564cbc8793
For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
preference to ACCESS_ONCE(), and new code is expected to use one of the
former. So far, there's been no reason to change most existing uses of
ACCESS_ONCE(), as these aren't currently harmful.
However, for some features it is necessary to instrument reads and
writes separately, which is not possible with ACCESS_ONCE(). This
distinction is critical to correct operation.
The bulk of the kernel code can be transformed via Coccinelle to use
{READ,WRITE}_ONCE(), though this only modifies users of ACCESS_ONCE(),
and not the implementation itself. As such, it has the potential to
break homebrew ACCESS_ONCE() macros seen in some user code in the kernel
tree (e.g. the virtio code, as fixed in commit ea9156fb3b).
To avoid fragility if/when that transformation occurs, and to align with
the preferred usage of {READ,WRITE}_ONCE(), this patch updates the DSCR
selftest code to use READ_ONCE() rather than ACCESS_ONCE(). There should
be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: davem@davemloft.net
Cc: linux-arch@vger.kernel.org
Cc: snitzer@redhat.com
Cc: thor.thayer@linux.intel.com
Cc: tj@kernel.org
Cc: viro@zeniv.linux.org.uk
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1508792849-3115-11-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
128 lines
2.7 KiB
C
128 lines
2.7 KiB
C
/*
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* POWER Data Stream Control Register (DSCR) default test
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*
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* This test modifies the system wide default DSCR through
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* it's sysfs interface and then verifies that all threads
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* see the correct changed DSCR value immediately.
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*
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* Copyright 2012, Anton Blanchard, IBM Corporation.
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* Copyright 2015, Anshuman Khandual, IBM Corporation.
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 as published
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* by the Free Software Foundation.
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*/
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#include "dscr.h"
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static unsigned long dscr; /* System DSCR default */
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static unsigned long sequence;
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static unsigned long result[THREADS];
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static void *do_test(void *in)
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{
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unsigned long thread = (unsigned long)in;
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unsigned long i;
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for (i = 0; i < COUNT; i++) {
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unsigned long d, cur_dscr, cur_dscr_usr;
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unsigned long s1, s2;
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s1 = READ_ONCE(sequence);
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if (s1 & 1)
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continue;
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rmb();
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d = dscr;
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cur_dscr = get_dscr();
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cur_dscr_usr = get_dscr_usr();
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rmb();
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s2 = sequence;
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if (s1 != s2)
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continue;
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if (cur_dscr != d) {
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fprintf(stderr, "thread %ld kernel DSCR should be %ld "
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"but is %ld\n", thread, d, cur_dscr);
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result[thread] = 1;
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pthread_exit(&result[thread]);
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}
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if (cur_dscr_usr != d) {
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fprintf(stderr, "thread %ld user DSCR should be %ld "
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"but is %ld\n", thread, d, cur_dscr_usr);
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result[thread] = 1;
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pthread_exit(&result[thread]);
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}
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}
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result[thread] = 0;
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pthread_exit(&result[thread]);
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}
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int dscr_default(void)
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{
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pthread_t threads[THREADS];
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unsigned long i, *status[THREADS];
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unsigned long orig_dscr_default;
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orig_dscr_default = get_default_dscr();
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/* Initial DSCR default */
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dscr = 1;
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set_default_dscr(dscr);
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/* Spawn all testing threads */
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for (i = 0; i < THREADS; i++) {
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if (pthread_create(&threads[i], NULL, do_test, (void *)i)) {
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perror("pthread_create() failed");
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goto fail;
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}
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}
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srand(getpid());
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/* Keep changing the DSCR default */
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for (i = 0; i < COUNT; i++) {
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double ret = uniform_deviate(rand());
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if (ret < 0.0001) {
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sequence++;
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wmb();
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dscr++;
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if (dscr > DSCR_MAX)
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dscr = 0;
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set_default_dscr(dscr);
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wmb();
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sequence++;
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}
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}
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/* Individual testing thread exit status */
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for (i = 0; i < THREADS; i++) {
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if (pthread_join(threads[i], (void **)&(status[i]))) {
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perror("pthread_join() failed");
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goto fail;
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}
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if (*status[i]) {
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printf("%ldth thread failed to join with %ld status\n",
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i, *status[i]);
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goto fail;
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}
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}
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set_default_dscr(orig_dscr_default);
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return 0;
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fail:
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set_default_dscr(orig_dscr_default);
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return 1;
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}
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int main(int argc, char *argv[])
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{
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return test_harness(dscr_default, "dscr_default_test");
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}
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