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@xxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20240618081336.3996825-1-chenhuacai@xxxxxxxxxxx
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;
