linux-kernel - Re: [PATCH v2 ratelimit 11/14] ratelimit: Force re-initialization when rate-limiting re-enabled

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Message-ID: <257c3b91-e30f-48be-9788-d27a4445a416@sirena.org.uk>
Date: Wed, 23 Apr 2025 16:59:49 +0100
From: Mark Brown <broonie@...nel.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: linux-kernel@...r.kernel.org, kernel-team@...a.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kuniyuki Iwashima <kuniyu@...zon.com>,
	Mateusz Guzik <mjguzik@...il.com>, Petr Mladek <pmladek@...e.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Jon Pan-Doh <pandoh@...gle.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Karolina Stolarek <karolina.stolarek@...cle.com>,
	Aishwarya.TCV@....com, sraithal@....com
Subject: Re: [PATCH v2 ratelimit 11/14] ratelimit: Force re-initialization
 when rate-limiting re-enabled

On Fri, Apr 18, 2025 at 10:13:56AM -0700, Paul E. McKenney wrote:
> Currently, rate limiting being disabled results in an immediate early
> return with no state changes.  This can result in false-positive drops
> when re-enabling rate limiting.  Therefore, mark the ratelimit_state
> structure "uninitialized" when rate limiting is disabled.

Today's -next is failing to boot a defconfig on a wide range of arm64
ACPI platforms.  One ACPI platform (Softiron) is still fine, and I've
not noticed any DT platforms having issues.  Output grinds to a halt
during boot shortly after userspace starts on affected systems:

[   23.334050] Freeing unused kernel memory: 11328K
[   23.355182] Run /init as init process
[   23.378221] NET: Registered PF_INET6 protocol family
[   23.396506] Segment Routing with IPv6
[   23.414054] In-situ OAM (IOAM) with IPv6

A bisect converges fairly smoothly on this patch in -next, which doesn't
look completely implausible for something that stops console output - I
didn't dig into it at all though.  I see that Sirkanth (CCed) seems to
have reported a similar issue though with a different SHA1 since he
noticed on yesterday's -next.

Bisect log:

git bisect start
# status: waiting for both good and bad commits
# bad: [6ac908f24cd7ddae52c496bbc888e97ee7b033ac] Add linux-next specific files for 20250423
git bisect bad 6ac908f24cd7ddae52c496bbc888e97ee7b033ac
# status: waiting for good commit(s), bad commit known
# good: [2a9308cbc987660dd54df7af2a8685d512d467d0] Merge branch 'for-linux-next-fixes' of https://gitlab.freedesktop.org/drm/misc/kernel.git
git bisect good 2a9308cbc987660dd54df7af2a8685d512d467d0
# good: [68123785b5b6b54698b92e534c2d42cbb39701c0] Merge branch 'drm-next' of https://gitlab.freedesktop.org/drm/kernel.git
git bisect good 68123785b5b6b54698b92e534c2d42cbb39701c0
# good: [99554718252d6f01036ac8e0b45bcfc16bf0e0ce] next-20250414/tip
git bisect good 99554718252d6f01036ac8e0b45bcfc16bf0e0ce
# bad: [d017479907b87ffbcfe908c7188f19722d3fdb46] Merge branch 'togreg' of git://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git
git bisect bad d017479907b87ffbcfe908c7188f19722d3fdb46
# bad: [379565a0c27c2b9c9e6df8cac66dd458a71a33b5] Merge branch 'driver-core-next' of git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-core.git
git bisect bad 379565a0c27c2b9c9e6df8cac66dd458a71a33b5
# good: [fd02aa45bda6d2f2fedcab70e828867332ef7e1c] Merge branch 'kvm-tdx-initial' into HEAD
git bisect good fd02aa45bda6d2f2fedcab70e828867332ef7e1c
# bad: [a46505d01338de4299d417ebe01b12060ebadce7] next-20250414/workqueues
git bisect bad a46505d01338de4299d417ebe01b12060ebadce7
# good: [5109fd27d5ade19fe5de22c746157c693878dde7] Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux.git
git bisect good 5109fd27d5ade19fe5de22c746157c693878dde7
# bad: [ad0c7a85f8b529154c99103d4daa0e86f4c14272] ratelimit: Avoid atomic decrement under lock if already rate-limited
git bisect bad ad0c7a85f8b529154c99103d4daa0e86f4c14272
# good: [945e63d4897045421a64f86cbd8194e0ff06dc41] ratelimit: Count misses due to lock contention
git bisect good 945e63d4897045421a64f86cbd8194e0ff06dc41
# good: [13fa70e052ddc778ecf70db21a07d97c2487da90] ratelimit: Allow zero ->burst to disable ratelimiting
git bisect good 13fa70e052ddc778ecf70db21a07d97c2487da90
# bad: [5d80e7bbfddda9369f301b484d621c45de8edf5f] ratelimit: Don't flush misses counter if RATELIMIT_MSG_ON_RELEASE
git bisect bad 5d80e7bbfddda9369f301b484d621c45de8edf5f
# bad: [c8943bdecfc76711f83241e21da9d4530f872f0d] ratelimit: Force re-initialization when rate-limiting re-enabled
git bisect bad c8943bdecfc76711f83241e21da9d4530f872f0d
# first bad commit: [c8943bdecfc76711f83241e21da9d4530f872f0d] ratelimit: Force re-initialization when rate-limiting re-enabled

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