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From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Steven Rostedt
 <rostedt@goodmis.org>, Sam Sun <samsun1006219@gmail.com>, x86@kernel.org,
 syzkaller-bugs@googlegroups.com, xrivendell7@gmail.com
Subject: Re: [patch 2/4] jump_label: Fix concurrency issues in
 static_key_slow_dec()
In-Reply-To: <20240610175756.GU8774@noisy.programming.kicks-ass.net>
References: <87bk49xf15.ffs@tglx> <20240610124258.109097511@linutronix.de>
 <20240610124406.422897838@linutronix.de>
 <20240610175756.GU8774@noisy.programming.kicks-ass.net>
Date: Mon, 10 Jun 2024 20:00:36 +0200
Message-ID: <87cyoowud7.ffs@tglx>
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On Mon, Jun 10 2024 at 19:57, Peter Zijlstra wrote:
> On Mon, Jun 10, 2024 at 02:46:36PM +0200, Thomas Gleixner wrote:
>
>> @@ -247,20 +247,25 @@ EXPORT_SYMBOL_GPL(static_key_disable);
>>  
>>  static bool static_key_slow_try_dec(struct static_key *key)
>>  {
>> +	int v;
>>  
>>  	/*
>> +	 * Go into the slow path if key::enabled is less than or equal than
>> +	 * one. One is valid to shut down the key, anything less than one
>> +	 * is an imbalance, which is handled at the call site.
>> +	 *
>> +	 * That includes the special case of '-1' which is set in
>> +	 * static_key_slow_inc_cpuslocked(), but that's harmless as it is
>> +	 * fully serialized in the slow path below. By the time this task
>> +	 * acquires the jump label lock the value is back to one and the
>> +	 * retry under the lock must succeed.
>
> Harmless yes, but it really should not happen to begin with. If this
> happens it means someone wants to disable a key that is in the middle of
> getting enabled for the first time.
>
> I'm tempted to want a WARN here instead. Hmm?

No strong opinion