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Message-ID: <18dc97cae8ead7137edfab8ffec1b5fdd0dc914e.camel@kernel.org>
Subject: Re: [PATCH v2 4/4] SUNRPC: Fix a suspicious RCU usage warning
From: Jeff Layton <jlayton@kernel.org>
To: Anna Schumaker <anna@kernel.org>, linux-nfs@vger.kernel.org, 
	trond.myklebust@hammerspace.com
Date: Tue, 05 Dec 2023 05:51:06 -0500
In-Reply-To: <20231204202512.108047-5-anna@kernel.org>
References: <20231204202512.108047-1-anna@kernel.org>
	 <20231204202512.108047-5-anna@kernel.org>
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On Mon, 2023-12-04 at 15:25 -0500, Anna Schumaker wrote:
> From: Anna Schumaker <Anna.Schumaker@Netapp.com>
>=20
> I received the following warning while running cthon against an ontap
> server running pNFS:
>=20
> [   57.202521] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> [   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-r=
eader section!!
> [   57.202527]
>                other info that might help us debug this:
>=20
> [   57.202528]
>                rcu_scheduler_active =3D 2, debug_locks =3D 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-g2cc14f=
52aeb7 #41492 5b09971b4965c0aceba19f3eea324a4a806e227e
> [   57.202534] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS u=
nknown 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 ebe02571b9a8=
ceebf7d98e71675af20c19bdb1f6]
> [   57.202596]  rpc_clnt_setup_test_and_add_xprt+0x50/0x180 [sunrpc ebe02=
571b9a8ceebf7d98e71675af20c19bdb1f6]
> [   57.202621]  ? rpc_clnt_add_xprt+0x254/0x300 [sunrpc ebe02571b9a8ceebf=
7d98e71675af20c19bdb1f6]
> [   57.202646]  rpc_clnt_add_xprt+0x27a/0x300 [sunrpc ebe02571b9a8ceebf7d=
98e71675af20c19bdb1f6]
> [   57.202671]  ? __pfx_rpc_clnt_setup_test_and_add_xprt+0x10/0x10 [sunrp=
c ebe02571b9a8ceebf7d98e71675af20c19bdb1f6]
> [   57.202696]  nfs4_pnfs_ds_connect+0x345/0x760 [nfsv4 c716d88496ded0ea6=
d289bbea684fa996f9b57a9]
> [   57.202728]  ? __pfx_nfs4_test_session_trunk+0x10/0x10 [nfsv4 c716d884=
96ded0ea6d289bbea684fa996f9b57a9]
> [   57.202754]  nfs4_fl_prepare_ds+0x75/0xc0 [nfs_layout_nfsv41_files e3a=
4187f18ae8a27b630f9feae6831b584a9360a]
> [   57.202760]  filelayout_write_pagelist+0x4a/0x200 [nfs_layout_nfsv41_f=
iles e3a4187f18ae8a27b630f9feae6831b584a9360a]
> [   57.202765]  pnfs_generic_pg_writepages+0xbe/0x230 [nfsv4 c716d88496de=
d0ea6d289bbea684fa996f9b57a9]
> [   57.202788]  __nfs_pageio_add_request+0x3fd/0x520 [nfs 6c976fa593a7c29=
76f5a0aeb4965514a828e6902]
> [   57.202813]  nfs_pageio_add_request+0x18b/0x390 [nfs 6c976fa593a7c2976=
f5a0aeb4965514a828e6902]
> [   57.202831]  nfs_do_writepage+0x116/0x1e0 [nfs 6c976fa593a7c2976f5a0ae=
b4965514a828e6902]
> [   57.202849]  nfs_writepages_callback+0x13/0x30 [nfs 6c976fa593a7c2976f=
5a0aeb4965514a828e6902]
> [   57.202866]  write_cache_pages+0x265/0x450
> [   57.202870]  ? __pfx_nfs_writepages_callback+0x10/0x10 [nfs 6c976fa593=
a7c2976f5a0aeb4965514a828e6902]
> [   57.202891]  nfs_writepages+0x141/0x230 [nfs 6c976fa593a7c2976f5a0aeb4=
965514a828e6902]
> [   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 6c976fa593a7c2976f5a0aeb496551=
4a828e6902]
> [   57.202947]  nfs4_file_flush+0x72/0xb0 [nfsv4 c716d88496ded0ea6d289bbe=
a684fa996f9b57a9]
> [   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 0=
0 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: 0000=
000000000003
> [   57.202989] RAX: ffffffffffffffda RBX: 00007ffe857dfd68 RCX: 00007fe2b=
12e4a94
> [   57.202991] RDX: 0000000000002000 RSI: 00007ffe857ddc40 RDI: 000000000=
0000003
> [   57.202992] RBP: 00007ffe857dfc50 R08: 7fffffffffffffff R09: 000000006=
5650f49
> [   57.202993] R10: 00007fe2b11f8300 R11: 0000000000000202 R12: 000000000=
0000000
> [   57.202994] R13: 00007ffe857dfd80 R14: 00007fe2b1445000 R15: 000000000=
0000000
> [   57.202999]  </TASK>
>=20
> 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.
>=20
> Reviewed-by: Jeff Layton <jlayton@kernel.org>
> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
> ---
> v2: Don't provide a function bypass to skip taking the rcu_read_lock()
> ---
>  net/sunrpc/xprtmultipath.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
>=20
> diff --git a/net/sunrpc/xprtmultipath.c b/net/sunrpc/xprtmultipath.c
> index 701250b305db..0706575d9392 100644
> --- a/net/sunrpc/xprtmultipath.c
> +++ b/net/sunrpc/xprtmultipath.c
> @@ -336,8 +336,9 @@ struct rpc_xprt *xprt_iter_current_entry_offline(stru=
ct rpc_xprt_iter *xpi)
>  			xprt_switch_find_current_entry_offline);
>  }
> =20
> -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;
>  }
> =20
> +bool rpc_xprt_switch_has_addr(struct rpc_xprt_switch *xps,
> +			      const struct sockaddr *sap)
> +{
> +	bool res;
> +
> +	rcu_read_lock();
> +	res =3D __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)

Reviewed-by: Jeff Layton <jlayton@kernel.org>