netdev - Re: [PATCH net 4/4] tcp: various missing rcu_read_lock around __sk_dst

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Date:	Thu, 31 Mar 2016 18:19:52 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	sasha.levin@...cle.com, daniel@...earbox.net,
	alexei.starovoitov@...il.com, mkubecek@...e.cz
Subject: Re: [PATCH net 4/4] tcp: various missing rcu_read_lock around
 __sk_dst_get

On Fri, 2016-04-01 at 02:21 +0200, Hannes Frederic Sowa wrote:

> 
> [   31.064029] ===============================
> [   31.064030] [ INFO: suspicious RCU usage. ]
> [   31.064032] 4.5.0+ #13 Not tainted
> [   31.064033] -------------------------------
> [   31.064034] include/net/sock.h:1594 suspicious 
> rcu_dereference_check() usage!
> [   31.064035]
>                 other info that might help us debug this:
> 
> [   31.064041]
>                 rcu_scheduler_active = 1, debug_locks = 1
> [   31.064042] no locks held by ssh/817.
> [   31.064043]
>                 stack backtrace:
> [   31.064045] CPU: 0 PID: 817 Comm: ssh Not tainted 4.5.0+ #13
> [   31.064046] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), 
> BIOS 1.8.2-20150714_191134- 04/01/2014
> [   31.064047]  0000000000000286 000000006730b46b ffff8800badf7bd0 
> ffffffff81442b33
> [   31.064050]  ffff8800b8c78000 0000000000000001 ffff8800badf7c00 
> ffffffff8110ae75
> [   31.064052]  ffff880035ea2f00 ffff8800b8e28000 0000000000000003 
> 00000000000004c4
> [   31.064054] Call Trace:
> [   31.064058]  [<ffffffff81442b33>] dump_stack+0x85/0xc2
> [   31.064062]  [<ffffffff8110ae75>] lockdep_rcu_suspicious+0xc5/0x100
> [   31.064064]  [<ffffffff8173bf57>] __sk_dst_check+0x77/0xb0
> [   31.064066]  [<ffffffff8182e502>] inet6_sk_rebuild_header+0x52/0x300
> [   31.064068]  [<ffffffff813bb61e>] ? selinux_skb_peerlbl_sid+0x5e/0xa0
> [   31.064070]  [<ffffffff813bb69e>] ? 
> selinux_inet_conn_established+0x3e/0x40
> [   31.064072]  [<ffffffff817c2bad>] tcp_finish_connect+0x4d/0x270
> [   31.064074]  [<ffffffff817c33f7>] tcp_rcv_state_process+0x627/0xe40
> [   31.064076]  [<ffffffff81866584>] tcp_v6_do_rcv+0xd4/0x410
> [   31.064078]  [<ffffffff8173bc65>] release_sock+0x85/0x1c0
> [   31.064079]  [<ffffffff817e9983>] __inet_stream_connect+0x1c3/0x340
> [   31.064081]  [<ffffffff8173b089>] ? lock_sock_nested+0x49/0xb0
> [   31.064083]  [<ffffffff81100270>] ? abort_exclusive_wait+0xb0/0xb0
> [   31.064084]  [<ffffffff817e9b38>] inet_stream_connect+0x38/0x50
> [   31.064086]  [<ffffffff8173794f>] SYSC_connect+0xcf/0xf0
> [   31.064088]  [<ffffffff8110d069>] ? trace_hardirqs_on_caller+0x129/0x1b0
> [   31.064090]  [<ffffffff8100301b>] ? trace_hardirqs_on_thunk+0x1b/0x1d
> [   31.064091]  [<ffffffff8173854e>] SyS_connect+0xe/0x10
> [   31.064094]  [<ffffffff818a0e7c>] entry_SYSCALL_64_fastpath+0x1f/0xbd
> 
> Bye,
> Hannes

Thanks.

As you can see, release_sock() messes badly lockdep (once your other
patches are in )

Once we properly fix release_sock() and/or __release_sock(), all these
false positives disappear.