From: Mohammed Anees pvmohammedanees2003@gmail.com

commit 7bf1823e010e8db2fb649c790bd1b449a75f52d8 upstream.

syzbot has found a possible deadlock in ocfs2_get_system_file_inode [1].

The scenario is depicted here,

CPU0 CPU1 lock(&ocfs2_file_ip_alloc_sem_key); lock(&osb->system_file_mutex); lock(&ocfs2_file_ip_alloc_sem_key); lock(&osb->system_file_mutex);

The function calls which could lead to this are:

CPU0 ocfs2_mknod - lock(&ocfs2_file_ip_alloc_sem_key); . . . ocfs2_get_system_file_inode - lock(&osb->system_file_mutex);

CPU1 - ocfs2_fill_super - lock(&osb->system_file_mutex); . . . ocfs2_read_virt_blocks - lock(&ocfs2_file_ip_alloc_sem_key);

This issue can be resolved by making the down_read -> down_read_try in the ocfs2_read_virt_blocks.

[1] https://syzkaller.appspot.com/bug?extid=e0055ea09f1f5e6fabdd

Link: https://lkml.kernel.org/r/20240924093257.7181-1-pvmohammedanees2003@gmail.co... Signed-off-by: Mohammed Anees pvmohammedanees2003@gmail.com Reviewed-by: Joseph Qi joseph.qi@linux.alibaba.com Reported-by: syzbot+e0055ea09f1f5e6fabdd@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=e0055ea09f1f5e6fabdd Tested-by: syzbot+e0055ea09f1f5e6fabdd@syzkaller.appspotmail.com Cc: Mark Fasheh mark@fasheh.com Cc: Joel Becker jlbec@evilplan.org Cc: Junxiao Bi junxiao.bi@oracle.com Cc: Changwei Ge gechangwei@live.cn Cc: Gang He ghe@suse.com Cc: Jun Piao piaojun@huawei.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Dmitriy Privalov d.privalov@omp.ru --- fs/ocfs2/extent_map.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c index 70a768b623cf..f7672472fa82 100644 --- a/fs/ocfs2/extent_map.c +++ b/fs/ocfs2/extent_map.c @@ -973,7 +973,13 @@ int ocfs2_read_virt_blocks(struct inode *inode, u64 v_block, int nr, }

while (done < nr) { - down_read(&OCFS2_I(inode)->ip_alloc_sem); + if (!down_read_trylock(&OCFS2_I(inode)->ip_alloc_sem)) { + rc = -EAGAIN; + mlog(ML_ERROR, + "Inode #%llu ip_alloc_sem is temporarily unavailable\n", + (unsigned long long)OCFS2_I(inode)->ip_blkno); + break; + } rc = ocfs2_extent_map_get_blocks(inode, v_block + done, &p_block, &p_count, NULL); up_read(&OCFS2_I(inode)->ip_alloc_sem);