The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 6ef8eb5125722c241fd60d7b0c872d5c2e5dd4ca # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024070154-legged-throwaway-bd6a@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

6ef8eb512572 ("cpu: Fix broken cmdline "nosmp" and "maxcpus=0"")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 6ef8eb5125722c241fd60d7b0c872d5c2e5dd4ca Mon Sep 17 00:00:00 2001 From: Huacai Chen chenhuacai@kernel.org Date: Tue, 18 Jun 2024 16:13:36 +0800 Subject: [PATCH] cpu: Fix broken cmdline "nosmp" and "maxcpus=0"

After the rework of "Parallel CPU bringup", the cmdline "nosmp" and "maxcpus=0" parameters are not working anymore. These parameters set setup_max_cpus to zero and that's handed to bringup_nonboot_cpus().

The code there does a decrement before checking for zero, which brings it into the negative space and brings up all CPUs.

Add a zero check at the beginning of the function to prevent this.

[ tglx: Massaged change log ]

Fixes: 18415f33e2ac4ab382 ("cpu/hotplug: Allow "parallel" bringup up to CPUHP_BP_KICK_AP_STATE") Fixes: 06c6796e0304234da6 ("cpu/hotplug: Fix off by one in cpuhp_bringup_mask()") Signed-off-by: Huacai Chen chenhuacai@loongson.cn Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20240618081336.3996825-1-chenhuacai@loongson.cn

diff --git a/kernel/cpu.c b/kernel/cpu.c index 74cfdb66a9bd..3d2bf1d50a0c 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -1859,6 +1859,9 @@ static inline bool cpuhp_bringup_cpus_parallel(unsigned int ncpus) { return fals

void __init bringup_nonboot_cpus(unsigned int max_cpus) { + if (!max_cpus) + return; + /* Try parallel bringup optimization if enabled */ if (cpuhp_bringup_cpus_parallel(max_cpus)) return;