linux-kernel - Re: [PATCH] Revert "nios2: Convert __pte_free

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Message-ID: <d83eb041-258a-c0ba-69cd-e544dda9d22f@roeck-us.net>
Date:   Wed, 28 Jun 2023 06:01:47 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Dinh Nguyen <dinguyen@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Shuah Khan <shuah@...nel.org>
Cc:     linux-kernel@...r.kernel.org, vishal.moola@...il.com,
        akpm@...ux-foundation.org, sfr@...b.auug.org.au
Subject: Re: [PATCH] Revert "nios2: Convert __pte_free_tlb() to use ptdescs"

On 6/27/23 16:23, Guenter Roeck wrote:
> On 6/27/23 15:35, Linus Torvalds wrote:
>> On Tue, 27 Jun 2023 at 15:14, Dinh Nguyen <dinguyen@...nel.org> wrote:
>>>
>>> This reverts commit 6ebe94baa2b9ddf3ccbb7f94df6ab26234532734.
>>>
>>> The patch "nios2: Convert __pte_free_tlb() to use ptdescs" was supposed
>>> to go together with a patchset that Vishal Moola had planned taking it
>>> through the mm tree. By just having this patch, all NIOS2 builds are
>>> broken.
>>
>> This is now at least the third time just this merge window where some
>> base tree was broken, and people thought that linux-next is some kind
>> of testing ground for it all.
>>
>> NO!
>>
>> Linux-next is indeed for testing, and for finding situations where
>> there are interactions between different trees.
>>
>> But linux-next is *not* a replacement for "this tree has to work on
>> its own". THAT testing needs to be done independently, and *before* a
>> tree hits linux-next.
>>
>> It is *NOT* ok to say "this will work in combination with that other
>> tree". EVERY SINGLE TREE needs to work on its own, because otherwise
>> you cannot bisect the end result sanely.
>>
>> We apparently had the NIOS2 tree being broken. And the RCU tree was
>> broken. And the KUnit tree was broken.
>>
> 
> Actually, this one is broken in linux-next as well because it was pulled
> into it, but the context patches needed to make it work (compile) are not
> there. It is also broken in next/pending-fixes for the same reason.
> 
> Only this happened so quick that by the time I noticed and reported
> and argued that, no, I did not try to apply this patch on its own,
> the pull request into mainline was already sent and applied.
> 
> Problem with linux-next is that it is so badly broken that it would take
> a full-time position to track down all its failures. Then there are those
> last-minute patches added in the week (or days) before the commit window
> opens which break it again. This is one example, but there is at least
> one more in linux-next (and pending-fixes); see
> https://kerneltests.org/builders/next-sh-pending-fixes/builds/822/steps/buildcommand/logs/stdio
> 

And now the broken (never compiled) patch made it into mainline
and breaks the sh:dreamcast_defconfig build there.

Yes, it does happen a lot that builds are temporarily broken in mainline
because patch series are split up among maintainers and submitted to mainline
without regard of buildability. I have learned to live with that and don't
normally report it because I know (ok, hope) it is going to be fixed
by the end of the commit window.

I personally find patch series - typically doing some cleanup - which are
not even build tested on the affected architectures much more annoying.

Guenter