Commit 35df17c5 authored by Shailabh Nagar's avatar Shailabh Nagar Committed by Linus Torvalds
Browse files

[PATCH] task delay accounting fixes 

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>
parent 30f3174d

include/linux/delayacct.h

+7 −3
Original line number Diff line number Diff line
@@ -59,10 +59,14 @@ static inline void delayacct_tsk_init(struct task_struct *tsk) 
		__delayacct_tsk_init(tsk);

}



static inline void delayacct_tsk_exit(struct task_struct *tsk)

/* Free tsk->delays. Called from bad fork and __put_task_struct

 * where there's no risk of tsk->delays being accessed elsewhere

 */

static inline void delayacct_tsk_free(struct task_struct *tsk)

{

	if (tsk->delays)

		__delayacct_tsk_exit(tsk);

		kmem_cache_free(delayacct_cache, tsk->delays);

	tsk->delays = NULL;

}



static inline void delayacct_blkio_start(void)
@@ -101,7 +105,7 @@ static inline void delayacct_init(void) 
{}

static inline void delayacct_tsk_init(struct task_struct *tsk)

{}

static inline void delayacct_tsk_exit(struct task_struct *tsk)

static inline void delayacct_tsk_free(struct task_struct *tsk)

{}

static inline void delayacct_blkio_start(void)

{}

include/linux/sched.h

+0 −1
Original line number Diff line number Diff line
@@ -994,7 +994,6 @@ struct task_struct { 
	 */

	struct pipe_inode_info *splice_pipe;

#ifdef	CONFIG_TASK_DELAY_ACCT

	spinlock_t delays_lock;

	struct task_delay_info *delays;

#endif

};

kernel/delayacct.c

+0 −16
Original line number Diff line number Diff line
@@ -41,24 +41,11 @@ void delayacct_init(void) 


void __delayacct_tsk_init(struct task_struct *tsk)

{

	spin_lock_init(&tsk->delays_lock);

	/* No need to acquire tsk->delays_lock for allocation here unless

	   __delayacct_tsk_init called after tsk is attached to tasklist

	*/

	tsk->delays = kmem_cache_zalloc(delayacct_cache, SLAB_KERNEL);

	if (tsk->delays)

		spin_lock_init(&tsk->delays->lock);

}



void __delayacct_tsk_exit(struct task_struct *tsk)

{

	struct task_delay_info *delays = tsk->delays;

	spin_lock(&tsk->delays_lock);

	tsk->delays = NULL;

	spin_unlock(&tsk->delays_lock);

	kmem_cache_free(delayacct_cache, delays);

}



/*

 * Start accounting for a delay statistic using

 * its starting timestamp (@start)
@@ -118,8 +105,6 @@ int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk) 
	struct timespec ts;

	unsigned long t1,t2,t3;



	spin_lock(&tsk->delays_lock);



	/* Though tsk->delays accessed later, early exit avoids

	 * unnecessary returning of other data

	 */
@@ -161,7 +146,6 @@ int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk) 
	spin_unlock(&tsk->delays->lock);



done:

	spin_unlock(&tsk->delays_lock);

	return 0;

}

kernel/exit.c

+0 −1
Original line number Diff line number Diff line
@@ -908,7 +908,6 @@ fastcall NORET_TYPE void do_exit(long code) 
		audit_free(tsk);

	taskstats_exit_send(tsk, tidstats, group_dead, mycpu);

	taskstats_exit_free(tidstats);

	delayacct_tsk_exit(tsk);



	exit_mm(tsk);

kernel/fork.c

+4 −2
Original line number Diff line number Diff line
@@ -117,6 +117,7 @@ void __put_task_struct(struct task_struct *tsk) 
	security_task_free(tsk);

	free_uid(tsk->user);

	put_group_info(tsk->group_info);

	delayacct_tsk_free(tsk);



	if (!profile_handoff_task(tsk))

		free_task(tsk);
@@ -1011,7 +1012,7 @@ static struct task_struct *copy_process(unsigned long clone_flags, 
	retval = -EFAULT;

	if (clone_flags & CLONE_PARENT_SETTID)

		if (put_user(p->pid, parent_tidptr))

			goto bad_fork_cleanup;

			goto bad_fork_cleanup_delays_binfmt;



	INIT_LIST_HEAD(&p->children);

	INIT_LIST_HEAD(&p->sibling);
@@ -1277,7 +1278,8 @@ bad_fork_cleanup_policy: 
bad_fork_cleanup_cpuset:

#endif

	cpuset_exit(p);

bad_fork_cleanup:

bad_fork_cleanup_delays_binfmt:

	delayacct_tsk_free(p);

	if (p->binfmt)

		module_put(p->binfmt->module);

bad_fork_cleanup_put_domain:

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