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Message-ID: <90124b02-76b5-d775-ac7d-a2e9d7677fa1@redhat.com>
Date:   Fri, 22 Apr 2022 10:23:50 -0400
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Subject: Re: [RFC 2/3] futex: exit: Print a warning when futex_cleanup fails
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To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Darren Hart <dvhart@infradead.org>,
        Davidlohr Bueso <dave@stgolabs.net>,
        =?UTF-8?Q?Andr=c3=a9_Almeida?= <andrealmeid@collabora.com>,
        Arjan van de Ven <arjan@infradead.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Matthew Wilcox <willy@infradead.org>
References: <20220421190533.1601879-1-npache@redhat.com>
 <20220421190533.1601879-3-npache@redhat.com> <87r15qrwdt.ffs@tglx>
From:   Nico Pache <npache@redhat.com>
In-Reply-To: <87r15qrwdt.ffs@tglx>
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On 4/21/22 16:53, Thomas Gleixner wrote:
> On Thu, Apr 21 2022 at 15:05, Nico Pache wrote:
> 
>> The futex_cleanup routines currently fails silently.
>>
>> Allow the futex_cleanup routines to fail more verbosely so we can
>> leave a message behind for easier debugging/error detecting.
> 
> This is a free ticket to spam dmesg for any unpriviledged user.
As Matthew pointed out, we'd want to rate limit this. I was also thinking we can
limit this to debug kernels so unpriviledged users can not cause dmesg spamming
in production configs.
> 
>> Fixes: 0771dfefc9e5 ("[PATCH] lightweight robust futexes: core")
> 
> There is nothing to fix, really.
Fair enough, its been part of the design since inceptions.
> 
> Robust futexes are best effort as I explained you before and spamming
> dmesg won't help anything.
It would have helped find the OOM/Robust Futex issue more quickly. It may also
help detect breakages in the pthread code (or any other users of robust futex)
if someone is doing something incorrectly.

Just a thought though. If you think its pointless to proceed down this path I
wont push forward.

Cheers,
-- Nico