linux-kernel - [Solved] Building kernels under 5.10 takes twice as long as under 4.19

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Message-ID: <f145bb8d-0dcd-bd7a-e80b-2f53dc3ce6d0@mailbox.org>
Date:   Fri, 19 Mar 2021 21:27:39 +0100
From:   Rainer Fiebig <jrf@...lbox.org>
To:     linux-kernel@...r.kernel.org
Subject: [Solved] Building kernels under 5.10 takes twice as long as under
 4.19

Bit the bullet, bisected v5.5..v5.6 and found this:

0ddad21d3e99c743a3aa473121dc5561679e26bb is the first bad commit
commit 0ddad21d3e99c743a3aa473121dc5561679e26bb
Author: Linus Torvalds <torvalds@...ux-foundation.org>
Date:   Mon Dec 9 09:48:27 2019 -0800

    pipe: use exclusive waits when reading or writing

[...]
[ Note! This kernel improvement seems to be very good at triggering a
race condition in the make jobserver (in GNU make 4.2.1) for me. It's a
long known bug that was fixed back in June 2017 by GNU make commit
b552b0525198 ("[SV 51159] Use a non-blocking read with pselect to
avoid hangs.").

But there wasn't a new release of GNU make until 4.3 on Jan 19 2020,
so a number of distributions may still have the buggy version. Some
have backported the fix to their 4.2.1 release, though, and even
without the fix it's quite timing-dependent whether the bug actually
is hit. ]
[...]

After updating "make" to 4.3 all is well.

Feynman was right again. ;)

-- 
The truth always turns out to be simpler than you thought.
Richard Feynman

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