All of lore.kernel.org
 help / color / mirror / Atom feed
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]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YFERMIGd8hU9gm4F@hirez.programming.kicks-ass.net \
    --to=peterz@infradead.org \
    --cc=dave@stgolabs.net \
    --cc=dbueso@suse.de \
    --cc=dvhart@infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=tglx@linutronix.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.