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From: Peter Zijlstra <peterz@infradead.org>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: tglx@linutronix.de, mingo@redhat.com, dvhart@infradead.org,
	linux-kernel@vger.kernel.org, Davidlohr Bueso <dbueso@suse.de>
Subject: Re: [PATCH 2/2] futex: Leave the pi lock stealer in a consistent state upon successful fault
Date: Tue, 16 Mar 2021 21:12:32 +0100	[thread overview]
Message-ID: <YFERMIGd8hU9gm4F@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210316180305.sh7nyi4xjskd3e3j@offworld>

On Tue, Mar 16, 2021 at 11:03:05AM -0700, Davidlohr Bueso wrote:
> On Tue, 16 Mar 2021, Peter Zijlstra wrote:
> > 
> > IIRC we made the explicit choice to never loop here. That saves having
> > to worry about getting stuck in in-kernel loops.
> > 
> > Userspace triggering the case where the futex goes corrupt is UB, after
> > that we have no obligation for anything to still work. It's on them,
> > they get to deal with the bits remaining.
> 
> I was kind of expecting this answer, honestly. After all, we are warned
> about violations to the 10th:
> 
>  * [10] There is no transient state which leaves owner and user space
>  *      TID out of sync. Except one error case where the kernel is denied
>  *      write access to the user address, see fixup_pi_state_owner().
> 
> (btw, should we actually WARN_ON_ONCE this case such that the user is
> well aware things are screwed up?)

I'm not sure WARN is appropriate, it is something unpriv userspace
can trigger at will.

      parent reply	other threads:[~2021-03-16 20:13 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-15  5:02 [PATCH -tip 0/2] futex: Two pi fixes Davidlohr Bueso
2021-03-15  5:02 ` [PATCH 1/2] futex: Fix irq mismatch in exit_pi_state_list() Davidlohr Bueso
2021-03-15 13:12   ` Peter Zijlstra
2021-03-15 19:03     ` Davidlohr Bueso
2021-03-15  5:02 ` [PATCH 2/2] futex: Leave the pi lock stealer in a consistent state upon successful fault Davidlohr Bueso
2021-03-16 11:20   ` Peter Zijlstra
2021-03-16 18:03     ` Davidlohr Bueso
2021-03-16 19:48       ` Thomas Gleixner
2021-03-16 20:12       ` Peter Zijlstra [this message]

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