On Friday 23 June 2006 13:56, Vernon Mauery wrote:
> On Sunday 18 June 2006 00:06, Ingo Molnar wrote:
> > i have released the 2.6.17-rt1 tree, which can be downloaded from the
> > usual place:
>
> I was given a test case to run that seemed to cause the machine to run the
> OOM-killer after a bunch of iterations. The test was run like:
>
> $ for ((i=0;i<50000;i++)); do ./test; done
>
> and somewhere in there, the LowFree would drop very low and the test and
> the bash shell running it would get killed. And then since that didn't
> free up much memory, the machine would become very unresponsive and would
> have to be rebooted.
I found the problem -- it was in the PI futex code -- lock_queue was getting
called essentially twice in a row and was continually incrementing the
mm_count ref count, thus causing the memory leak. Not completely
understanding all the intricacies of the PI futex code, I just suggested to
no make the second call to lock_queue (not realizing __queue_me unlocks the
queue). Dinakar Guniguntala provided a proper fix for the problem that
simply grabs the spinlock for the hash bucket queue rather than calling
lock_queue. His fix is below and applies to 2.6.17-rt4.
Attached is a test case I wrote to reproduce the problem.
--Vernon
The second time we do a queue_lock in futex_lock_pi, we really only need to
take the hash bucket lock.
Signed-off-by: Dinakar Guniguntala <[email protected]>
Signed-off-by: Vernon Mauery <[email protected]>
Acked-by: Paul E. McKenney <[email protected]>
Index: linux-2.6.17-rt4/kernel/futex.c
===================================================================
--- a/kernel/futex.c 2006-06-30 04:39:29.000000000 -0700
+++ b/kernel/futex.c 2006-06-30 04:46:52.000000000 -0700
@@ -1269,7 +1269,7 @@
}
down_read(&curr->mm->mmap_sem);
- hb = queue_lock(&q, -1, NULL);
+ spin_lock(q.lock_ptr);
/*
* Got the lock. We might not be the anticipated owner if we
/* Filename: mm_leak.c
* Author: Vernon Mauery <[email protected]>
* Description: force a kernel memory leak using pi mutexes
* Compilation: gcc mm_leak.c -lm -L/usr/lib/nptl -lpthread -lrt -D_GNU_SOURCE -I/usr/include/nptl -o mm_leak
*
* This program 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.
*
* This program 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 this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright (C) IBM Corporation, 2006
*
* 2006-May-3: Initial version by Darren Hart <[email protected]>
* 2006-May-4: Timing fixes reported by Vernon Mauery <[email protected]>
* 2006-May-4: Made the med prio threads RT by Darren Hart <[email protected]>
* 2006-May-5: Modified to use flagging by Vernon Mauery <[email protected]>
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <sched.h>
#define HIGH_PRIO 15
#define ITERATIONS 100
static int count = 0;
static pthread_mutex_t pi_mutex;
struct thread {
pthread_t pthread;
pthread_attr_t attr;
};
int create_fifo_thread(struct thread *thread, void*(*func)(void*), void *arg, int prio)
{
struct sched_param param;
param.sched_priority = sched_get_priority_min(SCHED_FIFO) + prio;
pthread_attr_init(&thread->attr);
pthread_attr_setinheritsched(&thread->attr, PTHREAD_EXPLICIT_SCHED);
pthread_attr_setschedparam(&thread->attr, ¶m);
pthread_attr_setschedpolicy(&thread->attr, SCHED_FIFO);
if (pthread_create(&thread->pthread, &thread->attr, func, (void*)arg)) {
perror("pthread_create failed");
return 1;
}
pthread_attr_destroy(&thread->attr);
return 0;
}
void init_pi_mutex(pthread_mutex_t *m, int use_pi)
{
pthread_mutexattr_t attr;
int ret;
int protocol;
if (pthread_mutexattr_init(&attr) != 0) {
printf("Failed to init mutexattr\n");
}
if (use_pi) {
if (pthread_mutexattr_setprotocol(&attr, PTHREAD_PRIO_INHERIT) != 0) {
printf("Can't set protocol prio inherit\n");
}
}
if (pthread_mutexattr_getprotocol(&attr, &protocol) != 0) {
printf("Can't get mutexattr protocol\n");
}
if ((ret = pthread_mutex_init(m, &attr)) != 0) {
printf("Failed to init mutex: %d\n", ret);
}
/* FIXME: does any of this need to be destroyed ? */
}
#define THREADS 2
void *thread_one(void *arg)
{
int iterations = (int)arg;
while (count < iterations) {
while (1) {
pthread_mutex_lock(&pi_mutex);
if (count % THREADS == 1)
break;
pthread_mutex_unlock(&pi_mutex);
usleep(10);
}
printf("1"); fflush(NULL);
count++;
pthread_mutex_unlock(&pi_mutex);
}
return NULL;
}
void *thread_zero(void *arg) {
int iterations = (int)arg;
while (count < iterations) {
while (1) {
pthread_mutex_lock(&pi_mutex);
if (count % THREADS == 0)
break;
pthread_mutex_unlock(&pi_mutex);
usleep(1);
}
printf("0"); fflush(NULL);
count++;
pthread_mutex_unlock(&pi_mutex);
}
return NULL;
}
int main(int argc, char *argv[])
{
struct thread one;
int iterations = ITERATIONS;
int pi = 1, c;
while ((c=getopt(argc, argv, "i:ph")) >= 0) {
if (c == 'i') {
iterations = atoi(optarg);
} else if (c == 'p') {
pi = 0;
} else {
printf("usage: %s [-i iterations] [-p] [-h]\n", argv[0]);
printf("\t -i iterations\n");
printf("\t -p -- do not use pi mutexes\n");
printf("\t -h -- print this message\n");
exit(0);
}
}
/* creating the mutex as a PI mutex causes a kernel memory leak */
init_pi_mutex(&pi_mutex, pi);
create_fifo_thread(&one, thread_one, (void*)iterations, HIGH_PRIO);
thread_zero((void*)iterations);
pthread_join(one.pthread, NULL);
printf("\n");
return 0;
}
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