linux-kernel - Re: [PATCH] mm,swapops: Update check in is_pfn_swap

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Message-ID: <ZhKmAecilbb2oSD9@localhost.localdomain>
Date: Sun, 7 Apr 2024 15:56:17 +0200
From: Oscar Salvador <osalvador@...e.de>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Miaohe Lin <linmiaohe@...wei.com>,
	David Hildenbrand <david@...hat.com>, Peter Xu <peterx@...hat.com>,
	stable@...r.kernel.org, Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH] mm,swapops: Update check in is_pfn_swap_entry for
 hwpoison entries

On Sun, Apr 07, 2024 at 03:05:37PM +0200, Oscar Salvador wrote:
> Tony reported that the Machine check recovery was broken in v6.9-rc1,
> as he was hitting a VM_BUG_ON when injecting uncorrectable memory errors
> to DRAM.
> After some more digging and debugging on his side, he realized that this
> went back to v6.1, with the introduction of 'commit 0d206b5d2e0d ("mm/swap: add
> swp_offset_pfn() to fetch PFN from swap entry")'.
> That commit, among other things, introduced swp_offset_pfn(), replacing
> hwpoison_entry_to_pfn() in its favour.
> 
> The patch also introduced a VM_BUG_ON() check for is_pfn_swap_entry(),
> but is_pfn_swap_entry() never got updated to cover hwpoison entries, which
> means that we would hit the VM_BUG_ON whenever we would call
> swp_offset_pfn() for such entries on environments with CONFIG_DEBUG_VM set.
> Fix this by updating the check to cover hwpoison entries as well, and update
> the comment while we are it.
> 
> Reported-by: Tony Luck <tony.luck@...el.com>
> Closes: https://lore.kernel.org/all/Zg8kLSl2yAlA3o5D@agluck-desk3/
> Tested-by: Tony Luck <tony.luck@...el.com>
> Fixes: 0d206b5d2e0d ("mm/swap: add swp_offset_pfn() to fetch PFN from swap entry")
> Cc: <stable@...r.kernel.org> # 6.1.x

I think I need to clarify why the stable.

It is my understanding that some distros ship their kernel with
CONFIG_DEBUG_VM set by default (I think Fedora comes to my mind?).
I am fine with backing down if people think that this is an
overreaction.


-- 
Oscar Salvador
SUSE Labs