Re: [PATCH] linux/wait: Fix __wait_event_hrtimeout for RT/DL tasks

[Daniel Bristot de Oliveira]

On 6/27/22 11:50, Juri Lelli wrote:
> Changes to hrtimer mode (potentially made by __hrtimer_init_sleeper on
> PREEMPT_RT) are not visible to hrtimer_start_range_ns, thus not
> accounted for by hrtimer_start_expires call paths. In particular,
> __wait_event_hrtimeout suffers from this problem as we have, for
> example:
> 
> fs/aio.c::read_events
>   wait_event_interruptible_hrtimeout
>     __wait_event_hrtimeout
>       hrtimer_init_sleeper_on_stack <- this might "mode |= HRTIMER_MODE_HARD"
>                                        on RT if task runs at RT/DL priority
>         hrtimer_start_range_ns
>           WARN_ON_ONCE(!(mode & HRTIMER_MODE_HARD) ^ !timer->is_hard)
>           fires since the latter doesn't see the change of mode done by
>           init_sleeper
> 
> Fix it by making __wait_event_hrtimeout call hrtimer_sleeper_start_expires,
> which is aware of the special RT/DL case, instead of hrtimer_start_range_ns.
> 
> Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Reported-by: Bruno Goncalves <bgoncalv@xxxxxxxxxx>
> Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>

Reviewed-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
-- Daniel