[PATCH 6.1.y] ocfs2: fix deadlock in ocfs2_get_system_file_inode

[PATCH 6.1.y] ocfs2: fix deadlock in ocfs2_get_system_file_inode

[Miguel Garcia]

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.com
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: Miguel Garcia <miguelgarciaroman8@gmail.com>
---
 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 bb3a56b7f9a7c..5e86c7e2c8212 100644
--- a/fs/ocfs2/extent_map.c
+++ b/fs/ocfs2/extent_map.c
@@ -981,7 +981,13 @@ 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);
-- 
2.43.0

Re: [PATCH 6.1.y] ocfs2: fix deadlock in ocfs2_get_system_file_inode

[Miguel Garcia]

Please drop this patch. This branch already contains e79c0fc4f61e, a backport of upstream f5b1910e23f1 that removes system_file_mutex and fixes the lock inversion. The older trylock change is unnecessary and can cause failed directory lookups. Sorry for the noise.

Re: [PATCH 6.1.y] ocfs2: fix deadlock in ocfs2_get_system_file_inode

[Sasha Levin]

> Please drop this patch. This branch already contains e79c0fc4f61e, a
> backport of upstream f5b1910e23f1 that removes system_file_mutex and
> fixes the lock inversion. The older trylock change is unnecessary and
> can cause failed directory lookups. Sorry for the noise.

Ack

-- 
Thanks,
Sasha