blob: a53516c16c5bc69318f647d124f4be80143e7b4f [file] [log] [blame]
From 9552114287b78d0ce4e02ddea17b26250fd3903b Mon Sep 17 00:00:00 2001
From: Qian Cai <>
Date: Fri, 21 Feb 2020 23:31:11 -0500
Subject: [PATCH] jbd2: fix data races at struct journal_head
commit 6c5d911249290f41f7b50b43344a7520605b1acb upstream.
journal_head::b_transaction and journal_head::b_next_transaction could
be accessed concurrently as noticed by KCSAN,
LTP: starting fsync04
/dev/zero: Can't open blockdev
EXT4-fs (loop0): mounting ext3 file system using the ext4 subsystem
EXT4-fs (loop0): mounted filesystem with ordered data mode. Opts: (null)
BUG: KCSAN: data-race in __jbd2_journal_refile_buffer [jbd2] / jbd2_write_access_granted [jbd2]
write to 0xffff99f9b1bd0e30 of 8 bytes by task 25721 on cpu 70:
__jbd2_journal_refile_buffer+0xdd/0x210 [jbd2]
__jbd2_journal_refile_buffer at fs/jbd2/transaction.c:2569
jbd2_journal_commit_transaction+0x2d15/0x3f20 [jbd2]
(inlined by) jbd2_journal_commit_transaction at fs/jbd2/commit.c:1034
kjournald2+0x13b/0x450 [jbd2]
read to 0xffff99f9b1bd0e30 of 8 bytes by task 25724 on cpu 68:
jbd2_write_access_granted+0x1b2/0x250 [jbd2]
jbd2_write_access_granted at fs/jbd2/transaction.c:1155
jbd2_journal_get_write_access+0x2c/0x60 [jbd2]
__ext4_journal_get_write_access+0x50/0x90 [ext4]
ext4_mb_mark_diskspace_used+0x158/0x620 [ext4]
ext4_mb_new_blocks+0x54f/0xca0 [ext4]
ext4_ind_map_blocks+0xc79/0x1b40 [ext4]
ext4_map_blocks+0x3b4/0x950 [ext4]
_ext4_get_block+0xfc/0x270 [ext4]
ext4_get_block+0x3b/0x50 [ext4]
ext4_write_begin+0x388/0xb50 [ext4]
ext4_buffered_write_iter+0x11f/0x210 [ext4]
ext4_file_write_iter+0xce/0x9e0 [ext4]
5 locks held by fsync04/25724:
#0: ffff99f9911093f8 (sb_writers#13){.+.+}, at: vfs_write+0x21c/0x260
#1: ffff99f9db4c0348 (&sb->s_type->i_mutex_key#15){+.+.}, at: ext4_buffered_write_iter+0x65/0x210 [ext4]
#2: ffff99f5e7dfcf58 (jbd2_handle){++++}, at: start_this_handle+0x1c1/0x9d0 [jbd2]
#3: ffff99f9db4c0168 (&ei->i_data_sem){++++}, at: ext4_map_blocks+0x176/0x950 [ext4]
#4: ffffffff99086b40 (rcu_read_lock){....}, at: jbd2_write_access_granted+0x4e/0x250 [jbd2]
irq event stamp: 1407125
hardirqs last enabled at (1407125): [<ffffffff980da9b7>] __find_get_block+0x107/0x790
hardirqs last disabled at (1407124): [<ffffffff980da8f9>] __find_get_block+0x49/0x790
softirqs last enabled at (1405528): [<ffffffff98a0034c>] __do_softirq+0x34c/0x57c
softirqs last disabled at (1405521): [<ffffffff97cc67a2>] irq_exit+0xa2/0xc0
Reported by Kernel Concurrency Sanitizer on:
CPU: 68 PID: 25724 Comm: fsync04 Tainted: G L 5.6.0-rc2-next-20200221+ #7
Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
The plain reads are outside of jh->b_state_lock critical section which result
in data races. Fix them by adding pairs of READ|WRITE_ONCE().
Reviewed-by: Jan Kara <>
Signed-off-by: Qian Cai <>
Signed-off-by: Theodore Ts'o <>
Signed-off-by: Paul Gortmaker <>
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index e0a5dd48a8a9..f6163da64bb5 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1076,8 +1076,8 @@ static bool jbd2_write_access_granted(handle_t *handle, struct buffer_head *bh,
/* For undo access buffer must have data copied */
if (undo && !jh->b_committed_data)
goto out;
- if (jh->b_transaction != handle->h_transaction &&
- jh->b_next_transaction != handle->h_transaction)
+ if (READ_ONCE(jh->b_transaction) != handle->h_transaction &&
+ READ_ONCE(jh->b_next_transaction) != handle->h_transaction)
goto out;
* There are two reasons for the barrier here:
@@ -2532,8 +2532,8 @@ void __jbd2_journal_refile_buffer(struct journal_head *jh)
* our jh reference and thus __jbd2_journal_file_buffer() must not
* take a new one.
- jh->b_transaction = jh->b_next_transaction;
- jh->b_next_transaction = NULL;
+ WRITE_ONCE(jh->b_transaction, jh->b_next_transaction);
+ WRITE_ONCE(jh->b_next_transaction, NULL);
if (buffer_freed(bh))
jlist = BJ_Forget;
else if (jh->b_modified)