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percpu_test.c
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// SPDX-License-Identifier: GPL-2.0-only
#include <linux/limits.h>
#include <linux/module.h>
/* validate @native and @pcp counter values match @expected */
#define CHECK(native, pcp, expected) \
do { \
WARN((native) != (expected), \
"raw %ld (0x%lx) != expected %lld (0x%llx)", \
(native), (native), \
(long long)(expected), (long long)(expected)); \
WARN(__this_cpu_read(pcp) != (expected), \
"pcp %ld (0x%lx) != expected %lld (0x%llx)", \
__this_cpu_read(pcp), __this_cpu_read(pcp), \
(long long)(expected), (long long)(expected)); \
} while (0)
static DEFINE_PER_CPU(long, long_counter);
static DEFINE_PER_CPU(unsigned long, ulong_counter);
static int __init percpu_test_init(void)
{
/*
* volatile prevents compiler from optimizing it uses, otherwise the
* +ul_one/-ul_one below would replace with inc/dec instructions.
*/
volatile unsigned int ui_one = 1;
unsigned long long ull = 0;
unsigned long ul = 0;
long l = 0;
pr_info("percpu test start\n");
preempt_disable();
l += -1;
__this_cpu_add(long_counter, -1);
CHECK(l, long_counter, -1);
l += 1;
__this_cpu_add(long_counter, 1);
CHECK(l, long_counter, 0);
ul = 0;
__this_cpu_write(ulong_counter, 0);
ul += 1UL;
__this_cpu_add(ulong_counter, 1UL);
CHECK(ul, ulong_counter, 1);
ul += -1UL;
__this_cpu_add(ulong_counter, -1UL);
CHECK(ul, ulong_counter, 0);
ul += -(unsigned long)1;
__this_cpu_add(ulong_counter, -(unsigned long)1);
CHECK(ul, ulong_counter, -1);
ul = 0;
__this_cpu_write(ulong_counter, 0);
ul -= 1;
__this_cpu_dec(ulong_counter);
CHECK(ul, ulong_counter, -1);
CHECK(ul, ulong_counter, ULONG_MAX);
l += -ui_one;
__this_cpu_add(long_counter, -ui_one);
CHECK(l, long_counter, 0xffffffff);
l += ui_one;
__this_cpu_add(long_counter, ui_one);
CHECK(l, long_counter, (long)0x100000000LL);
l = 0;
__this_cpu_write(long_counter, 0);
l -= ui_one;
__this_cpu_sub(long_counter, ui_one);
CHECK(l, long_counter, -1);
l = 0;
__this_cpu_write(long_counter, 0);
l += ui_one;
__this_cpu_add(long_counter, ui_one);
CHECK(l, long_counter, 1);
l += -ui_one;
__this_cpu_add(long_counter, -ui_one);
CHECK(l, long_counter, (long)0x100000000LL);
l = 0;
__this_cpu_write(long_counter, 0);
l -= ui_one;
this_cpu_sub(long_counter, ui_one);
CHECK(l, long_counter, -1);
CHECK(l, long_counter, ULONG_MAX);
ul = 0;
__this_cpu_write(ulong_counter, 0);
ul += ui_one;
__this_cpu_add(ulong_counter, ui_one);
CHECK(ul, ulong_counter, 1);
ul = 0;
__this_cpu_write(ulong_counter, 0);
ul -= ui_one;
__this_cpu_sub(ulong_counter, ui_one);
CHECK(ul, ulong_counter, -1);
CHECK(ul, ulong_counter, ULONG_MAX);
ul = ull = 0;
__this_cpu_write(ulong_counter, 0);
ul = ull += UINT_MAX;
__this_cpu_add(ulong_counter, ull);
CHECK(ul, ulong_counter, UINT_MAX);
ul = 3;
__this_cpu_write(ulong_counter, 3);
ul = this_cpu_sub_return(ulong_counter, ui_one);
CHECK(ul, ulong_counter, 2);
ul = __this_cpu_sub_return(ulong_counter, ui_one);
CHECK(ul, ulong_counter, 1);
preempt_enable();
pr_info("percpu test done\n");
return -EAGAIN; /* Fail will directly unload the module */
}
static void __exit percpu_test_exit(void)
{
}
module_init(percpu_test_init)
module_exit(percpu_test_exit)
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Greg Thelen");
MODULE_DESCRIPTION("percpu operations test");