linux-kernel - Re: [Linux kernel bug] WARNING in static_key_slow_inc

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Date: Sun, 09 Jun 2024 18:02:49 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Sam Sun <samsun1006219@...il.com>, linux-kernel@...r.kernel.org,
 x86@...nel.org, syzkaller-bugs@...glegroups.com, peterz@...radead.org,
 jpoimboe@...nel.org, jbaron@...mai.com, ardb@...nel.org, mingo@...hat.com,
 Borislav Petkov <bp@...en8.de>, dave.hansen@...ux.intel.com,
 hpa@...or.com, xrivendell7@...il.com, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [Linux kernel bug] WARNING in static_key_slow_inc_cpuslocked

On Sun, Jun 09 2024 at 10:25, Steven Rostedt wrote:
> On Sun, 09 Jun 2024 16:06:05 +0200
> Thomas Gleixner <tglx@...utronix.de> wrote:
>> CPU 0                           	CPU 1
>> 
>> kernfs_fop_write_iter()			kernfs_fop_write_iter()
>>   set_attr_rdpmc()		  	  set_attr_rdpmc()
>>     arch_jump_label_transform_queue()       arch_jump_label_transform_queue()
>>      mutex_lock(text_mutex)                   mutex_lock(text_mutex)
>>      __jump_label_patch()
>>      text_poke_queue()
>>      mutex_unlokc(text_mutex)
>>                                               __jump_label_patch()
>> 
>> CPU 1 sees the original text and not the expected because CPU 0 did not
>> yet invoke arch_jump_label_transform_apply().
>> 
>> So clearly set_attr_rdpmc() lacks serialization, no?
>> 
> Hmm, but should jump labels fail when that happens? Or should it catch
> it, and not cause a BUG?

Well the bug is there to detect inconsistency and that clearly works :)

But I clearly can't read, because the jump label operations are
serialized via jump_label_mutex. Hrm...