Re: [Intel-wired-lan] [RFC iwl-net] e1000: Hold RTNL when e1000_down can be called

[Jacob Keller <jacob.e.keller@intel.com>]

On 10/22/2024 1:00 PM, Joe Damato wrote:
> On Tue, Oct 22, 2024 at 05:21:53PM +0000, Joe Damato wrote:
>> e1000_down calls netif_queue_set_napi, which assumes that RTNL is held.
>>
>> There are a few paths for e1000_down to be called in e1000 where RTNL is
>> not currently being held:
>>   - e1000_shutdown (pci shutdown)
>>   - e1000_suspend (power management)
>>   - e1000_reinit_locked (via e1000_reset_task delayed work)
>>
>> Hold RTNL in two places to fix this issue:
>>   - e1000_reset_task
>>   - __e1000_shutdown (which is called from both e1000_shutdown and
>>     e1000_suspend).
> 
> It looks like there's one other spot I missed:
> 
> e1000_io_error_detected (pci error handler) which should also hold
> rtnl_lock:
> 
> +       if (netif_running(netdev)) {
> +               rtnl_lock();
>                 e1000_down(adapter);
> +               rtnl_unlock();
> +       }
> 
> I can send that update in the v2, but I'll wait to see if Intel has suggestions
> on the below.
>  
>> The other paths which call e1000_down seemingly hold RTNL and are OK:
>>   - e1000_close (ndo_stop)
>>   - e1000_change_mtu (ndo_change_mtu)
>>
>> I'm submitting this is as an RFC because:
>>   - the e1000_reinit_locked issue appears very similar to commit
>>     21f857f0321d ("e1000e: add rtnl_lock() to e1000_reset_task"), which
>>     fixes a similar issue in e1000e
>>
>> however
>>
>>   - adding rtnl to e1000_reinit_locked seemingly conflicts with an
>>     earlier e1000 commit b2f963bfaeba ("e1000: fix lockdep warning in
>>     e1000_reset_task").
>>
>> Hopefully Intel can weigh in and shed some light on the correct way to
>> go.
>>

From my review, I think we need the RTNL lock around this function. The
deadlocks mentions in the fix lockdep patch appear to be due to having
an *extra* lock which could then cause issues.

>> Fixes: 8f7ff18a5ec7 ("e1000: Link NAPI instances to queues and IRQs")
>> Reported-by: Dmitry Antipov <dmantipov@yandex.ru>
>> Closes: https://lore.kernel.org/netdev/8cf62307-1965-46a0-a411-ff0080090ff9@yandex.ru/
>> Signed-off-by: Joe Damato <jdamato@fastly.com>