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[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: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Shailabh Nagar 2006-08-31 21:27:38 -07:00 committed by Linus Torvalds
parent 30f3174d1c
commit 35df17c57c
5 changed files with 11 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
include/linux/delayacct.h
View File

@ -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)
{}

1
include/linux/sched.h
View File

@ -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
};

16
kernel/delayacct.c
View File

@ -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;
}

1
kernel/exit.c
View File

@ -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);

6
kernel/fork.c
View File

@ -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: