On 28.10.2020 12:43, Serge Belyshev wrote:
>
>> For several network drivers it was reported that using
>> __napi_schedule_irqoff() is unsafe with forced threading. One way to
>> fix this is switching back to __napi_schedule, but then we lose the
>> benefit of the irqoff version in general. As stated by Eric it doesn't
>> make sense to make the minimal hard irq handlers in drivers using NAPI
>> a thread. Therefore ensure that the hard irq handler is never
>> thread-ified.
>>
>> Fixes: 9a899a35b0d6 ("r8169: switch to napi_schedule_irqoff")
>> Link: https://lkml.org/lkml/2020/10/18/19
>> Signed-off-by: Heiner Kallweit <hkallwe...@gmail.com>
>> ---
>> drivers/net/ethernet/realtek/r8169_main.c | 8 ++++----
>> 1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/realtek/r8169_main.c
>> b/drivers/net/ethernet/realtek/r8169_main.c
>> index 7d366b036..3b6ddc706 100644
>> --- a/drivers/net/ethernet/realtek/r8169_main.c
>> +++ b/drivers/net/ethernet/realtek/r8169_main.c
> ...
>
> Hi! This patch actually breaks r8169 with threadirqs on an old box
> where it was working before:
>
> [ 0.000000] DMI: Gigabyte Technology Co., Ltd.
> GA-MA790FX-DQ6/GA-MA790FX-DQ6, BIOS F7g 07/19/2010
> ...
> [ 1.072676] r8169 0000:02:00.0 eth0: RTL8168b/8111b, 00:1a:4d:5d:6b:c3,
> XID 380, IRQ 18
> ...
> [ 8.850099] genirq: Flags mismatch irq 18. 00010080 (eth0) vs. 00002080
> (ahci[0000:05:00.0])
>
> (error is reported to userspace, interface failed to bring up).
> Reverting the patch fixes the problem.
>
Thanks for the report. On this old chip version MSI is unreliable,
therefore r8169 falls back to a PCI legacy interrupt. On your system
this PCI legacy interrupt seems to be shared between network and
disk. Then the IRQ core tries to threadify the disk interrupt
(setting IRQF_ONESHOT), whilst the network interrupt doesn't have
this flag set. This results in the flag mismatch error.
Maybe, if one source of a shared interrupt doesn't allow forced
threading, this should be applied to the other sources too.
But this would require a change in the IRQ core, therefore
+Thomas to get his opinion on the issue.
