netdev - Re: Urgent Bug Report Kernel crash 6.5.2

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Date: Fri, 08 Dec 2023 23:20:00 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Martin Zaharinov <micron10@...il.com>, peterz@...radead.org
Cc: netdev <netdev@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>,
 patchwork-bot+netdevbpf@...nel.org, Jakub Kicinski <kuba@...nel.org>,
 Stephen Hemminger <stephen@...workplumber.org>, kuba+netdrv@...nel.org,
 dsahern@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: Re: Urgent Bug Report Kernel crash 6.5.2

On Thu, Dec 07 2023 at 00:38, Martin Zaharinov wrote:
>> On 7 Dec 2023, at 0:26, Martin Zaharinov <micron10@...il.com> wrote:
>> 
>> in this line is : 
>> 
>> 
>>        /*
>>         * If the reference count was already in the dead zone, then this
>>         * put() operation is imbalanced. Warn, put the reference count back to
>>         * DEAD and tell the caller to not deconstruct the object.
>>         */
>>        if (WARN_ONCE(cnt >= RCUREF_RELEASED, "rcuref - imbalanced put()")) {
>>                atomic_set(&ref->refcnt, RCUREF_DEAD);
>>                return false;
>>        }

So a rcuref_put() operation triggers the warning because the reference
count is already dead, which means the rcuref_put() operation is
imbalanced.

>> [529520.875413] CPU: 13 PID: 0 Comm: swapper/13 Tainted: G           O       6.6.3 #1

Can you reproduce this without the Out of Tree module?

>> [529520.875653] RIP: 0010:rcuref_put_slowpath+0x5f/0x70
>> [529520.878136]  dst_release+0x1c/0x40
>> [529520.878229]  __dev_queue_xmit+0x594/0xcd0
>> [529520.878324]  ? eth_header+0x25/0xc0
>> [529520.878417]  ip_finish_output2+0x1a0/0x530
>> [529520.878514]  process_backlog+0x107/0x210
>> [529520.878610]  __napi_poll+0x20/0x180
>> [529520.878702]  net_rx_action+0x29f/0x380
>> [529520.878935]  __do_softirq+0xd0/0x202
>> [529520.879033]  do_softirq+0x3a/0x50

So this is one call chain triggering the issue...

>>> report same problem with kernel 6.6.1 - i think problem is in rcu
>>> but … if have options to add people from RCU here.

That's definitely not a RCU problem. It's a simple refcount fail.

Thanks,

        tglx