Re: [RFC 2/3] futex: exit: Print a warning when futex_cleanup fails

From: Nico Pache <npache@redhat.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Darren Hart" <dvhart@infradead.org>,
	"Davidlohr Bueso" <dave@stgolabs.net>,
	"André Almeida" <andrealmeid@collabora.com>,
	"Arjan van de Ven" <arjan@infradead.org>,
	"Ulrich Drepper" <drepper@redhat.com>
Subject: Re: [RFC 2/3] futex: exit: Print a warning when futex_cleanup fails
Date: Fri, 22 Apr 2022 10:12:39 -0400	[thread overview]
Message-ID: <19b324a4-f69c-1624-fbc7-e178b7c31d81@redhat.com> (raw)
In-Reply-To: <YmGwzRIHFlKZk3Hm@casper.infradead.org>


On 4/21/22 15:30, Matthew Wilcox wrote:
> On Thu, Apr 21, 2022 at 03:05:32PM -0400, Nico Pache wrote:
>> @@ -1007,13 +1013,15 @@ static inline void exit_pi_state_list(struct task_struct *curr) { }
>>  static void futex_cleanup(struct task_struct *tsk)
>>  {
>>  	if (unlikely(tsk->robust_list)) {
>> -		exit_robust_list(tsk);
>> +		if (!exit_robust_list(tsk))
>> +			pr_info("futex: exit_robust_list failed");
> 
> Doesn't this allow a malicious user process to spam the kernel logs
> with messages?  There needs to be a ratelimit on this, at least.
Fair point, we'd need a ratelimited print if we want to continue forward with
this. Additionally we may want to limit this print to debug kernels, but thats
just a thought.

Thanks for the review :)
-- Nico