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mirror_zfs/module/splat/splat-mutex.c
Brian Behlendorf ede0bdffb6 Treat mutex->owner as volatile 
When HAVE_MUTEX_OWNER is defined and we are directly accessing
mutex->owner treat is as volative with the ACCESS_ONCE() helper.
Without this you may get a stale cached value when accessing it
from different cpus.  This can result in incorrect behavior from
mutex_owned() and mutex_owner().  This is not a problem for the
!HAVE_MUTEX_OWNER case because in this case all the accesses
are covered by a spin lock which similarly gaurentees we will
not be accessing stale data.

Secondly, check CONFIG_SMP before allowing access to mutex->owner.
I see that for non-SMP setups the kernel does not track the owner
so we cannot rely on it.

Thirdly, check CONFIG_MUTEX_DEBUG when this is defined and the
HAVE_MUTEX_OWNER is defined surprisingly the mutex->owner will
not be cleared on mutex_exit().  When this is the case the SPL
needs to make sure to do it to ensure MUTEX_HELD() behaves as
expected or you will certainly assert in mutex_destroy().

Finally, improve the mutex regression tests.  For mutex_owned() we
now minimally check that it behaves correctly when checked from the
owner thread or the non-owner thread.  This subtle behaviour has bit
me before and I'd like to catch it early next time if it reappears.

As for mutex_owned() regression test additonally verify that
mutex->owner is always cleared on mutex_exit().
2010-06-28 16:02:57 -07:00

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/*****************************************************************************\
* Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
* Copyright (C) 2007 The Regents of the University of California.
* Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
* Written by Brian Behlendorf <behlendorf1@llnl.gov>.
* UCRL-CODE-235197
*
* This file is part of the SPL, Solaris Porting Layer.
* For details, see <http://github.com/behlendorf/spl/>.
*
* The SPL is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* option) any later version.
*
* The SPL is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*
* You should have received a copy of the GNU General Public License along
* with the SPL. If not, see <http://www.gnu.org/licenses/>.
*****************************************************************************
* Solaris Porting LAyer Tests (SPLAT) Mutex Tests.
\*****************************************************************************/
#include "splat-internal.h"
#define SPLAT_MUTEX_NAME "mutex"
#define SPLAT_MUTEX_DESC "Kernel Mutex Tests"
#define SPLAT_MUTEX_TEST1_ID 0x0401
#define SPLAT_MUTEX_TEST1_NAME "tryenter"
#define SPLAT_MUTEX_TEST1_DESC "Validate mutex_tryenter() correctness"
#define SPLAT_MUTEX_TEST2_ID 0x0402
#define SPLAT_MUTEX_TEST2_NAME "race"
#define SPLAT_MUTEX_TEST2_DESC "Many threads entering/exiting the mutex"
#define SPLAT_MUTEX_TEST3_ID 0x0403
#define SPLAT_MUTEX_TEST3_NAME "owned"
#define SPLAT_MUTEX_TEST3_DESC "Validate mutex_owned() correctness"
#define SPLAT_MUTEX_TEST4_ID 0x0404
#define SPLAT_MUTEX_TEST4_NAME "owner"
#define SPLAT_MUTEX_TEST4_DESC "Validate mutex_owner() correctness"
#define SPLAT_MUTEX_TEST_MAGIC 0x115599DDUL
#define SPLAT_MUTEX_TEST_NAME "mutex_test"
#define SPLAT_MUTEX_TEST_TASKQ "mutex_taskq"
#define SPLAT_MUTEX_TEST_COUNT 128
typedef struct mutex_priv {
unsigned long mp_magic;
struct file *mp_file;
kmutex_t mp_mtx;
int mp_rc;
int mp_rc2;
} mutex_priv_t;
static void
splat_mutex_test1_func(void *arg)
{
mutex_priv_t *mp = (mutex_priv_t *)arg;
ASSERT(mp->mp_magic == SPLAT_MUTEX_TEST_MAGIC);
if (mutex_tryenter(&mp->mp_mtx)) {
mp->mp_rc = 0;
mutex_exit(&mp->mp_mtx);
} else {
mp->mp_rc = -EBUSY;
}
}
static int
splat_mutex_test1(struct file *file, void *arg)
{
mutex_priv_t *mp;
taskq_t *tq;
int id, rc = 0;
mp = (mutex_priv_t *)kmalloc(sizeof(*mp), GFP_KERNEL);
if (mp == NULL)
return -ENOMEM;
tq = taskq_create(SPLAT_MUTEX_TEST_TASKQ, 1, maxclsyspri,
50, INT_MAX, TASKQ_PREPOPULATE);
if (tq == NULL) {
rc = -ENOMEM;
goto out2;
}
mp->mp_magic = SPLAT_MUTEX_TEST_MAGIC;
mp->mp_file = file;
mutex_init(&mp->mp_mtx, SPLAT_MUTEX_TEST_NAME, MUTEX_DEFAULT, NULL);
mutex_enter(&mp->mp_mtx);
/*
* Schedule a task function which will try and acquire the mutex via
* mutex_tryenter() while it's held. This should fail and the task
* function will indicate this status in the passed private data.
*/
mp->mp_rc = -EINVAL;
id = taskq_dispatch(tq, splat_mutex_test1_func, mp, TQ_SLEEP);
if (id == 0) {
mutex_exit(&mp->mp_mtx);
splat_vprint(file, SPLAT_MUTEX_TEST1_NAME, "%s",
"taskq_dispatch() failed\n");
rc = -EINVAL;
goto out;
}
taskq_wait_id(tq, id);
mutex_exit(&mp->mp_mtx);
/* Task function successfully acquired mutex, very bad! */
if (mp->mp_rc != -EBUSY) {
splat_vprint(file, SPLAT_MUTEX_TEST1_NAME,
"mutex_trylock() incorrectly succeeded when "
"the mutex was held, %d/%d\n", id, mp->mp_rc);
rc = -EINVAL;
goto out;
} else {
splat_vprint(file, SPLAT_MUTEX_TEST1_NAME, "%s",
"mutex_trylock() correctly failed when "
"the mutex was held\n");
}
/*
* Schedule a task function which will try and acquire the mutex via
* mutex_tryenter() while it is not held. This should succeed and
* can be verified by checking the private data.
*/
mp->mp_rc = -EINVAL;
id = taskq_dispatch(tq, splat_mutex_test1_func, mp, TQ_SLEEP);
if (id == 0) {
splat_vprint(file, SPLAT_MUTEX_TEST1_NAME, "%s",
"taskq_dispatch() failed\n");
rc = -EINVAL;
goto out;
}
taskq_wait_id(tq, id);
/* Task function failed to acquire mutex, very bad! */
if (mp->mp_rc != 0) {
splat_vprint(file, SPLAT_MUTEX_TEST1_NAME,
"mutex_trylock() incorrectly failed when "
"the mutex was not held, %d/%d\n", id, mp->mp_rc);
rc = -EINVAL;
} else {
splat_vprint(file, SPLAT_MUTEX_TEST1_NAME, "%s",
"mutex_trylock() correctly succeeded "
"when the mutex was not held\n");
}
out:
taskq_destroy(tq);
mutex_destroy(&(mp->mp_mtx));
out2:
kfree(mp);
return rc;
}
static void
splat_mutex_test2_func(void *arg)
{
mutex_priv_t *mp = (mutex_priv_t *)arg;
int rc;
ASSERT(mp->mp_magic == SPLAT_MUTEX_TEST_MAGIC);
/* Read the value before sleeping and write it after we wake up to
* maximize the chance of a race if mutexs are not working properly */
mutex_enter(&mp->mp_mtx);
rc = mp->mp_rc;
set_current_state(TASK_INTERRUPTIBLE);
schedule_timeout(HZ / 100); /* 1/100 of a second */
VERIFY(mp->mp_rc == rc);
mp->mp_rc = rc + 1;
mutex_exit(&mp->mp_mtx);
}
static int
splat_mutex_test2(struct file *file, void *arg)
{
mutex_priv_t *mp;
taskq_t *tq;
int i, rc = 0;
mp = (mutex_priv_t *)kmalloc(sizeof(*mp), GFP_KERNEL);
if (mp == NULL)
return -ENOMEM;
/* Create several threads allowing tasks to race with each other */
tq = taskq_create(SPLAT_MUTEX_TEST_TASKQ, num_online_cpus(),
maxclsyspri, 50, INT_MAX, TASKQ_PREPOPULATE);
if (tq == NULL) {
rc = -ENOMEM;
goto out;
}
mp->mp_magic = SPLAT_MUTEX_TEST_MAGIC;
mp->mp_file = file;
mutex_init(&(mp->mp_mtx), SPLAT_MUTEX_TEST_NAME, MUTEX_DEFAULT, NULL);
mp->mp_rc = 0;
/*
* Schedule N work items to the work queue each of which enters the
* mutex, sleeps briefly, then exits the mutex. On a multiprocessor
* box these work items will be handled by all available CPUs. The
* task function checks to ensure the tracked shared variable is
* always only incremented by one. Additionally, the mutex itself
* is instrumented such that if any two processors are in the
* critical region at the same time the system will panic. If the
* mutex is implemented right this will never happy, that's a pass.
*/
for (i = 0; i < SPLAT_MUTEX_TEST_COUNT; i++) {
if (!taskq_dispatch(tq, splat_mutex_test2_func, mp, TQ_SLEEP)) {
splat_vprint(file, SPLAT_MUTEX_TEST2_NAME,
"Failed to queue task %d\n", i);
rc = -EINVAL;
}
}
taskq_wait(tq);
if (mp->mp_rc == SPLAT_MUTEX_TEST_COUNT) {
splat_vprint(file, SPLAT_MUTEX_TEST2_NAME, "%d racing threads "
"correctly entered/exited the mutex %d times\n",
num_online_cpus(), mp->mp_rc);
} else {
splat_vprint(file, SPLAT_MUTEX_TEST2_NAME, "%d racing threads "
"only processed %d/%d mutex work items\n",
num_online_cpus(),mp->mp_rc,SPLAT_MUTEX_TEST_COUNT);
rc = -EINVAL;
}
taskq_destroy(tq);
mutex_destroy(&(mp->mp_mtx));
out:
kfree(mp);
return rc;
}
static void
splat_mutex_owned(void *priv)
{
mutex_priv_t *mp = (mutex_priv_t *)priv;
ASSERT(mp->mp_magic == SPLAT_MUTEX_TEST_MAGIC);
mp->mp_rc = mutex_owned(&mp->mp_mtx);
mp->mp_rc2 = MUTEX_HELD(&mp->mp_mtx);
}
static int
splat_mutex_test3(struct file *file, void *arg)
{
mutex_priv_t mp;
taskq_t *tq;
int rc = 0;
mp.mp_magic = SPLAT_MUTEX_TEST_MAGIC;
mp.mp_file = file;
mutex_init(&mp.mp_mtx, SPLAT_MUTEX_TEST_NAME, MUTEX_DEFAULT, NULL);
if ((tq = taskq_create(SPLAT_MUTEX_TEST_NAME, 1, maxclsyspri,
50, INT_MAX, TASKQ_PREPOPULATE)) == NULL) {
splat_vprint(file, SPLAT_MUTEX_TEST3_NAME, "Taskq '%s' "
"create failed\n", SPLAT_MUTEX_TEST3_NAME);
return -EINVAL;
}
mutex_enter(&mp.mp_mtx);
/* Mutex should be owned by current */
if (!mutex_owned(&mp.mp_mtx)) {
splat_vprint(file, SPLAT_MUTEX_TEST3_NAME, "Unowned mutex "
"should be owned by pid %d\n", current->pid);
rc = -EINVAL;
goto out_exit;
}
if (taskq_dispatch(tq, splat_mutex_owned, &mp, TQ_SLEEP) == 0) {
splat_vprint(file, SPLAT_MUTEX_TEST3_NAME, "Failed to "
"dispatch function '%s' to taskq\n",
sym2str(splat_mutex_owned));
rc = -EINVAL;
goto out_exit;
}
taskq_wait(tq);
/* Mutex should not be owned which checked from a different thread */
if (mp.mp_rc || mp.mp_rc2) {
splat_vprint(file, SPLAT_MUTEX_TEST3_NAME, "Mutex owned by "
"pid %d not by taskq\n", current->pid);
rc = -EINVAL;
goto out_exit;
}
mutex_exit(&mp.mp_mtx);
/* Mutex should not be owned by current */
if (mutex_owned(&mp.mp_mtx)) {
splat_vprint(file, SPLAT_MUTEX_TEST3_NAME, "Mutex owned by "
"pid %d it should be unowned\b", current->pid);
rc = -EINVAL;
goto out;
}
if (taskq_dispatch(tq, splat_mutex_owned, &mp, TQ_SLEEP) == 0) {
splat_vprint(file, SPLAT_MUTEX_TEST3_NAME, "Failed to "
"dispatch function '%s' to taskq\n",
sym2str(splat_mutex_owned));
rc = -EINVAL;
goto out;
}
taskq_wait(tq);
/* Mutex should be owned by no one */
if (mp.mp_rc || mp.mp_rc2) {
splat_vprint(file, SPLAT_MUTEX_TEST3_NAME, "Mutex owned by "
"no one, %d/%d disagrees\n", mp.mp_rc, mp.mp_rc2);
rc = -EINVAL;
goto out;
}
splat_vprint(file, SPLAT_MUTEX_TEST3_NAME, "%s",
"Correct mutex_owned() behavior\n");
goto out;
out_exit:
mutex_exit(&mp.mp_mtx);
out:
mutex_destroy(&mp.mp_mtx);
taskq_destroy(tq);
return rc;
}
static int
splat_mutex_test4(struct file *file, void *arg)
{
kmutex_t mtx;
kthread_t *owner;
int rc = 0;
mutex_init(&mtx, SPLAT_MUTEX_TEST_NAME, MUTEX_DEFAULT, NULL);
/*
* Verify mutex owner is cleared after being dropped. Depending
* on how you build your kernel this behavior changes, ensure the
* SPL mutex implementation is properly detecting this.
*/
mutex_enter(&mtx);
msleep(100);
mutex_exit(&mtx);
if (MUTEX_HELD(&mtx)) {
splat_vprint(file, SPLAT_MUTEX_TEST4_NAME, "Mutex should "
"not be held, bit is by %p\n", mutex_owner(&mtx));
rc = -EINVAL;
goto out;
}
mutex_enter(&mtx);
/* Mutex should be owned by current */
owner = mutex_owner(&mtx);
if (current != owner) {
splat_vprint(file, SPLAT_MUTEX_TEST4_NAME, "Mutex should "
"be owned by pid %d but is owned by pid %d\n",
current->pid, owner ? owner->pid : -1);
rc = -EINVAL;
goto out;
}
mutex_exit(&mtx);
/* Mutex should not be owned by any task */
owner = mutex_owner(&mtx);
if (owner) {
splat_vprint(file, SPLAT_MUTEX_TEST4_NAME, "Mutex should not "
"be owned but is owned by pid %d\n", owner->pid);
rc = -EINVAL;
goto out;
}
splat_vprint(file, SPLAT_MUTEX_TEST3_NAME, "%s",
"Correct mutex_owner() behavior\n");
out:
mutex_destroy(&mtx);
return rc;
}
splat_subsystem_t *
splat_mutex_init(void)
{
splat_subsystem_t *sub;
sub = kmalloc(sizeof(*sub), GFP_KERNEL);
if (sub == NULL)
return NULL;
memset(sub, 0, sizeof(*sub));
strncpy(sub->desc.name, SPLAT_MUTEX_NAME, SPLAT_NAME_SIZE);
strncpy(sub->desc.desc, SPLAT_MUTEX_DESC, SPLAT_DESC_SIZE);
INIT_LIST_HEAD(&sub->subsystem_list);
INIT_LIST_HEAD(&sub->test_list);
spin_lock_init(&sub->test_lock);
sub->desc.id = SPLAT_SUBSYSTEM_MUTEX;
SPLAT_TEST_INIT(sub, SPLAT_MUTEX_TEST1_NAME, SPLAT_MUTEX_TEST1_DESC,
SPLAT_MUTEX_TEST1_ID, splat_mutex_test1);
SPLAT_TEST_INIT(sub, SPLAT_MUTEX_TEST2_NAME, SPLAT_MUTEX_TEST2_DESC,
SPLAT_MUTEX_TEST2_ID, splat_mutex_test2);
SPLAT_TEST_INIT(sub, SPLAT_MUTEX_TEST3_NAME, SPLAT_MUTEX_TEST3_DESC,
SPLAT_MUTEX_TEST3_ID, splat_mutex_test3);
SPLAT_TEST_INIT(sub, SPLAT_MUTEX_TEST4_NAME, SPLAT_MUTEX_TEST4_DESC,
SPLAT_MUTEX_TEST4_ID, splat_mutex_test4);
return sub;
}
void
splat_mutex_fini(splat_subsystem_t *sub)
{
ASSERT(sub);
SPLAT_TEST_FINI(sub, SPLAT_MUTEX_TEST4_ID);
SPLAT_TEST_FINI(sub, SPLAT_MUTEX_TEST3_ID);
SPLAT_TEST_FINI(sub, SPLAT_MUTEX_TEST2_ID);
SPLAT_TEST_FINI(sub, SPLAT_MUTEX_TEST1_ID);
kfree(sub);
}
int
splat_mutex_id(void) {
return SPLAT_SUBSYSTEM_MUTEX;
}
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