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Message-ID: <b67c9197-c519-4759-8813-4388428d88f3@p183>
Date: Thu, 10 Jul 2025 19:46:48 +0300
From: Alexey Dobriyan <adobriyan@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] mm: implement "memory.oops_if_bad_pte=1" boot option

On Wed, Jul 09, 2025 at 03:37:51PM -0700, Andrew Morton wrote:
> On Wed, 9 Jul 2025 21:10:59 +0300 Alexey Dobriyan <adobriyan@...il.com> wrote:
> 
> > Implement
> > 
> > 	memory.oops_if_bad_pte=1
> > 
> > boot option which oopses the machine instead of dreadful
> > 
> > 	BUG: Bad page map in process
> > 
> > message.
> > 
> > This is intended
> > for people who want to panic at the slightest provocation and
> > for people who ruled out hardware problems which in turn means that
> > delaying vmcore collection is counter-productive.
> > 
> > Linux doesn't (never?) panicked on PTE corruption and even implemented
> > ratelimited version of the message meaning it can go for minutes and
> > even hours without anyone noticing which is exactly the opposite of what
> > should be done to facilitate debugging.
> > 
> > Not enabled by default.
> > 
> > Not advertised.
> > 
> > @@ -490,6 +498,13 @@ static inline void add_mm_rss_vec(struct mm_struct *mm, int *rss)
> >  static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
> >  			  pte_t pte, struct page *page)
> >  {
> > +	/*
> > +	 * This line is a formality to collect vmcore ASAP. Real bug
> > +	 * (hardware or software) happened earlier, current registers and
> > +	 * backtrace aren't interesting.
> > +	 */
> > +	BUG_ON(oops_if_bad_pte);
> > +
> 
> Oh.  A pretty simple thing to do with bpf?

Unless you need to explain how to set it up on QA machines :^)
The good thing about boot options -- they are very easy to use.

> A script to tell the kernel
> "dump vmcore if you get here" would have applications in places other
> than print_bad_pte()?

Sure!

> That's what bpf_panic() was for (https://lwn.net/Articles/901284/) but
> it apparently didn't get merged for <reasons>.

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