From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chen Gang Subject: Re: [PATCH] arch: metag: kernel: dma.c: check 'pud' whether is NULL in dma_alloc_init() Date: Thu, 14 Nov 2013 21:35:54 +0800 Message-ID: <5284D1BA.60107@asianux.com> References: <528485A9.5050509@asianux.com> <3903789.hqVScy5mZk@radagast> <52849961.10502@asianux.com> <5284A4CF.5070809@imgtec.com> <5284B809.6010709@huawei.com> <5284B93D.1000707@imgtec.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5284B93D.1000707-1AXoQHu6uovQT0dZR+AlfA@public.gmane.org> Sender: linux-metag-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: James Hogan Cc: Xishi Qiu , Andrew Morton , linux-metag-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On 11/14/2013 07:51 PM, James Hogan wrote: > On 14/11/13 11:46, Xishi Qiu wrote: >> On 2013/11/14 18:24, James Hogan wrote: >> >>> 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 >>>>> >>>>> 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 >>> >> >> Hi James, >> >> __PAGETABLE_PUD_FOLDED and __PAGETABLE_PMD_FOLDED are defined, >> so __pud_alloc() and __pmd_alloc() always return 0, >> and pud_offset() just return (pud_t *)pgd, pmd_offset() just return (pmd_t *)pud, >> is that right? > > Yes exactly (although technically __pud_alloc() and __pmd_alloc() would > never get called due to pgd_none() and pud_none() returning 0, but it > makes little difference). > Thank all of you (originally, I did not notice about "linux/mm.h" include "asm/pgtable.h" -- which maybe be a common sense). :-) > Cheers > James > >> >>> >From 85a386a9c7df666b1f438435be8a89581bc7e8b3 Mon Sep 17 00:00:00 2001 >>> From: James Hogan >>> 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 >>> Signed-off-by: James Hogan >>> --- >>> 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); >> >> > > > -- Chen Gang -- To unsubscribe from this list: send the line "unsubscribe linux-metag" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html