linux-ext4 - [PATCH 5/9] ext4: Document lock ordering

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1445501761-14528-6-git-send-email-jack@suse.com>
Date:	Thu, 22 Oct 2015 10:15:57 +0200
From:	Jan Kara <jack@...e.com>
To:	linux-ext4@...r.kernel.org
Cc:	Ted Tso <tytso@....edu>, Dan Williams <dan.j.williams@...el.com>,
	ross.zwisler@...ux.intel.com, willy@...ux.intel.com,
	Jan Kara <jack@...e.com>
Subject: [PATCH 5/9] 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@...e.com>
---
 fs/ext4/super.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 61fad9e33bb9..152f719a0c62 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -85,6 +85,36 @@ static void ext4_unregister_li_request(struct super_block *sb);
 static void ext4_clear_request_list(void);
 static int ext4_reserve_clusters(struct ext4_sb_info *, ext4_fsblk_t);
 
+/*
+ * 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,
-- 
2.1.4

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html