On 2024-10-04, Petr Mladek <pmla...@suse.com> wrote:
> On Fri 2024-10-04 02:08:52, Breno Leitao wrote:
>> =====================================================
>> WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected
>> 6.12.0-rc1-kbuilder-virtme-00033-gd4ac164bde7a #50 Not tainted
>> -----------------------------------------------------
>> swapper/0/1 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
>> ff1100010a260518 (_xmit_ETHER#2){+.-.}-{2:2}, at: virtnet_poll_tx
>> (./include/linux/netdevice.h:4361 drivers/net/virtio_net.c:2969)
>>
>> and this task is already holding:
>> ffffffff86f2b5b8 (target_list_lock){....}-{2:2}, at: write_ext_msg
>> (drivers/net/netconsole.c:?)
>> which would create a new lock dependency:
>> (target_list_lock){....}-{2:2} -> (_xmit_ETHER#2){+.-.}-{2:2}
>>
>> but this new dependency connects a HARDIRQ-irq-safe lock:
>> (console_owner){-...}-{0:0}
...
>> to a HARDIRQ-irq-unsafe lock:
>> (_xmit_ETHER#2){+.-.}-{2:2}
...
>> other info that might help us debug this:
>>
>> Chain exists of:
>> console_owner --> target_list_lock --> _xmit_ETHER#2
>>
>> Possible interrupt unsafe locking scenario:
>>
>> CPU0 CPU1
>> ---- ----
>> lock(_xmit_ETHER#2);
>> local_irq_disable();
>> lock(console_owner);
>> lock(target_list_lock);
>> <Interrupt>
>> lock(console_owner);
I can trigger this lockdep splat on v6.11 as well.
It only requires a printk() call within any interrupt handler, sometime
after the netconsole is initialized and has had at least one run from
softirq context.
> My understanding is that the fix is to always take "_xmit_ETHER#2"
> lock with interrupts disabled.
That seems to be one possible solution. But maybe there is reasoning why
that should not be done. (??) Right now it is clearly a spinlock that is
being taken from both interrupt and softirq contexts and does not
disable interrupts.
I will check if there is some previous kernel release where this problem
does not exist.
John Ogness
