Re: [PATCH] arch: metag: kernel: dma.c: check 'pud' whether is NULL in dma_alloc_init()

[James Hogan <james.hogan-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>]

On 14/11/13 09:35, Chen Gang wrote:
> On 11/14/2013 05:18 PM, James Hogan wrote:
>> On Thursday 14 November 2013 16:11:21 Chen Gang wrote:
>>> Like another p?d_alloc(), pud_alloc() also may fail, so need check it.
>>>
>>> Signed-off-by: Chen Gang <gang.chen-bOixZGp5f+dBDgjK7y7TUQ@public.gmane.org>
>>
>> NAK.
>>
>> pud_alloc folds to pud_offset on Meta so it cannot fail.
>>
> 
> If so, can pmd_alloc() be fail?

No. pmd_alloc folds to pmd_offset so it also cannot fail, and the
existing !pmd check is dead code. The following would be better.

Cheers
James

From 85a386a9c7df666b1f438435be8a89581bc7e8b3 Mon Sep 17 00:00:00 2001
From: James Hogan <james.hogan-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>
Date: Thu, 14 Nov 2013 10:14:37 +0000
Subject: [PATCH 1/1] metag: dma: remove dead code in dma_alloc_init()

Meta has 2 levels of page table so the pmd folds into the pud which
folds into the pgd. Therefore the !pmd check in dma_alloc_init() is dead
code since it essentially checks whether:
  (init_mm->pgd + 0x770) == 0

Remove the check.

Reported-by: Chen Gang <gang.chen-bOixZGp5f+dBDgjK7y7TUQ@public.gmane.org>
Signed-off-by: James Hogan <james.hogan-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org>
---
 arch/metag/kernel/dma.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/arch/metag/kernel/dma.c b/arch/metag/kernel/dma.c
index 8c00dedadc54..78205dbc2b86 100644
--- a/arch/metag/kernel/dma.c
+++ b/arch/metag/kernel/dma.c
@@ -401,11 +401,6 @@ static int __init dma_alloc_init(void)
 		pgd = pgd_offset(&init_mm, CONSISTENT_START);
 		pud = pud_alloc(&init_mm, pgd, CONSISTENT_START);
 		pmd = pmd_alloc(&init_mm, pud, CONSISTENT_START);
-		if (!pmd) {
-			pr_err("%s: no pmd tables\n", __func__);
-			ret = -ENOMEM;
-			break;
-		}
 		WARN_ON(!pmd_none(*pmd));
 
 		pte = pte_alloc_kernel(pmd, CONSISTENT_START);
-- 
1.8.1.2

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