FAILED: patch "[PATCH] cpu: Fix broken cmdline "nosmp" and "maxcpus=0"" failed to apply to 6.6-stable tree

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 <[email protected]>.

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 '<[email protected]>' --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 <[email protected]>
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 ]

index 74cfdb66a9bd..3d2bf1d50a0c 100644
@@ -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;

From: Huacai Chen <[email protected]>

commit 6ef8eb5125722c241fd60d7b0c872d5c2e5dd4ca upstream.

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 ]

---
 kernel/cpu.c |    3 +++
 1 file changed, 3 insertions(+)

@@ -1907,6 +1907,9 @@ static inline bool cpuhp_bringup_cpus_pa
 
 void __init bringup_nonboot_cpus(unsigned int setup_max_cpus)
 {
+	if (!setup_max_cpus)
+		return;
+
 	/* Try parallel bringup optimization if enabled */
 	if (cpuhp_bringup_cpus_parallel(setup_max_cpus))
 		return;

Now queued up, thanks.

greg k-h