diff mbox

ARM64: kernel oops in 4.4-rc4+

Message ID 20151208120625.GA26759@e104818-lin.cambridge.arm.com
State New
Headers show

Commit Message

Catalin Marinas Dec. 8, 2015, 12:06 p.m. UTC 
On Tue, Dec 08, 2015 at 10:51:52AM +0000, Will Deacon wrote:
> On Tue, Dec 08, 2015 at 10:30:13AM +0000, Will Deacon wrote:

> > On Tue, Dec 08, 2015 at 02:30:33PM +0800, Ming Lei wrote:

> > > The attached kernel oops can be triggered immediately after

> > > running the following command on APM Mustang:

> > > 

> > >         $stress-ng --all 8 -t 10m

> > > 

> > > [1] kernel oops log

> > > stress-ng: info:  [5220] 5 failures reached, aborting stress process

> > > [  265.782659] kernel BUG at ./arch/arm64/include/asm/pgtable.h:282!

> > 

> > Yikes, this means we're replacing a writable pte with a clean pte, so

> > there's a potential race w/ hardware DBM.

> > 

> > Could you dump pte and *ptep please?

> 

> I tried running this on my Juno and pretty quickly saw the OOM killer

> coming in. Perhaps, in your case, pte is a swap entry and its confusing

> the checks (so pte_dirty/pte_young are looking at random bits of the

> file offset)?


It could indeed be that the new pte is swap or file and the check misses
that. The easiest is to move the check inside the if (pte_valid_user(pte))
block:

--------------8<------------------------
--------------8<------------------------

-- 
Catalin

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diff mbox

Patch

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 7e074f93f383..12d89ee5ab7f 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -269,17 +269,17 @@  static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
 			pte_val(pte) &= ~PTE_RDONLY;
 		else
 			pte_val(pte) |= PTE_RDONLY;
-	}
 
-	/*
-	 * If the existing pte is valid, check for potential race with
-	 * hardware updates of the pte (ptep_set_access_flags safely changes
-	 * valid ptes without going through an invalid entry).
-	 */
-	if (IS_ENABLED(CONFIG_DEBUG_VM) && IS_ENABLED(CONFIG_ARM64_HW_AFDBM) &&
-	    pte_valid(*ptep)) {
-		BUG_ON(!pte_young(pte));
-		BUG_ON(pte_write(*ptep) && !pte_dirty(pte));
+		/*
+		 * If the existing pte is valid, check for potential race with
+		 * hardware updates of the pte (ptep_set_access_flags safely
+		 * changes valid ptes without going through an invalid entry).
+		 */
+		if (IS_ENABLED(CONFIG_DEBUG_VM) && IS_ENABLED(CONFIG_ARM64_HW_AFDBM) &&
+		    pte_valid(*ptep)) {
+			BUG_ON(!pte_young(pte));
+			BUG_ON(pte_write(*ptep) && !pte_dirty(pte));
+		}
 	}
 
 	set_pte(ptep, pte);