Skip to content

wait: Fix __wait_event_hrtimeout for RT/DL tasks

Prarit Bhargava requested to merge prarit/centos-stream-9:2112265 into main

Bugzilla: https://bugzilla.redhat.com/2112265

commit cceeeb6a6d02e7b9a74ddd27a3225013b34174aa
Author: Juri Lelli juri.lelli@redhat.com
Date: Mon Jun 27 11:50:51 2022 +0200

wait: Fix __wait_event_hrtimeout for RT/DL tasks  

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.  

Reported-by: Bruno Goncalves <bgoncalv@redhat.com>  
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>  
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>  
Reviewed-by: Daniel Bristot de Oliveira <bristot@kernel.org>  
Reviewed-by: Valentin Schneider <vschneid@redhat.com>  
Link: https://lore.kernel.org/r/20220627095051.42470-1-juri.lelli@redhat.com

Signed-off-by: Prarit Bhargava prarit@redhat.com

Edited by Prarit Bhargava

Merge request reports