Re: [syzbot] [nfs?] INFO: task hung in nfsd_nl_listener_get_doit

[Lorenzo Bianconi <lorenzo@kernel.org>]

[-- Attachment #1: Type: text/plain, Size: 10492 bytes --]

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    cea2a26553ac mailmap: Add my outdated addresses to the map..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=169fd8ee980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=fa0ce06dcc735711
> dashboard link: https://syzkaller.appspot.com/bug?extid=4207adf14e7c0981d28d
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/1f7ce933512f/disk-cea2a265.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/0ce3b9940616/vmlinux-cea2a265.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/19e24094ea37/bzImage-cea2a265.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+4207adf14e7c0981d28d@syzkaller.appspotmail.com
> 
> INFO: task syz-executor.1:17770 blocked for more than 143 seconds.
>       Not tainted 6.10.0-rc3-syzkaller-00022-gcea2a26553ac #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:syz-executor.1  state:D stack:23800 pid:17770 tgid:17767 ppid:11381  flags:0x00000006
> Call Trace:
>  <TASK>
>  context_switch kernel/sched/core.c:5408 [inline]
>  __schedule+0x17e8/0x4a20 kernel/sched/core.c:6745
>  __schedule_loop kernel/sched/core.c:6822 [inline]
>  schedule+0x14b/0x320 kernel/sched/core.c:6837
>  schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6894
>  __mutex_lock_common kernel/locking/mutex.c:684 [inline]
>  __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
>  nfsd_nl_listener_get_doit+0x115/0x5d0 fs/nfsd/nfsctl.c:2124
>  genl_family_rcv_msg_doit net/netlink/genetlink.c:1115 [inline]
>  genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
>  genl_rcv_msg+0xb16/0xec0 net/netlink/genetlink.c:1210
>  netlink_rcv_skb+0x1e5/0x430 net/netlink/af_netlink.c:2564
>  genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
>  netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
>  netlink_unicast+0x7ec/0x980 net/netlink/af_netlink.c:1361
>  netlink_sendmsg+0x8db/0xcb0 net/netlink/af_netlink.c:1905
>  sock_sendmsg_nosec net/socket.c:730 [inline]
>  __sock_sendmsg+0x223/0x270 net/socket.c:745
>  ____sys_sendmsg+0x525/0x7d0 net/socket.c:2585
>  ___sys_sendmsg net/socket.c:2639 [inline]
>  __sys_sendmsg+0x2b0/0x3a0 net/socket.c:2668
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f24ed27cea9
> RSP: 002b:00007f24ee0080c8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00007f24ed3b3f80 RCX: 00007f24ed27cea9
> RDX: 0000000000000000 RSI: 0000000020000100 RDI: 0000000000000005
> RBP: 00007f24ed2ebff4 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup
> 

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git 4ddfda417a50

From be9676fba16c0b8769c3b6094f35da39b1ba3953 Mon Sep 17 00:00:00 2001
Message-ID: <be9676fba16c0b8769c3b6094f35da39b1ba3953.1718640518.git.lorenzo@kernel.org>
From: Lorenzo Bianconi <lorenzo@kernel.org>
Date: Mon, 17 Jun 2024 16:26:26 +0200
Subject: [PATCH] NFSD: grab nfsd_mutex in nfsd_nl_rpc_status_get_dumpit()

Grab nfsd_mutex lock in nfsd_nl_rpc_status_get_dumpit routine and remove
nfsd_nl_rpc_status_get_start() and nfsd_nl_rpc_status_get_done(). This
patch fix the syzbot log reported below:

INFO: task syz-executor.1:17770 blocked for more than 143 seconds.
      Not tainted 6.10.0-rc3-syzkaller-00022-gcea2a26553ac #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.1  state:D stack:23800 pid:17770 tgid:17767 ppid:11381  flags:0x00000006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5408 [inline]
 __schedule+0x17e8/0x4a20 kernel/sched/core.c:6745
 __schedule_loop kernel/sched/core.c:6822 [inline]
 schedule+0x14b/0x320 kernel/sched/core.c:6837
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6894
 __mutex_lock_common kernel/locking/mutex.c:684 [inline]
 __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
 nfsd_nl_listener_get_doit+0x115/0x5d0 fs/nfsd/nfsctl.c:2124
 genl_family_rcv_msg_doit net/netlink/genetlink.c:1115 [inline]
 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
 genl_rcv_msg+0xb16/0xec0 net/netlink/genetlink.c:1210
 netlink_rcv_skb+0x1e5/0x430 net/netlink/af_netlink.c:2564
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
 netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
 netlink_unicast+0x7ec/0x980 net/netlink/af_netlink.c:1361
 netlink_sendmsg+0x8db/0xcb0 net/netlink/af_netlink.c:1905
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg+0x223/0x270 net/socket.c:745
 ____sys_sendmsg+0x525/0x7d0 net/socket.c:2585
 ___sys_sendmsg net/socket.c:2639 [inline]
 __sys_sendmsg+0x2b0/0x3a0 net/socket.c:2668
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f24ed27cea9
RSP: 002b:00007f24ee0080c8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f24ed3b3f80 RCX: 00007f24ed27cea9
RDX: 0000000000000000 RSI: 0000000020000100 RDI: 0000000000000005
RBP: 00007f24ed2ebff4 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000

Fixes: 1bd773b4f0c9 ("nfsd: hold nfsd_mutex across entire netlink operation")
Fixes: bd9d6a3efa97 ("NFSD: add rpc_status netlink support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 Documentation/netlink/specs/nfsd.yaml |  2 --
 fs/nfsd/netlink.c                     |  2 --
 fs/nfsd/netlink.h                     |  3 --
 fs/nfsd/nfsctl.c                      | 48 ++++++---------------------
 4 files changed, 11 insertions(+), 44 deletions(-)

diff --git a/Documentation/netlink/specs/nfsd.yaml b/Documentation/netlink/specs/nfsd.yaml
index 5a98e5a06c68..c87658114852 100644
--- a/Documentation/netlink/specs/nfsd.yaml
+++ b/Documentation/netlink/specs/nfsd.yaml
@@ -132,8 +132,6 @@ operations:
       doc: dump pending nfsd rpc
       attribute-set: rpc-status
       dump:
-        pre: nfsd-nl-rpc-status-get-start
-        post: nfsd-nl-rpc-status-get-done
         reply:
           attributes:
             - xid
diff --git a/fs/nfsd/netlink.c b/fs/nfsd/netlink.c
index 137701153c9e..ca54aa583530 100644
--- a/fs/nfsd/netlink.c
+++ b/fs/nfsd/netlink.c
@@ -49,9 +49,7 @@ static const struct nla_policy nfsd_pool_mode_set_nl_policy[NFSD_A_POOL_MODE_MOD
 static const struct genl_split_ops nfsd_nl_ops[] = {
 	{
 		.cmd	= NFSD_CMD_RPC_STATUS_GET,
-		.start	= nfsd_nl_rpc_status_get_start,
 		.dumpit	= nfsd_nl_rpc_status_get_dumpit,
-		.done	= nfsd_nl_rpc_status_get_done,
 		.flags	= GENL_CMD_CAP_DUMP,
 	},
 	{
diff --git a/fs/nfsd/netlink.h b/fs/nfsd/netlink.h
index 9459547de04e..8eb903f24c41 100644
--- a/fs/nfsd/netlink.h
+++ b/fs/nfsd/netlink.h
@@ -15,9 +15,6 @@
 extern const struct nla_policy nfsd_sock_nl_policy[NFSD_A_SOCK_TRANSPORT_NAME + 1];
 extern const struct nla_policy nfsd_version_nl_policy[NFSD_A_VERSION_ENABLED + 1];
 
-int nfsd_nl_rpc_status_get_start(struct netlink_callback *cb);
-int nfsd_nl_rpc_status_get_done(struct netlink_callback *cb);
-
 int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
 				  struct netlink_callback *cb);
 int nfsd_nl_threads_set_doit(struct sk_buff *skb, struct genl_info *info);
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index e5d2cc74ef77..78091a73b33b 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1468,28 +1468,6 @@ static int create_proc_exports_entry(void)
 
 unsigned int nfsd_net_id;
 
-/**
- * nfsd_nl_rpc_status_get_start - Prepare rpc_status_get dumpit
- * @cb: netlink metadata and command arguments
- *
- * Return values:
- *   %0: The rpc_status_get command may proceed
- *   %-ENODEV: There is no NFSD running in this namespace
- */
-int nfsd_nl_rpc_status_get_start(struct netlink_callback *cb)
-{
-	struct nfsd_net *nn = net_generic(sock_net(cb->skb->sk), nfsd_net_id);
-	int ret = -ENODEV;
-
-	mutex_lock(&nfsd_mutex);
-	if (nn->nfsd_serv)
-		ret = 0;
-	else
-		mutex_unlock(&nfsd_mutex);
-
-	return ret;
-}
-
 static int nfsd_genl_rpc_status_compose_msg(struct sk_buff *skb,
 					    struct netlink_callback *cb,
 					    struct nfsd_genl_rqstp *rqstp)
@@ -1566,8 +1544,16 @@ static int nfsd_genl_rpc_status_compose_msg(struct sk_buff *skb,
 int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
 				  struct netlink_callback *cb)
 {
-	struct nfsd_net *nn = net_generic(sock_net(skb->sk), nfsd_net_id);
 	int i, ret, rqstp_index = 0;
+	struct nfsd_net *nn;
+
+	mutex_lock(&nfsd_mutex);
+
+	nn = net_generic(sock_net(skb->sk), nfsd_net_id);
+	if (!nn->nfsd_serv) {
+		ret = -ENODEV;
+		goto out_unlock;
+	}
 
 	rcu_read_lock();
 
@@ -1644,22 +1630,10 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
 	ret = skb->len;
 out:
 	rcu_read_unlock();
-
-	return ret;
-}
-
-/**
- * nfsd_nl_rpc_status_get_done - rpc_status_get dumpit post-processing
- * @cb: netlink metadata and command arguments
- *
- * Return values:
- *   %0: Success
- */
-int nfsd_nl_rpc_status_get_done(struct netlink_callback *cb)
-{
+out_unlock:
 	mutex_unlock(&nfsd_mutex);
 
-	return 0;
+	return ret;
 }
 
 /**
-- 
2.45.1



[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]