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powerpc/64s: Fix hash__change_memory_range preemption warning 

stop_machine_cpuslocked takes a mutex so it must be called in a
preemptible context, so it can't simply be fixed by disabling
preemption.

This is not a bug, because CPU hotplug is locked, so this processor will
call in to the stop machine function. So raw_smp_processor_id() could be
used. This leaves a small chance that this thread will be migrated to
another CPU, so the master work would be done by a CPU from a different
context. Better for test coverage to make that a common case by just
having the first CPU to call in become the master.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221013151647.1857994-2-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2022-10-14 01:16:46 +10:00 committed by Michael Ellerman
parent b9ef323ea1
commit 2b2095f3a6
1 changed files with 5 additions and 3 deletions
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8
arch/powerpc/mm/book3s64/hash_pgtable.c
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@ -404,7 +404,8 @@ EXPORT_SYMBOL_GPL(hash__has_transparent_hugepage);
struct change_memory_parms {
unsigned long start, end, newpp;
unsigned int step, nr_cpus, master_cpu;
unsigned int step, nr_cpus;
atomic_t master_cpu;
atomic_t cpu_counter;
};
@ -478,7 +479,8 @@ static int change_memory_range_fn(void *data)
{
struct change_memory_parms *parms = data;
if (parms->master_cpu != smp_processor_id())
// First CPU goes through, all others wait.
if (atomic_xchg(&parms->master_cpu, 1) == 1)
return chmem_secondary_loop(parms);
// Wait for all but one CPU (this one) to call-in
@ -516,7 +518,7 @@ static bool hash__change_memory_range(unsigned long start, unsigned long end,
chmem_parms.end = end;
chmem_parms.step = step;
chmem_parms.newpp = newpp;
chmem_parms.master_cpu = smp_processor_id();
atomic_set(&chmem_parms.master_cpu, 0);
cpus_read_lock();