From mboxrd@z Thu Jan  1 00:00:00 1970
From: Arjan van de Ven <arjan@infradead.org>
Subject: Re: 2.6.17-mm3 -- BUG: illegal lock usage -- illegal
	{softirq-on-W} -> {in-softirq-R} usage.
Date: Thu, 29 Jun 2006 21:42:34 +0200
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References: <a44ae5cd0606291201v659b4235sfa9941aa3b18e766@mail.gmail.com>
	 <20060629122608.440d474c.akpm@osdl.org>
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Cc: Miles Lane <miles.lane@gmail.com>, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org
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To: Andrew Morton <akpm@osdl.org>
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On Thu, 2006-06-29 at 12:26 -0700, Andrew Morton wrote:
> On Thu, 29 Jun 2006 12:01:06 -0700
> "Miles Lane" <miles.lane@gmail.com> wrote:
> 
> > [ BUG: illegal lock usage! ]
> > ----------------------------
> 
> This is claiming that we're taking sk->sk_dst_lock in a deadlockable manner.
> 
> > illegal {softirq-on-W} -> {in-softirq-R} usage.
> 
> It found someone doing write_lock(sk_dst_lock) with softirqs enabled, but
> someone else takes read_lock(dst_lock) inside softirqs.
> 
> > java_vm/4418 [HC0[0]:SC1[1]:HE1:SE0] takes:
> >  (&sk->sk_dst_lock){---?}, at: [<c119d0a9>] sk_dst_check+0x1b/0xe6
> > {softirq-on-W} state was registered at:
> >   [<c102d1c8>] lock_acquire+0x60/0x80
> >   [<c12012d7>] _write_lock+0x23/0x32
> >   [<c11ddbe7>] inet_bind+0x16c/0x1cc
> >   [<c119ae58>] sys_bind+0x61/0x80
> >   [<c119b465>] sys_socketcall+0x7d/0x186
> >   [<c1002d6d>] sysenter_past_esp+0x56/0x8d
> 
> 	inet_bind()
> 	->sk_dst_get
> 	  ->read_lock(&sk->sk_dst_lock)

actually write_lock() not read_lock()


> 
> > irq event stamp: 11052
> > hardirqs last  enabled at (11052): [<c105d454>] kmem_cache_alloc+0x89/0xa6
> > hardirqs last disabled at (11051): [<c105d405>] kmem_cache_alloc+0x3a/0xa6
> > softirqs last  enabled at (11040): [<c11a506d>] dev_queue_xmit+0x224/0x24b
> > softirqs last disabled at (11041): [<c1004a64>] do_softirq+0x58/0xbd
> > 
> > other info that might help us debug this:
> > 1 lock held by java_vm/4418:
> >  #0:  (af_family_keys + (sk)->sk_family#4){-+..}, at: [<f93c9281>]
> > tcp_v6_rcv+0x308/0x7b7 [ipv6]
> 
> 	softirq
> 	->ip6_dst_lookup
> 	  ->sk_dst_check
> 	    ->sk_dst_reset
> 	      ->write_lock(&sk->sk_dst_lock);

write_lock.. or read_lock() ? 

> 
> > stack backtrace:
> >  [<c1003502>] show_trace_log_lvl+0x54/0xfd
> >  [<c1003b6a>] show_trace+0xd/0x10
> >  [<c1003c0e>] dump_stack+0x19/0x1b
> >  [<c102b833>] print_usage_bug+0x1cc/0x1d9
> >  [<c102bd34>] mark_lock+0x193/0x360
> >  [<c102c94a>] __lock_acquire+0x3b7/0x970
> >  [<c102d1c8>] lock_acquire+0x60/0x80
> >  [<c12013eb>] _read_lock+0x23/0x32

backtrace says read lock to me ...
> >  [<c119d0a9>] sk_dst_check+0x1b/0xe6
> >  [<f93ae479>] ip6_dst_lookup+0x31/0x172 [ipv6]
> >  [<f93c7065>] tcp_v6_send_synack+0x10f/0x238 [ipv6]
> >  [<f93c7dc5>] tcp_v6_conn_request+0x281/0x2c7 [ipv6]
> >  [<c11cca33>] tcp_rcv_state_process+0x5d/0xbde


> So the allegation is that if a softirq runs sk_dst_reset() while
> process-context code is running sk_dst_set(), we'll do write_lock() while
> holding read_lock().  

hmm or...

we're doing a write_lock(), then an interrupt can happen that triggers
the softirq that triggers the read_lock(), which will deadlock because
we interrupted the writer...