On Wed, Nov 04 2020 at 12:17, Thomas Gleixner wrote:
> On Wed, Nov 04 2020 at 11:24, Thomas Gleixner wrote:
>> On Wed, Nov 04 2020 at 08:42, Mike Galbraith wrote:
>>> On Wed, 2020-11-04 at 01:56 +0100, Mike Galbraith wrote:
>>> --- a/kernel/futex.c
>>> +++ b/kernel/futex.c
>>> @@ -2383,7 +2383,18 @@ static int fixup_pi_state_owner(u32 __us
>>> * Since we just failed the trylock; there must be an owner.
>>> */
>>> newowner = rt_mutex_owner(&pi_state->pi_mutex);
>>> - BUG_ON(!newowner);
>>> +
>>> + /*
>>> + * Why? Because I know what I'm doing with these beasts? Nope,
>>> + * but what the hell, a busy restart loop let f_boosted become
>>> + * owner, so go for it. Box still boots, works, no longer makes
>>> + * boom with fbomb_v2, and as an added bonus, didn't even blow
>>> + * futextests all up. Maybe it'll help... or not, we'll see.
>>> + */
>>> + if (unlikely(!newowner)) {
>>> + err = -EAGAIN;
>>> + goto handle_err;
>>
>> Yes, that cures it, but does not really explain why newowner is
>> NULL. Lemme stare more.
>
> Aside of that it's going to create inconsistent state in the worst
> case. There is something really fishy in the trace Gratian provided....
Ok. With some more info added to the trace I could convince myself, that
Gratians trace is not so fishy at all and that Mike's fix is actually
the right thing to do.
I'll post that with a proper comment and changelog. Mike, can I add your
Signed-off-by to the thing?
