[PATCH 6.6 049/322] SUNRPC: Fix a suspicious RCU usage warning

Greg Kroah-Hartman
2024-02-03T04:11:52Z

From: Anna Schumaker <Anna.Schumaker@Netapp.com>

[ Upstream commit 31b62908693c90d4d07db597e685d9f25a120073 ]

I received the following warning while running cthon against an ontap
server running pNFS:

[ 57.202521] =============================
[ 57.202522] WARNING: suspicious RCU usage
[ 57.202523] 6.7.0-rc3-g2cc14f52aeb7 #41492 Not tainted
[ 57.202525] -----------------------------
[ 57.202525] net/sunrpc/xprtmultipath.c:349 RCU-list traversed in non-reader section!!
[ 57.202527]
other info that might help us debug this:

[ 57.202528]
rcu_scheduler_active = 2, debug_locks = 1
[ 57.202529] no locks held by test5/3567.
[ 57.202530]
stack backtrace:
[ 57.202532] CPU: 0 PID: 3567 Comm: test5 Not tainted 6.7.0-rc3-g2cc14f52aeb7 #41492 5b09971b4965c0aceba19f3eea324a4a806e227e
[ 57.202534] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS unknown 2/2/2022
[ 57.202536] Call Trace:
[ 57.202537] <TASK>
[ 57.202540] dump_stack_lvl+0x77/0xb0
[ 57.202551] lockdep_rcu_suspicious+0x154/0x1a0
[ 57.202556] rpc_xprt_switch_has_addr+0x17c/0x190 [sunrpc ebe02571b9a8ceebf7d98e71675af20c19bdb1f6]
[ 57.202596] rpc_clnt_setup_test_and_add_xprt+0x50/0x180 [sunrpc ebe02571b9a8ceebf7d98e71675af20c19bdb1f6]
[ 57.202621] ? rpc_clnt_add_xprt+0x254/0x300 [sunrpc ebe02571b9a8ceebf7d98e71675af20c19bdb1f6]
[ 57.202646] rpc_clnt_add_xprt+0x27a/0x300 [sunrpc ebe02571b9a8ceebf7d98e71675af20c19bdb1f6]
[ 57.202671] ? __pfx_rpc_clnt_setup_test_and_add_xprt+0x10/0x10 [sunrpc ebe02571b9a8ceebf7d98e71675af20c19bdb1f6]
[ 57.202696] nfs4_pnfs_ds_connect+0x345/0x760 [nfsv4 c716d88496ded0ea6d289bbea684fa996f9b57a9]
[ 57.202728] ? __pfx_nfs4_test_session_trunk+0x10/0x10 [nfsv4 c716d88496ded0ea6d289bbea684fa996f9b57a9]
[ 57.202754] nfs4_fl_prepare_ds+0x75/0xc0 [nfs_layout_nfsv41_files e3a4187f18ae8a27b630f9feae6831b584a9360a]
[ 57.202760] filelayout_write_pagelist+0x4a/0x200 [nfs_layout_nfsv41_files e3a4187f18ae8a27b630f9feae6831b584a9360a]
[ 57.202765] pnfs_generic_pg_writepages+0xbe/0x230 [nfsv4 c716d88496ded0ea6d289bbea684fa996f9b57a9]
[ 57.202788] __nfs_pageio_add_request+0x3fd/0x520 [nfs 6c976fa593a7c2976f5a0aeb4965514a828e6902]
[ 57.202813] nfs_pageio_add_request+0x18b/0x390 [nfs 6c976fa593a7c2976f5a0aeb4965514a828e6902]
[ 57.202831] nfs_do_writepage+0x116/0x1e0 [nfs 6c976fa593a7c2976f5a0aeb4965514a828e6902]
[ 57.202849] nfs_writepages_callback+0x13/0x30 [nfs 6c976fa593a7c2976f5a0aeb4965514a828e6902]
[ 57.202866] write_cache_pages+0x265/0x450
[ 57.202870] ? __pfx_nfs_writepages_callback+0x10/0x10 [nfs 6c976fa593a7c2976f5a0aeb4965514a828e6902]
[ 57.202891] nfs_writepages+0x141/0x230 [nfs 6c976fa593a7c2976f5a0aeb4965514a828e6902]
[ 57.202913] do_writepages+0xd2/0x230
[ 57.202917] ? filemap_fdatawrite_wbc+0x5c/0x80
[ 57.202921] filemap_fdatawrite_wbc+0x67/0x80
[ 57.202924] filemap_write_and_wait_range+0xd9/0x170
[ 57.202930] nfs_wb_all+0x49/0x180 [nfs 6c976fa593a7c2976f5a0aeb4965514a828e6902]
[ 57.202947] nfs4_file_flush+0x72/0xb0 [nfsv4 c716d88496ded0ea6d289bbea684fa996f9b57a9]
[ 57.202969] __se_sys_close+0x46/0xd0
[ 57.202972] do_syscall_64+0x68/0x100
[ 57.202975] ? do_syscall_64+0x77/0x100
[ 57.202976] ? do_syscall_64+0x77/0x100
[ 57.202979] entry_SYSCALL_64_after_hwframe+0x6e/0x76
[ 57.202982] RIP: 0033:0x7fe2b12e4a94
[ 57.202985] Code: 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 80 3d d5 18 0e 00 00 74 13 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 44 c3 0f 1f 00 48 83 ec 18 89 7c 24 0c e8 c3
[ 57.202987] RSP: 002b:00007ffe857ddb38 EFLAGS: 00000202 ORIG_RAX: 0000000000000003
[ 57.202989] RAX: ffffffffffffffda RBX: 00007ffe857dfd68 RCX: 00007fe2b12e4a94
[ 57.202991] RDX: 0000000000002000 RSI: 00007ffe857ddc40 RDI: 0000000000000003
[ 57.202992] RBP: 00007ffe857dfc50 R08: 7fffffffffffffff R09: 0000000065650f49
[ 57.202993] R10: 00007fe2b11f8300 R11: 0000000000000202 R12: 0000000000000000
[ 57.202994] R13: 00007ffe857dfd80 R14: 00007fe2b1445000 R15: 0000000000000000
[ 57.202999] </TASK>

The problem seems to be that two out of three callers aren't taking the
rcu_read_lock() before calling the list_for_each_entry_rcu() function in
rpc_xprt_switch_has_addr(). I fix this by having
rpc_xprt_switch_has_addr() unconditionaly take the rcu_read_lock(),
which is okay to do recursively in the case that the lock has already
been taken by a caller.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sunrpc/xprtmultipath.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/net/sunrpc/xprtmultipath.c b/net/sunrpc/xprtmultipath.c
index 74ee2271251e..720d3ba742ec 100644
--- a/net/sunrpc/xprtmultipath.c
+++ b/net/sunrpc/xprtmultipath.c
@@ -336,8 +336,9 @@ struct rpc_xprt *xprt_iter_current_entry_offline(struct rpc_xprt_iter *xpi)
xprt_switch_find_current_entry_offline);
}

-bool rpc_xprt_switch_has_addr(struct rpc_xprt_switch *xps,
- const struct sockaddr *sap)
+static
+bool __rpc_xprt_switch_has_addr(struct rpc_xprt_switch *xps,
+ const struct sockaddr *sap)
{
struct list_head *head;
struct rpc_xprt *pos;
@@ -356,6 +357,18 @@ bool rpc_xprt_switch_has_addr(struct rpc_xprt_switch *xps,
return false;
}

+bool rpc_xprt_switch_has_addr(struct rpc_xprt_switch *xps,
+ const struct sockaddr *sap)
+{
+ bool res;
+
+ rcu_read_lock();
+ res = __rpc_xprt_switch_has_addr(xps, sap);
+ rcu_read_unlock();
+
+ return res;
+}
+
static
struct rpc_xprt *xprt_switch_find_next_entry(struct list_head *head,
const struct rpc_xprt *cur, bool check_active)
--
2.43.0