Re: suspicious RCU usage in xfrm_net_init()

On Thu, Aug 16, 2012 at 9:07 PM, Fan Du [off-list ref] wrote:

On 2012年08月16日 23:19, Fengguang Wu wrote:

quoted

Hi Fan,

On Thu, Aug 16, 2012 at 05:36:35PM +0800, Fan Du wrote:

quoted

Hi, Fengguang

Could you please try the below patch, see if spewing still there?
thanks

Yes, it worked, thank you very much!

Hi, Dave

Could you please pick up this patch?

Please do not make extra work for maintainers by sending attachments,
or requests for status/merge etc.  Your 1st patch had to be manually
set to an RFC, and now you add another patch less than 24h later.

Please see:

  http://patchwork.ozlabs.org/patch/177934/
  http://patchwork.ozlabs.org/patch/178132/

Also, a patch should describe the problem it solves (i.e. the symptom
the end user sees), and how the problem originated, and why the fix
in the patch is the _right_ fix.  The worst description a commit log
can have is one that just describes the C change in words, since
most people can read C on their own.

Here you add "_bh" in the code and then repeat exactly that in
the commit log.  Your commit log does not tell me when it broke,
or why it broke, or who had their use case broken.  Can you see
why this is not acceptable?

Please take the time to look at the traffic in netdev, and read
the feedback given by maintainers on other patches, so that the
common errors are understood by you, and not repeated.  It
will be time well spent!

Thanks,
Paul.
---

thanks

quoted

btw, your email client wraps long lines..

Oh, I will definitely fix this.
thanks feng guang for the testing :)

quoted

Thanks,
Fengguang

quoted

 From a3f86ecc3ee16ff81d49416bbf791780422988b3 Mon Sep 17 00:00:00 2001
From: Fan Du<redacted>
Date: Thu, 16 Aug 2012 17:31:25 +0800
Subject: [PATCH] Use rcu_dereference_bh to deference pointer
protected by rcu_read_lock_bh

Signed-off-by: Fan Du<redacted>
---
  net/xfrm/xfrm_policy.c |    2 +-
  1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 5ad4d2c..75a9d6a 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c

@@ -2501,7 +2501,7 @@ static void __net_init

xfrm_dst_ops_init(struct net *net)
        struct xfrm_policy_afinfo *afinfo;

        rcu_read_lock_bh();
-       afinfo = rcu_dereference(xfrm_policy_afinfo[AF_INET]);
+       afinfo = rcu_dereference_bh(xfrm_policy_afinfo[AF_INET]);
        if (afinfo)
                net->xfrm.xfrm4_dst_ops = *afinfo->dst_ops;
  #if IS_ENABLED(CONFIG_IPV6)
--
1.7.1




On 2012年08月16日 15:37, Fengguang Wu wrote:

quoted

Hi Priyanka,

The below warning shows up, probably related to this commit:

418a99ac6ad487dc9c42e6b0e85f941af56330f2 Replace rwlock on
xfrm_policy_afinfo with rcu

[    0.921216]
[    0.921645] ===============================
[    0.922766] [ INFO: suspicious RCU usage. ]
[    0.923887] 3.5.0-01540-g1669891 #64 Not tainted
[    0.925123] -------------------------------
[    0.932860] /c/kernel-tests/src/tip/net/xfrm/xfrm_policy.c:2504
suspicious rcu_dereference_check() usage!
[    0.935361]
[    0.935361] other info that might help us debug this:
[    0.935361]
[    0.937472]
[    0.937472] rcu_scheduler_active = 1, debug_locks = 0
[    0.939182] 2 locks held by swapper/1:
[    0.940171]  #0:  (net_mutex){+.+.+.}, at: [<ffffffff814e1ad0>]
register_pernet_subsys+0x21/0x57
[    0.942705]  #1:  (rcu_read_lock_bh){......}, at:
[<ffffffff822c7329>] xfrm_net_init+0x1e4/0x437
[    0.951507]
[    0.951507] stack backtrace:
[    0.952660] Pid: 1, comm: swapper Not tainted 3.5.0-01540-g1669891
#64
[    0.954364] Call Trace:
[    0.955074]  [<ffffffff8108b375>] lockdep_rcu_suspicious+0x174/0x187
[    0.956736]  [<ffffffff822c7453>] xfrm_net_init+0x30e/0x437
[    0.958205]  [<ffffffff822c7329>] ? xfrm_net_init+0x1e4/0x437
[    0.959712]  [<ffffffff814e134a>] ops_init+0x1bb/0x1ff
[    0.961067]  [<ffffffff810861f9>] ? trace_hardirqs_on+0x1b/0x24
[    0.962644]  [<ffffffff814e17cd>]
register_pernet_operations.isra.5+0x9d/0xfe
[    0.971376]  [<ffffffff814e1adf>] register_pernet_subsys+0x30/0x57
[    0.972992]  [<ffffffff822c7130>] xfrm_init+0x17/0x2c
[    0.974316]  [<ffffffff822c2f8c>] ip_rt_init+0x82/0xe7
[    0.975668]  [<ffffffff822c31dc>] ip_init+0x10/0x25
[    0.976952]  [<ffffffff822c3f77>] inet_init+0x235/0x360
[    0.978352]  [<ffffffff822c3d42>] ? devinet_init+0xf2/0xf2
[    0.979808]  [<ffffffff82283252>] do_one_initcall+0xb4/0x203
[    0.981313]  [<ffffffff8228354a>] kernel_init+0x1a9/0x29a
[    0.982732]  [<ffffffff822826d9>] ? loglevel+0x46/0x46
[    0.990889]  [<ffffffff816d3d84>] kernel_thread_helper+0x4/0x10
[    0.992472]  [<ffffffff816d262c>] ? retint_restore_args+0x13/0x13
[    0.994076]  [<ffffffff822833a1>] ? do_one_initcall+0x203/0x203
[    0.995636]  [<ffffffff816d3d80>] ? gs_change+0x13/0x13
[    0.997197] TCP established hash table entries: 8192 (order: 5,
131072 bytes)
[    1.000074] TCP bind hash table entries: 8192 (order: 7, 655360
bytes)

Thanks,
Fengguang

--

Love each day!
--fan

--

Love each day!
--fan