After the reworking of "Parallel CPU bringup", the cmdline "nosmp" and
"maxcpus=0" is broken. Because these parameters make setup_max_cpus be
zero, and setup_max_cpus is the "max_cpus" of bringup_nonboot_cpus().
In this case, "if (!--ncpus)" will not be true in cpuhp_bringup_mask(),
and the result is all the possible cpus are brought up.
We can fix it by changing "if (!--ncpus)" to "if (!ncpus--)". But to
make logic more clear and save some cpu cycles, it is better to check
"max_cpus" in bringup_nonboot_cpus(), return early if it is zero.
Cc: stable@xxxxxxxxxxxxxxx
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>
---
kernel/cpu.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 563877d6c28b..200974a31de8 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;
--
2.43.0
