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Message-ID: <44EB5794.9020205@watson.ibm.com>
Date: Tue, 22 Aug 2006 15:14:28 -0400
From: Shailabh Nagar <nagar@...son.ibm.com>
To: Catalin Marinas <catalin.marinas@...il.com>
CC: Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
linux-kernel <linux-kernel@...r.kernel.org>,
Balbir Singh <balbir@...ibm.com>
Subject: Re: Possible memory leak in kernel/delayacct.c
Catalin Marinas wrote:
> Hi Shailabh,
>
> Michal was running some kmemleak tests and there are about 20 orphan
> pointers reported in delayacct.c. The allocation backtrace is:
>
> orphan pointer 0xf548fde0 (size 76):
> c0174674: <kmem_cache_zalloc>
> c01591ee: <__delayacct_tsk_init>
> c0127e06: <copy_process>
> c0128cd2: <do_fork>
> c0104d39: <sys_clone>
>
> I'm not sure whether the leak occurs but there might be a path where
> task_struct is freed and the task->delays pointer is lost. Could you
> please have a look at this? Thanks.
>
One possibility for the leak is a missing free for tsk->delays on a
failed fork. Were the kmemleak tests causing fork failures to happen ?
What was being run in userspace ? Since the tsk->delays get allocated
from a slab, it should be easy enough to detect.
Could you try the patch below ? Its also being used for an oops reported
for delay accounting.
Thanks,
Shailabh
Cleanup allocation and freeing of tsk->delays used by delay accounting.
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.
The patch also cleans up tsk->delays allocations after a bad fork which
was missing earlier and might lead to leaks.
Signed-Off-By: Shailabh Nagar <nagar@...son.ibm.com>
include/linux/delayacct.h | 10 +++++++---
include/linux/sched.h | 1 -
kernel/delayacct.c | 16 ----------------
kernel/exit.c | 1 -
kernel/fork.c | 6 ++++--
5 files changed, 11 insertions(+), 23 deletions(-)
Index: linux-2.6.18-rc4/kernel/fork.c
===================================================================
--- linux-2.6.18-rc4.orig/kernel/fork.c 2006-08-22 14:42:08.000000000 -0400
+++ linux-2.6.18-rc4/kernel/fork.c 2006-08-22 14:52:52.000000000 -0400
@@ -117,6 +117,7 @@ void __put_task_struct(struct task_struc
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(
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:
Index: linux-2.6.18-rc4/include/linux/delayacct.h
===================================================================
--- linux-2.6.18-rc4.orig/include/linux/delayacct.h 2006-08-22 14:42:03.000000000 -0400
+++ linux-2.6.18-rc4/include/linux/delayacct.h 2006-08-22 14:52:52.000000000 -0400
@@ -59,10 +59,14 @@ static inline void delayacct_tsk_init(st
__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)
{}
Index: linux-2.6.18-rc4/include/linux/sched.h
===================================================================
--- linux-2.6.18-rc4.orig/include/linux/sched.h 2006-08-22 14:42:03.000000000 -0400
+++ linux-2.6.18-rc4/include/linux/sched.h 2006-08-22 14:52:52.000000000 -0400
@@ -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
};
Index: linux-2.6.18-rc4/kernel/exit.c
===================================================================
--- linux-2.6.18-rc4.orig/kernel/exit.c 2006-08-22 14:42:03.000000000 -0400
+++ linux-2.6.18-rc4/kernel/exit.c 2006-08-22 14:52:52.000000000 -0400
@@ -908,7 +908,6 @@ fastcall NORET_TYPE void do_exit(long co
audit_free(tsk);
taskstats_exit_send(tsk, tidstats, group_dead, mycpu);
taskstats_exit_free(tidstats);
- delayacct_tsk_exit(tsk);
exit_mm(tsk);
Index: linux-2.6.18-rc4/kernel/delayacct.c
===================================================================
--- linux-2.6.18-rc4.orig/kernel/delayacct.c 2006-08-22 14:42:03.000000000 -0400
+++ linux-2.6.18-rc4/kernel/delayacct.c 2006-08-22 14:52:52.000000000 -0400
@@ -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
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
spin_unlock(&tsk->delays->lock);
done:
- spin_unlock(&tsk->delays_lock);
return 0;
}
-
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