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@vger.kernel.org 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 --- 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;
The following commit has been merged into the smp/urgent branch of tip:
Commit-ID: 6ef8eb5125722c241fd60d7b0c872d5c2e5dd4ca Gitweb: https://git.kernel.org/tip/6ef8eb5125722c241fd60d7b0c872d5c2e5dd4ca Author: Huacai Chen chenhuacai@loongson.cn AuthorDate: Tue, 18 Jun 2024 16:13:36 +08:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Sun, 23 Jun 2024 20:04:14 +02:00
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
--- kernel/cpu.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/kernel/cpu.c b/kernel/cpu.c index 74cfdb6..3d2bf1d 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;
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