linux-kernel - Why should check "current" consistency?

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Date:	Mon, 8 Mar 2010 10:21:06 +0800
From:	real yr <realyr@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Why should check "current" consistency?

The source code is listed as follows:
This code is inserted into do_fork() function
============================================
struct asmp_cpu_info *info;
......
restart:
if ((info = current->asmp->cpu)) {
dprintk("forking tsk=%p current=%p #tasks=%d\n", p, current,
info->num_tasks);
spin_lock_irqsave(&info->lock, flags);
                /* MY PROBLEM */
if (info != current->asmp->cpu) {
spin_unlock_irqrestore(&info->lock, flags);
goto restart;
}
WARN_ON(info->shielded != 1);
WARN_ON(info->num_tasks == 0);
p->asmp->cpu = info;
list_add_tail(&p->asmp->list, &info->tasks);
++info->num_tasks;
spin_unlock_irqrestore(&info->lock, flags);
}
=========================================
Please see the code with comments "/* MY PROBLEM */", since info is a
local variable,
even if this code was preempted or interrupted, when the attached
process resumes its
state, it will continues from where it was interrupted and the
"current" macro shold be the same.
So, Why should check "if (info != current->asmp->cpu) {" ?

Thanks in advance!
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