use_mm/unuse_mm correctness

[Suparna Bhattacharya <suparna@in.ibm.com>]

Can anyone spot a problem in the following routines ?

These are used by AIO workqueue routines to take on the 
caller's address space when executing certain operations,
and then to switch back to the workqueue thread's original 
mm context. 

We are seeing some strange bugs in -mm lately, and this
code is one of the suspects. Can't yet see what could be
wrong ...

/*
 * use_mm
 * 	Makes the calling kernel thread take on the specified 
 * 	mm context. 
 * 	Called by the retry thread execute retries within the 
 * 	iocb issuer's mm context, so that copy_from/to_user
 * 	operations work seamlessly for aio.
 * 	(Note: this routine is intended to be called only 
 * 	from a kernel thread context)
 */
static void use_mm(struct mm_struct *mm)
{
	struct mm_struct *active_mm = current->active_mm;
	atomic_inc(&mm->mm_count);
	current->mm = mm;

	current->active_mm = mm;
	activate_mm(active_mm, mm);

	mmdrop(active_mm);
}

/*
 * unuse_mm
 * 	Reverses the effect of use_mm, i.e. releases the
 * 	specified mm context which was earlier taken on
 * 	by the calling kernel thread 
 * 	(Note: this routine is intended to be called only 
 * 	from a kernel thread context)
 */
void unuse_mm(struct mm_struct *mm)
{
	current->mm = NULL;
	/* active_mm is still 'mm' */
	enter_lazy_tlb(mm, current, smp_processor_id());
}

Regards
Suparna

-- 
Suparna Bhattacharya (suparna@in.ibm.com)
Linux Technology Center
IBM Software Labs, India

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