6.8-stable review patch. If anyone has any objections, please let me know.
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From: Oleg Nesterov oleg@redhat.com
[ Upstream commit 257bf89d84121280904800acd25cc2c444c717ae ]
housekeeping_setup() checks cpumask_intersects(present, online) to ensure that the kernel will have at least one housekeeping CPU after smp_init(), but this doesn't work if the maxcpus= kernel parameter limits the number of processors available after bootup.
For example, a kernel with "maxcpus=2 nohz_full=0-2" parameters crashes at boot time on a virtual machine with 4 CPUs.
Change housekeeping_setup() to use cpumask_first_and() and check that the returned CPU number is valid and less than setup_max_cpus.
Another corner case is "nohz_full=0" on a machine with a single CPU or with the maxcpus=1 kernel argument. In this case non_housekeeping_mask is empty and tick_nohz_full_setup() makes no sense. And indeed, the kernel hits the WARN_ON(tick_nohz_full_running) in tick_sched_do_timer().
And how should the kernel interpret the "nohz_full=" parameter? It should be silently ignored, but currently cpulist_parse() happily returns the empty cpumask and this leads to the same problem.
Change housekeeping_setup() to check cpumask_empty(non_housekeeping_mask) and do nothing in this case.
Signed-off-by: Oleg Nesterov oleg@redhat.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Ingo Molnar mingo@kernel.org Reviewed-by: Phil Auld pauld@redhat.com Acked-by: Frederic Weisbecker frederic@kernel.org Link: https://lore.kernel.org/r/20240413141746.GA10008@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/isolation.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c index 373d42c707bc5..82e2f7fc7c267 100644 --- a/kernel/sched/isolation.c +++ b/kernel/sched/isolation.c @@ -109,6 +109,7 @@ static void __init housekeeping_setup_type(enum hk_type type, static int __init housekeeping_setup(char *str, unsigned long flags) { cpumask_var_t non_housekeeping_mask, housekeeping_staging; + unsigned int first_cpu; int err = 0;
if ((flags & HK_FLAG_TICK) && !(housekeeping.flags & HK_FLAG_TICK)) { @@ -129,7 +130,8 @@ static int __init housekeeping_setup(char *str, unsigned long flags) cpumask_andnot(housekeeping_staging, cpu_possible_mask, non_housekeeping_mask);
- if (!cpumask_intersects(cpu_present_mask, housekeeping_staging)) { + first_cpu = cpumask_first_and(cpu_present_mask, housekeeping_staging); + if (first_cpu >= nr_cpu_ids || first_cpu >= setup_max_cpus) { __cpumask_set_cpu(smp_processor_id(), housekeeping_staging); __cpumask_clear_cpu(smp_processor_id(), non_housekeeping_mask); if (!housekeeping.flags) { @@ -138,6 +140,9 @@ static int __init housekeeping_setup(char *str, unsigned long flags) } }
+ if (cpumask_empty(non_housekeeping_mask)) + goto free_housekeeping_staging; + if (!housekeeping.flags) { /* First setup call ("nohz_full=" or "isolcpus=") */ enum hk_type type;