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

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Date: Sun, 9 Jun 2024 10:25:30 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Thomas Gleixner <tglx@...utronix.de>
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, 09 Jun 2024 16:06:05 +0200
Thomas Gleixner <tglx@...utronix.de> wrote:

> On Sun, Jun 09 2024 at 09:04, Steven Rostedt wrote:
> > On Sun, 9 Jun 2024 14:33:01 +0800
> > Sam Sun <samsun1006219@...il.com> wrote:  
> >> [   82.310798][ T8020] ------------[ cut here ]------------
> >> [   82.311236][ T8020] kernel BUG at arch/x86/kernel/jump_label.c:73!  
> >
> > This is not a bug with jump labels. It's a bug with whatever is using jump
> > labels. Looks like something tried to modify a jump label that no longer
> > exists.  
> 
> The jump label exists.

Ah, I missed the set_attr_rdpmc() as something not with a "?" in front :-p

> 
> >> [   82.331873][ T8020]  set_attr_rdpmc+0x193/0x270
> >> [   82.332179][ T8020]  ? get_attr_rdpmc+0x30/0x30
> >> [   82.332511][ T8020]  ? sysfs_kf_write+0x18d/0x2b0
> >> [   82.332832][ T8020]  ? sysfs_kf_read+0x370/0x370
> >> [   82.333159][ T8020]  kernfs_fop_write_iter+0x3ab/0x500  
> >
> > So, something in kernfs modified a jump label location that was freed?  
> 
> No. What happens is:
> 
> 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?

-- Steve