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author | Oleg Nesterov <oleg@redhat.com> | 2024-04-13 17:17:46 +0300 |
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committer | Ingo Molnar <mingo@kernel.org> | 2024-04-28 11:08:21 +0300 |
commit | 257bf89d84121280904800acd25cc2c444c717ae (patch) | |
tree | 77885bdc1eb9b3d3d7bd1b93de4c9fad7954102a /Documentation | |
parent | 5097cbcb38e6e0d2627c9dde1985e91d2c9f880e (diff) | |
download | linux-257bf89d84121280904800acd25cc2c444c717ae.tar.xz |
sched/isolation: Fix boot crash when maxcpus < first housekeeping CPU
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
Diffstat (limited to 'Documentation')
0 files changed, 0 insertions, 0 deletions