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From: Thomas Gleixner <tglx@linutronix.de>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Sam Sun <samsun1006219@gmail.com>, linux-kernel@vger.kernel.org,
 x86@kernel.org, syzkaller-bugs@googlegroups.com, peterz@infradead.org,
 jpoimboe@kernel.org, jbaron@akamai.com, ardb@kernel.org, mingo@redhat.com,
 Borislav Petkov <bp@alien8.de>, dave.hansen@linux.intel.com,
 hpa@zytor.com, xrivendell7@gmail.com, Greg Kroah-Hartman
 <gregkh@linuxfoundation.org>, Tejun Heo <tj@kernel.org>
Subject: Re: [Linux kernel bug] WARNING in static_key_slow_inc_cpuslocked
In-Reply-To: <20240609102530.0a292b07@rorschach.local.home>
References: <20240609090431.3af238bc@gandalf.local.home>
 <87o78axlbm.ffs@tglx> <20240609102530.0a292b07@rorschach.local.home>
Date: Sun, 09 Jun 2024 18:02:49 +0200
Message-ID: <87le3exfx2.ffs@tglx>
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On Sun, Jun 09 2024 at 10:25, Steven Rostedt wrote:
> On Sun, 09 Jun 2024 16:06:05 +0200
> Thomas Gleixner <tglx@linutronix.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...