[PATCH 4.19 220/346] nfs_common: need lock during iterate through the list

Greg Kroah-Hartman
2020-12-28T13:32:24Z

From: Cheng Lin <cheng.lin130@zte.com.cn>

[ Upstream commit 4a9d81caf841cd2c0ae36abec9c2963bf21d0284 ]

If the elem is deleted during be iterated on it, the iteration
process will fall into an endless loop.

kernel: NMI watchdog: BUG: soft lockup - CPU#4 stuck for 22s! [nfsd:17137]

PID: 17137  TASK: ffff8818d93c0000  CPU: 4   COMMAND: "nfsd"
[exception RIP: __state_in_grace+76]
RIP: ffffffffc00e817c  RSP: ffff8818d3aefc98  RFLAGS: 00000246
RAX: ffff881dc0c38298  RBX: ffffffff81b03580  RCX: ffff881dc02c9f50
RDX: ffff881e3fce8500  RSI: 0000000000000001  RDI: ffffffff81b03580
RBP: ffff8818d3aefca0   R8: 0000000000000020   R9: ffff8818d3aefd40
R10: ffff88017fc03800  R11: ffff8818e83933c0  R12: ffff8818d3aefd40
R13: 0000000000000000  R14: ffff8818e8391068  R15: ffff8818fa6e4000
CS: 0010  SS: 0018
#0 [ffff8818d3aefc98] opens_in_grace at ffffffffc00e81e3 [grace]
#1 [ffff8818d3aefca8] nfs4_preprocess_stateid_op at ffffffffc02a3e6c [nfsd]
#2 [ffff8818d3aefd18] nfsd4_write at ffffffffc028ed5b [nfsd]
#3 [ffff8818d3aefd80] nfsd4_proc_compound at ffffffffc0290a0d [nfsd]
#4 [ffff8818d3aefdd0] nfsd_dispatch at ffffffffc027b800 [nfsd]
#5 [ffff8818d3aefe08] svc_process_common at ffffffffc02017f3 [sunrpc]
#6 [ffff8818d3aefe70] svc_process at ffffffffc0201ce3 [sunrpc]
#7 [ffff8818d3aefe98] nfsd at ffffffffc027b117 [nfsd]
#8 [ffff8818d3aefec8] kthread at ffffffff810b88c1
#9 [ffff8818d3aeff50] ret_from_fork at ffffffff816d1607

The troublemake elem:
crash> lock_manager ffff881dc0c38298
struct lock_manager {
list = {
next = 0xffff881dc0c38298,
prev = 0xffff881dc0c38298
},
block_opens = false
}

Fixes: c87fb4a378f9 ("lockd: NLM grace period shouldn't block NFSv4 opens")
Signed-off-by: Cheng Lin <cheng.lin130@zte.com.cn>
Signed-off-by: Yi Wang <wang.yi59@zte.com.cn>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/nfs_common/grace.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/nfs_common/grace.c b/fs/nfs_common/grace.c
index 5be08f02a76bc..4f90c444907f5 100644
--- a/fs/nfs_common/grace.c
+++ b/fs/nfs_common/grace.c
@@ -68,10 +68,14 @@ __state_in_grace(struct net *net, bool open)
if (!open)
return !list_empty(grace_list);

+ spin_lock(&grace_lock);
list_for_each_entry(lm, grace_list, list) {
- if (lm->block_opens)
+ if (lm->block_opens) {
+ spin_unlock(&grace_lock);
return true;
+ }
}
+ spin_unlock(&grace_lock);
return false;
}

--
2.27.0