4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Linus Torvalds torvalds@linux-foundation.org
commit b5b1404d0815894de0690de8a1ab58269e56eae6 upstream.
This is purely a preparatory patch for upcoming changes during the 4.19 merge window.
We have a function called "boot_cpu_state_init()" that isn't really about the bootup cpu state: that is done much earlier by the similarly named "boot_cpu_init()" (note lack of "state" in name).
This function initializes some hotplug CPU state, and needs to run after the percpu data has been properly initialized. It even has a comment to that effect.
Except it _doesn't_ actually run after the percpu data has been properly initialized. On x86 it happens to do that, but on at least arm and arm64, the percpu base pointers are initialized by the arch-specific 'smp_prepare_boot_cpu()' hook, which ran _after_ boot_cpu_state_init().
This had some unexpected results, and in particular we have a patch pending for the merge window that did the obvious cleanup of using 'this_cpu_write()' in the cpu hotplug init code:
- per_cpu_ptr(&cpuhp_state, smp_processor_id())->state = CPUHP_ONLINE; + this_cpu_write(cpuhp_state.state, CPUHP_ONLINE);
which is obviously the right thing to do. Except because of the ordering issue, it actually failed miserably and unexpectedly on arm64.
So this just fixes the ordering, and changes the name of the function to be 'boot_cpu_hotplug_init()' to make it obvious that it's about cpu hotplug state, because the core CPU state was supposed to have already been done earlier.
Marked for stable, since the (not yet merged) patch that will show this problem is marked for stable.
Reported-by: Vlastimil Babka vbabka@suse.cz Reported-by: Mian Yousaf Kaukab yousaf.kaukab@suse.com Suggested-by: Catalin Marinas catalin.marinas@arm.com Acked-by: Thomas Gleixner tglx@linutronix.de Cc: Will Deacon will.deacon@arm.com Cc: stable@kernel.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- include/linux/cpu.h | 2 +- init/main.c | 2 +- kernel/cpu.c | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-)
--- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -29,7 +29,7 @@ struct cpu { };
extern void boot_cpu_init(void); -extern void boot_cpu_state_init(void); +extern void boot_cpu_hotplug_init(void);
extern int register_cpu(struct cpu *cpu, int num); extern struct device *get_cpu_device(unsigned cpu); --- a/init/main.c +++ b/init/main.c @@ -509,8 +509,8 @@ asmlinkage __visible void __init start_k setup_command_line(command_line); setup_nr_cpu_ids(); setup_per_cpu_areas(); - boot_cpu_state_init(); smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */ + boot_cpu_hotplug_init();
build_all_zonelists(NULL, NULL); page_alloc_init(); --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -1944,7 +1944,7 @@ void __init boot_cpu_init(void) /* * Must be called _AFTER_ setting up the per_cpu areas */ -void __init boot_cpu_state_init(void) +void __init boot_cpu_hotplug_init(void) { per_cpu_ptr(&cpuhp_state, smp_processor_id())->state = CPUHP_ONLINE; }