In ext4_buffered_write_iter(), generic_write_sync() is being called at the same time by two different CPUs. This causes a data-race for inode->i_state. To prevent this, make generic_write_sync() a critical section in ext4_buffered_write_iter(). Use mutex to allow preemption so other CPU is not blocked while waiting. Signed-off-by: Daniel Yang <danielyangkang@xxxxxxxxx> Reported-by: syzbot+a388a53633c9a4e9b22e@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://syzkaller.appspot.com/bug?extid=a388a53633c9a4e9b22e --- fs/ext4/file.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/fs/ext4/file.c b/fs/ext4/file.c index f14aed14b..ce1251d3b 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -19,6 +19,7 @@ * (jj@xxxxxxxxxxxxxxxxxxxxxx) */ +#include "linux/mutex.h" #include <linux/time.h> #include <linux/fs.h> #include <linux/iomap.h> @@ -282,6 +283,9 @@ static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from) return count; } +/* lock for critical section of generic_write_sync */ +static DEFINE_MUTEX(write_sync_lock); + static ssize_t ext4_buffered_write_iter(struct kiocb *iocb, struct iov_iter *from) { @@ -302,7 +306,13 @@ static ssize_t ext4_buffered_write_iter(struct kiocb *iocb, inode_unlock(inode); if (unlikely(ret <= 0)) return ret; - return generic_write_sync(iocb, ret); + + /* prevent read-write data race */ + mutex_lock(&write_sync_lock); + ret = generic_write_sync(iocb, ret); + mutex_unlock(&write_sync_lock); + + return ret; } static ssize_t ext4_handle_inode_extension(struct inode *inode, loff_t offset, -- 2.39.2
