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Message-ID: <20240924093257.7181-1-pvmohammedanees2003@gmail.com>
Date: Tue, 24 Sep 2024 09:32:57 +0000
From: Mohammed Anees <pvmohammedanees2003@...il.com>
To: ocfs2-devel@...ts.linux.dev,
linux-kernel@...r.kernel.org
Cc: Mark Fasheh <mark@...heh.com>,
Joel Becker <jlbec@...lplan.org>,
Joseph Qi <joseph.qi@...ux.alibaba.com>,
Mohammed Anees <pvmohammedanees2003@...il.com>,
syzbot+e0055ea09f1f5e6fabdd@...kaller.appspotmail.com
Subject: [PATCH v3] ocfs2: Fix deadlock in ocfs2_get_system_file_inode
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
Reported-and-tested-by: syzbot+e0055ea09f1f5e6fabdd@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=e0055ea09f1f5e6fabdd
Signed-off-by: Mohammed Anees <pvmohammedanees2003@...il.com>
---
v3:
- Removed multiple if conditions
---
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 70a768b62..f7672472f 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);
--
2.46.0
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