara <jack@suse.com> | 2015-12-07 14:35:49 -0500 |
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committer | Theodore Ts'o <tytso@mit.edu> | 2015-12-07 14:35:49 -0500 |
commit | e74031fd7ed0989da8a80364b4d269a57e9c164a (patch) | |
tree | 82a6520202b1e4637fbfebd7088058bd42c2e5cd /fs/ext4 | |
parent | 011278485ecc3cd2a3954b5d4c73101d919bf1fa (diff) | |
download | blackbird-obmc-linux-e74031fd7ed0989da8a80364b4d269a57e9c164a.tar.gz blackbird-obmc-linux-e74031fd7ed0989da8a80364b4d269a57e9c164a.zip |
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>
Diffstat (limited to 'fs/ext4')
-rw-r--r-- | fs/ext4/super.c | 30 |
1 files changed, 30 insertions, 0 deletions
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, |