linux-kernel - Re: [PATCH v2] sched/rt: Fix race in push_rt

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Message-ID: <20250326131821.GA144611@pauld.westford.csb>
Date: Wed, 26 Mar 2025 09:18:21 -0400
From: Phil Auld <pauld@...hat.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Harshit Agarwal <harshit@...anix.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Jon Kohler <jon@...anix.com>,
	Gauri Patwardhan <gauri.patwardhan@...anix.com>,
	Rahul Chunduru <rahul.chunduru@...anix.com>,
	Will Ton <william.ton@...anix.com>
Subject: Re: [PATCH v2] sched/rt: Fix race in push_rt_task

On Mon, Feb 17, 2025 at 11:54:09AM -0500 Steven Rostedt wrote:
> On Fri, 14 Feb 2025 17:08:44 +0000
> Harshit Agarwal <harshit@...anix.com> wrote:
> 
> > Co-developed-by: Jon Kohler <jon@...anix.com>
> > Signed-off-by: Jon Kohler <jon@...anix.com>
> > Co-developed-by: Gauri Patwardhan <gauri.patwardhan@...anix.com>
> > Signed-off-by: Gauri Patwardhan <gauri.patwardhan@...anix.com>
> > Co-developed-by: Rahul Chunduru <rahul.chunduru@...anix.com>
> > Signed-off-by: Rahul Chunduru <rahul.chunduru@...anix.com>
> > Signed-off-by: Harshit Agarwal <harshit@...anix.com>
> > Tested-by: Will Ton <william.ton@...anix.com>
> > ---
> > Changes in v2:
> > - As per Steve's suggestion, removed some checks that are done after
> >   obtaining the lock that are no longer needed with the addition of new
> >   check.
> > - Moved up is_migration_disabled check.
> > - Link to v1:
> >   https://lore.kernel.org/lkml/20250211054646.23987-1-harshit@nutanix.com/
> > ---
> >  kernel/sched/rt.c | 54 +++++++++++++++++++++++------------------------
> >  1 file changed, 26 insertions(+), 28 deletions(-)
> 
> 
> Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>
>

We've got some cases that look to be hitting this as well.

I'm a little concerned about turning some runtime checks into
BUG_ON()s but in this case I think we are really just going to
trap out on !has_pushable_tasks() check first and if not, pick
a different task and don't drop the lock so it should pass the
BUG_ON()s and fail to match the original task.  So...

Reviewed-by: Phil Auld <pauld@...hat.com>



Cheers,
Phil

> Peter or Ingo,
> 
> Care to take his patch
> 
> Thanks,
> 
> -- Steve
> 

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