linux-kernel - Re: sparc64 WARNING: at mm/mmap.c:2757 exit

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Date:	Wed, 30 Jul 2014 15:07:22 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mroos@...ux.ee
Cc:	aaro.koskinen@....fi, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org, hughd@...gle.com,
	cat.schulze@...ce-dsl.net
Subject: Re: sparc64 WARNING: at mm/mmap.c:2757 exit_mmap+0x13c/0x160()

From: Meelis Roos <mroos@...ux.ee>
Date: Thu, 31 Jul 2014 01:02:53 +0300 (EEST)

>> Here is something I'd like you guys to test.
> 
> Very interesting.
> 
> [...]
>> Could you guys please try this patch below?  Thanks.
> 
>   CC      arch/sparc/mm/init_64.o
> arch/sparc/mm/init_64.c: In function 'update_mmu_cache_pmd':
> arch/sparc/mm/init_64.c:2625:6: error: 'pte' may be used uninitialized in this function [-Werror=uninitialized]
> 
> gcc 4.6.4.

I'm very disappointed that gcc-4.6.3 didn't say anything to me about
this :-)

Here is a fixed patch, thanks.

diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
index 16b58ff..db5ddde 100644
--- a/arch/sparc/mm/init_64.c
+++ b/arch/sparc/mm/init_64.c
@@ -351,6 +351,10 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long address, pte_t *
 
 	mm = vma->vm_mm;
 
+	/* Don't insert a non-valid PTE into the TSB, we'll deadlock.  */
+	if (!pte_accessible(mm, pte))
+		return;
+
 	spin_lock_irqsave(&mm->context.lock, flags);
 
 #if defined(CONFIG_HUGETLB_PAGE) || defined(CONFIG_TRANSPARENT_HUGEPAGE)
@@ -2619,6 +2623,10 @@ void update_mmu_cache_pmd(struct vm_area_struct *vma, unsigned long addr,
 
 	pte = pmd_val(entry);
 
+	/* Don't insert a non-valid PMD into the TSB, we'll deadlock.  */
+	if (!(pte & _PAGE_VALID))
+		return;
+
 	/* We are fabricating 8MB pages using 4MB real hw pages.  */
 	pte |= (addr & (1UL << REAL_HPAGE_SHIFT));
 
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