netdev - Re: ipv6/addrconf_dad_failure printk() in interrupt context

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Date:	Sun, 18 Dec 2011 10:15:08 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Marek Vasut <marek.vasut@...il.com>
Cc:	netdev@...r.kernel.org, Wolfgang Denk <wd@...x.de>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: ipv6/addrconf_dad_failure printk() in interrupt context

Le dimanche 18 décembre 2011 à 03:28 +0100, Marek Vasut a écrit :
> Hi,
> 
> I just recently hit the following issue. I might actually be wrong with my 
> conclusions so bear with me. The events that led to the issue:
> 
> 1) Duplicate IPv6 address on the network
> 2) console driver that locks a mutex when printk() is called

This seems buggy : printk() might be called from irq, so muext_lock() is
not allowed.

> 
> The problem is the following backtrace:
> 
> [    4.870000] eth0: IPv6 duplicate address XXXX::YYYY:ZZZZ:WWWW:0 detected!
> [    4.870000] ------------[ cut here ]------------
> [    4.870000] WARNING: at kernel/mutex.c:198 mutex_lock_nested+0x284/0x2c0()
> [    4.870000] Modules linked in:
> [    4.870000] [<c0013ab8>] (unwind_backtrace+0x0/0xf0) from [<c001d934>] 
> (warn_slowpath_common+0x4c/0x64)
> [    4.870000] [<c001d934>] (warn_slowpath_common+0x4c/0x64) from [<c001d968>] 
> (warn_slowpath_null+0x1c/0x24)
> [    4.870000] [<c001d968>] (warn_slowpath_null+0x1c/0x24) from [<c033a4f4>] 
> (mutex_lock_nested+0x284/0x2c0)
> [    4.870000] [<c033a4f4>] (mutex_lock_nested+0x284/0x2c0) from [<c0017d88>] 
> (clk_enable+0x20/0x48)
> [    4.870000] [<c0017d88>] (clk_enable+0x20/0x48) from [<c01dfbf0>] 
> (pl011_console_write+0x20/0x74)
> [    4.870000] [<c01dfbf0>] (pl011_console_write+0x20/0x74) from [<c001da98>] 
> (__call_console_drivers+0x7c/0x94)
> [    4.870000] [<c001da98>] (__call_console_drivers+0x7c/0x94) from [<c001df20>] 
> (console_unlock+0xf8/0x244)
> [    4.870000] [<c001df20>] (console_unlock+0xf8/0x244) from [<c001e308>] 
> (vprintk+0x29c/0x484)
> [    4.870000] [<c001e308>] (vprintk+0x29c/0x484) from [<c03355a8>] 
> (printk+0x20/0x30)
> [    4.870000] [<c03355a8>] (printk+0x20/0x30) from [<c02df600>] 
> (addrconf_dad_failure+0x148/0x158)
> [    4.870000] [<c02df600>] (addrconf_dad_failure+0x148/0x158) from [<c02ebde0>] 
> (ndisc_rcv+0xb38/0xdb0)
> [    4.870000] [<c02ebde0>] (ndisc_rcv+0xb38/0xdb0) from [<c02f1b28>] 
> (icmpv6_rcv+0x6ec/0x9c4)
> [    4.870000] [<c02f1b28>] (icmpv6_rcv+0x6ec/0x9c4) from [<c02da9a4>] 
> (ip6_input_finish+0x144/0x4e0)
> [    4.870000] [<c02da9a4>] (ip6_input_finish+0x144/0x4e0) from [<c02db424>] 
> (ip6_mc_input+0xb8/0x154)
> [    4.870000] [<c02db424>] (ip6_mc_input+0xb8/0x154) from [<c02db12c>] 
> (ipv6_rcv+0x300/0x53c)
> [    4.870000] [<c02db12c>] (ipv6_rcv+0x300/0x53c) from [<c0267b78>] 
> (__netif_receive_skb+0x240/0x420)
> [    4.870000] [<c0267b78>] (__netif_receive_skb+0x240/0x420) from [<c0267de8>] 
> (process_backlog+0x90/0x150)
> [    4.870000] [<c0267de8>] (process_backlog+0x90/0x150) from [<c026a5f8>] 
> (net_rx_action+0xc0/0x264)
> [    4.870000] [<c026a5f8>] (net_rx_action+0xc0/0x264) from [<c0023cfc>] 
> (__do_softirq+0xa8/0x214)
> [    4.870000] [<c0023cfc>] (__do_softirq+0xa8/0x214) from [<c00242c0>] 
> (irq_exit+0x8c/0x94)
> [    4.870000] [<c00242c0>] (irq_exit+0x8c/0x94) from [<c000f6d0>] 
> (handle_IRQ+0x34/0x84)
> [    4.870000] [<c000f6d0>] (handle_IRQ+0x34/0x84) from [<c000e5d8>] 
> (__irq_usr+0x38/0x80)
> [    4.870000] ---[ end trace 32eab6a8dcdca9c0 ]---
> 
> So basically what I see here is the following order of events:
> 
> Packet received -> IRQ generated -> ipv6 packet received (still in interrupt 
> context ... why not in tasklet ... or am I wrong here ?) -> icmpv6 packet 
> processing -> addrconf_dad_failure() called -> printk() called in there -> 
> mutex_lock() called in printk(), causing the warning.
> 
> Can printk() be actually called in interrupt context?
> 

Yes, it can be.

> What direction of solving this shall I take?
> 

Send this to lkml, since its not a netdev issue, but a kernel one.

> Thanks in advance!



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