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Subject[PATCH] fs: jfs: fix a possible data race in txBegin()
Date
The functions txBegin() and txLazyCommit() can be concurrently executed
in the following call contexts:

Thread1:
jfs_write_inode()
jfs_commit_inode()
txBegin()

Thread2:
jfs_lazycommit()
txLazyCommit()

In txBegin():
tblk->next = tblk->last = tblk->xflag = tblk->flag = tblk->lsn = 0;

In txLazyCommit():
spin_lock_irq(&log->gclock);
...
tblk->flag |= tblkGC_COMMITTED;
...
spin_unlock_irq(&log->gclock);

Thus, a data race can occur for tblk->flag.

To fix this data race, the spinlock log->gclock is used in
txBegin().

This data race is found by our concurrency fuzzer.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
fs/jfs/jfs_txnmgr.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/fs/jfs/jfs_txnmgr.c b/fs/jfs/jfs_txnmgr.c
index c8ce7f1bc594..a1f124aad2e0 100644
--- a/fs/jfs/jfs_txnmgr.c
+++ b/fs/jfs/jfs_txnmgr.c
@@ -415,7 +415,9 @@ tid_t txBegin(struct super_block *sb, int flag)
*
* memset(tblk, 0, sizeof(struct tblock));
*/
+ spin_lock_irq(&log->gclock);
tblk->next = tblk->last = tblk->xflag = tblk->flag = tblk->lsn = 0;
+ spin_unlock_irq(&log->gclock);

tblk->sb = sb;
++log->logtid;
--
2.17.1
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