linux-kernel - Re: [PATCH] sched_ext: Fix potential deadlock in destroy

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Message-ID: <20250117-defiant-tidy-foxhound-3bcbc2@leitao>
Date: Fri, 17 Jan 2025 01:46:12 -0800
From: Breno Leitao <leitao@...ian.org>
To: Tejun Heo <tj@...nel.org>
Cc: Andrea Righi <arighi@...dia.com>, David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, linux-kernel@...r.kernel.org,
	herbert@...dor.apana.org.au
Subject: Re: [PATCH] sched_ext: Fix potential deadlock in destroy_dsq()

Hello Tejun,

On Thu, Jan 16, 2025 at 04:06:26PM -1000, Tejun Heo wrote:
> On Thu, Jan 16, 2025 at 12:51:01PM +0100, Andrea Righi wrote:
> > When creating and destroying DSQs concurrently, a potential deadlock can
> > occur due to a circular locking dependency between the locks involved in
> > the operations:
> > 
> >  - create_dsq():
> > 
> >   rhashtable_bucket --> rq->lock --> dsq->lock
> 
> Hmm... this is probably the same thing that Breno tried to fix with
> rhashtable update. Breno, what's the current state of that patch? I saw bug
> reports and fix patch flying by but didn't track them closely.

Right, that seems exactly the problem I fixed. This is the current state
of the issue.

The fix is already in linux-next, but not on linus' tree:

	e1d3422c95f00  Breno Leitao        : rhashtable: Fix potential deadlock by moving schedule_work outside lock

That fixes caused a regression[1], and Herbert got a patch, which is not
committed in linux-next AFAIK.

This is Herbert's fix:

	https://lore.kernel.org/all/Z4XWx5X0doetOJni@gondor.apana.org.au/

[1] Link: https://lore.kernel.org/all/Z4DoFYQ3ytB-wS3-@gondor.apana.org.au/

--breno