linux-kernel - Re: [PATCH 0/3] page table check default to warn instead of panic

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Message-Id: <20220912132322.7c486c40c6acf8eec0785c87@linux-foundation.org>
Date:   Mon, 12 Sep 2022 13:23:22 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Pasha Tatashin <pasha.tatashin@...een.com>
Cc:     corbet@....net, linux-mm@...ck.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, rick.p.edgecombe@...el.com
Subject: Re: [PATCH 0/3] page table check default to warn instead of panic

On Sun, 11 Sep 2022 09:59:20 +0000 Pasha Tatashin <pasha.tatashin@...een.com> wrote:

> From: Pasha Tatashin <tatashin@...gle.com>
> 
> Page table check when detects errors panics the kernel. Let instead,
> print a warning, and panic only when specifically requested via kernel
> parameter:
> 
> 	page_table_check=panic
> 
> The discussion about using panic vs. warn is here:
> https://lore.kernel.org/linux-mm/20220902232732.12358-1-rick.p.edgecombe@intel.com

The changelog doesn't actually describe the reason for making this
change.  Somebody obviously wants pagetable check errors to no longer
panic the kernel, but why??  (The same can be said of the [2/3]
changelog).

Also, should we be changing the default?  People who like the panic
will get a big surprise when they find out that they should have added
a kernel parameter to get the old behaviour back.  It would be less
disruptive to default to panic unless page_table_check=warn was added.

If there's a solid reason for changing the default, it should be
changelogged.  And if that reason is generally agreed to, perhaps the
kernel should print a warning at boot if neither page_table_check=panic
nor page_table_check=warn were provided.  To tell people that the
default has been changed.