• Shailabh Nagar's avatar
    [PATCH] task delay accounting fixes · 35df17c5
    Shailabh Nagar authored
    Cleanup allocation and freeing of tsk->delays used by delay accounting.
    This solves two problems reported for delay accounting:
    
    1. oops in __delayacct_blkio_ticks
    http://www.uwsg.indiana.edu/hypermail/linux/kernel/0608.2/1844.html
    
    Currently tsk->delays is getting freed too early in task exit which can
    cause a NULL tsk->delays to get accessed via reading of /proc/<tgid>/stats.
     The patch fixes this problem by freeing tsk->delays closer to when
    task_struct itself is freed up.  As a result, it also eliminates the use of
    tsk->delays_lock which was only being used (inadequately) to safeguard
    access to tsk->delays while a task was exiting.
    
    2. Possible memory leak in kernel/delayacct.c
    http://www.uwsg.indiana.edu/hypermail/linux/kernel/0608.2/1389.html
    
    
    
    The patch cleans up tsk->delays allocations after a bad fork which was
    missing earlier.
    
    The patch has been tested to fix the problems listed above and stress
    tested with rapid calls to delay accounting's taskstats command interface
    (which is the other path that can access the same data, besides the /proc
    interface causing the oops above).
    Signed-off-by: default avatarShailabh Nagar <nagar@watson.ibm.com>
    Cc: Balbir Singh <balbir@in.ibm.com>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    35df17c5
delayacct.c 4.18 KB
/* delayacct.c - per-task delay accounting
 *
 * Copyright (C) Shailabh Nagar, IBM Corp. 2006
 *
 * 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 would 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.
 */

#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/sysctl.h>
#include <linux/delayacct.h>

int delayacct_on __read_mostly = 1;	/* Delay accounting turned on/off */
kmem_cache_t *delayacct_cache;

static int __init delayacct_setup_disable(char *str)
{
	delayacct_on = 0;
	return 1;
}
__setup("nodelayacct", delayacct_setup_disable);

void delayacct_init(void)
{
	delayacct_cache = kmem_cache_create("delayacct_cache",
					sizeof(struct task_delay_info),
					0,
					SLAB_PANIC,
					NULL, NULL);
	delayacct_tsk_init(&init_task);
}

void __delayacct_tsk_init(struct task_struct *tsk)
{
	tsk->delays = kmem_cache_zalloc(delayacct_cache, SLAB_KERNEL);
	if (tsk->delays)
		spin_lock_init(&tsk->delays->lock);
}

/*
 * Start accounting for a delay statistic using
 * its starting timestamp (@start)
 */

static inline void delayacct_start(struct timespec *start)
{
	do_posix_clock_monotonic_gettime(start);
}

/*
 * Finish delay accounting for a statistic using
 * its timestamps (@start, @end), accumalator (@total) and @count
 */

static void delayacct_end(struct timespec *start, struct timespec *end,
				u64 *total, u32 *count)
{
	struct timespec ts;
	s64 ns;

	do_posix_clock_monotonic_gettime(end);
	ts = timespec_sub(*end, *start);
	ns = timespec_to_ns(&ts);
	if (ns < 0)
		return;

	spin_lock(&current->delays->lock);
	*total += ns;
	(*count)++;
	spin_unlock(&current->delays->lock);
}

void __delayacct_blkio_start(void)
{
	delayacct_start(&current->delays->blkio_start);
}

void __delayacct_blkio_end(void)
{
	if (current->delays->flags & DELAYACCT_PF_SWAPIN)
		/* Swapin block I/O */
		delayacct_end(&current->delays->blkio_start,
			&current->delays->blkio_end,
			&current->delays->swapin_delay,
			&current->delays->swapin_count);
	else	/* Other block I/O */
		delayacct_end(&current->delays->blkio_start,
			&current->delays->blkio_end,
			&current->delays->blkio_delay,
			&current->delays->blkio_count);
}

int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
{
	s64 tmp;
	struct timespec ts;
	unsigned long t1,t2,t3;

	/* Though tsk->delays accessed later, early exit avoids
	 * unnecessary returning of other data
	 */
	if (!tsk->delays)
		goto done;

	tmp = (s64)d->cpu_run_real_total;
	cputime_to_timespec(tsk->utime + tsk->stime, &ts);
	tmp += timespec_to_ns(&ts);
	d->cpu_run_real_total = (tmp < (s64)d->cpu_run_real_total) ? 0 : tmp;

	/*
	 * No locking available for sched_info (and too expensive to add one)
	 * Mitigate by taking snapshot of values
	 */
	t1 = tsk->sched_info.pcnt;
	t2 = tsk->sched_info.run_delay;
	t3 = tsk->sched_info.cpu_time;

	d->cpu_count += t1;

	jiffies_to_timespec(t2, &ts);
	tmp = (s64)d->cpu_delay_total + timespec_to_ns(&ts);
	d->cpu_delay_total = (tmp < (s64)d->cpu_delay_total) ? 0 : tmp;

	tmp = (s64)d->cpu_run_virtual_total + (s64)jiffies_to_usecs(t3) * 1000;
	d->cpu_run_virtual_total =
		(tmp < (s64)d->cpu_run_virtual_total) ?	0 : tmp;

	/* zero XXX_total, non-zero XXX_count implies XXX stat overflowed */

	spin_lock(&tsk->delays->lock);
	tmp = d->blkio_delay_total + tsk->delays->blkio_delay;
	d->blkio_delay_total = (tmp < d->blkio_delay_total) ? 0 : tmp;
	tmp = d->swapin_delay_total + tsk->delays->swapin_delay;
	d->swapin_delay_total = (tmp < d->swapin_delay_total) ? 0 : tmp;
	d->blkio_count += tsk->delays->blkio_count;
	d->swapin_count += tsk->delays->swapin_count;
	spin_unlock(&tsk->delays->lock);

done:
	return 0;
}

__u64 __delayacct_blkio_ticks(struct task_struct *tsk)
{
	__u64 ret;

	spin_lock(&tsk->delays->lock);
	ret = nsec_to_clock_t(tsk->delays->blkio_delay +
				tsk->delays->swapin_delay);
	spin_unlock(&tsk->delays->lock);
	return ret;
}