linux-kernel - [PATCH] ceph: fix deadlock in ceph_readdir

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Message-ID: <20250730094123.30540-1-sunzhao03@kuaishou.com>
Date: Wed, 30 Jul 2025 17:41:23 +0800
From: Zhao Sun <sunzhao03@...ishou.com>
To: <xiubli@...hat.com>, <idryomov@...il.com>
CC: <ceph-devel@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Zhao Sun
	<sunzhao03@...ishou.com>
Subject: [PATCH] ceph: fix deadlock in ceph_readdir_prepopulate

When ceph_readdir_prepopulate calls ceph_get_inode while holding
mdsc->snap_rwsem, a deadlock may occur, blocking all subsequent
requests of the current session.

Fix by release the mds->snap_rwsem read lock before calling the
ceph_get_inode function.

Link: https://tracker.ceph.com/issues/72307
Signed-off-by: Zhao Sun <sunzhao03@...ishou.com>
---
 fs/ceph/inode.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index 06cd2963e41e..3d7fb045ba76 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -1900,6 +1900,7 @@ static int fill_readdir_cache(struct inode *dir, struct dentry *dn,
 int ceph_readdir_prepopulate(struct ceph_mds_request *req,
 			     struct ceph_mds_session *session)
 {
+	struct ceph_mds_client *mdsc = session->s_mdsc;
 	struct dentry *parent = req->r_dentry;
 	struct inode *inode = d_inode(parent);
 	struct ceph_inode_info *ci = ceph_inode(inode);
@@ -2029,7 +2030,10 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
 		if (d_really_is_positive(dn)) {
 			in = d_inode(dn);
 		} else {
+			/* Release mdsc->snap_rwsem in advance to avoid deadlock */
+			up_read(&mdsc->snap_rwsem);
 			in = ceph_get_inode(parent->d_sb, tvino, NULL);
+			down_read(&mdsc->snap_rwsem);
 			if (IS_ERR(in)) {
 				doutc(cl, "new_inode badness\n");
 				d_drop(dn);
-- 
2.39.2 (Apple Git-143)