[PATCH] xacct_add_tsk: fix pure theoretical ->mm use-after-free

Paranoid fix. The task can free its ->mm after the 'if (p->mm)' check.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Jay Lan <jlan@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
 void xacct_add_tsk(struct taskstats *stats, struct task_struct *p)
 {
	struct mm_struct *mm;

 	/* convert pages-jiffies to Mbyte-usec */
 	stats->coremem = jiffies_to_usecs(p->acct_rss_mem1) * PAGE_SIZE / MB;
 	stats->virtmem = jiffies_to_usecs(p->acct_vm_mem1) * PAGE_SIZE / MB;
	mm = get_task_mm(p);
	if (mm) {
 		/* adjust to KB unit */
		stats->hiwater_rss   = mm->hiwater_rss * PAGE_SIZE / KB;
		stats->hiwater_vm    = mm->hiwater_vm * PAGE_SIZE / KB;
		mmput(mm);
 	}
 	stats->read_char	= p->rchar;
 	stats->write_char	= p->wchar;
	stats->read_syscalls	= p->syscr;
	stats->write_syscalls	= p->syscw;
}

 void xacct_add_tsk(struct taskstats *stats, struct task_struct *p)
 {
 	/* convert pages-jiffies to Mbyte-usec */
 	stats->coremem = jiffies_to_usecs(p->acct_rss_mem1) * PAGE_SIZE / MB;
 	stats->virtmem = jiffies_to_usecs(p->acct_vm_mem1) * PAGE_SIZE / MB;
	if (p->mm) {
 		/* adjust to KB unit */
		stats->hiwater_rss   = p->mm->hiwater_rss * PAGE_SIZE / KB;
		stats->hiwater_vm    = p->mm->hiwater_vm * PAGE_SIZE / KB;
 	}
 	stats->read_char	= p->rchar;
 	stats->write_char	= p->wchar;
	stats->read_syscalls	= p->syscr;
	stats->write_syscalls	= p->syscw;
}
