From d8117ce5a679ff1f48df247da30fb62c16d562c5 Mon Sep 17 00:00:00 2001 From: Christoph Lameter Date: Tue, 7 Mar 2006 19:05:32 -0800 Subject: [PATCH] [IA64] Fix race in the accessed/dirty bit handlers A pte may be zapped by the swapper, exiting process, unmapping or page migration while the accessed or dirty bit handers are about to run. In that case the accessed bit or dirty is set on an zeroed pte which leads the VM to conclude that this is a swap pte. This may lead to - Messages from the vm like swap_free: Bad swap file entry 4000000000000000 - Processes being aborted swap_dup: Bad swap file entry 4000000000000000 VM: killing process .... Page migration is particular suitable for the creation of this race since it needs to remove and restore page table entries. The fix here is to check for the present bit and simply not update the pte if the page is not present anymore. If the page is not present then the fault handler should run next which will take care of the problem by bringing the page back and then mark the page dirty or move it onto the active list. Signed-off-by: Christoph Lameter Signed-off-by: Tony Luck --- arch/ia64/kernel/ivt.S | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/arch/ia64/kernel/ivt.S b/arch/ia64/kernel/ivt.S index 9f80569a32..dcd906fe57 100644 --- a/arch/ia64/kernel/ivt.S +++ b/arch/ia64/kernel/ivt.S @@ -561,11 +561,12 @@ ENTRY(dirty_bit) ;; // avoid RAW on r18 mov ar.ccv=r18 // set compare value for cmpxchg or r25=_PAGE_D|_PAGE_A,r18 // set the dirty and accessed bits + tbit.z p7,p6 = r18,_PAGE_P_BIT // Check present bit ;; - cmpxchg8.acq r26=[r17],r25,ar.ccv +(p6) cmpxchg8.acq r26=[r17],r25,ar.ccv // Only update if page is present mov r24=PAGE_SHIFT<<2 ;; - cmp.eq p6,p7=r26,r18 +(p6) cmp.eq p6,p7=r26,r18 // Only compare if page is present ;; (p6) itc.d r25 // install updated PTE ;; @@ -626,11 +627,12 @@ ENTRY(iaccess_bit) ;; mov ar.ccv=r18 // set compare value for cmpxchg or r25=_PAGE_A,r18 // set the accessed bit + tbit.z p7,p6 = r18,_PAGE_P_BIT // Check present bit ;; - cmpxchg8.acq r26=[r17],r25,ar.ccv +(p6) cmpxchg8.acq r26=[r17],r25,ar.ccv // Only if page present mov r24=PAGE_SHIFT<<2 ;; - cmp.eq p6,p7=r26,r18 +(p6) cmp.eq p6,p7=r26,r18 // Only if page present ;; (p6) itc.i r25 // install updated PTE ;; @@ -680,11 +682,12 @@ ENTRY(daccess_bit) ;; // avoid RAW on r18 mov ar.ccv=r18 // set compare value for cmpxchg or r25=_PAGE_A,r18 // set the dirty bit + tbit.z p7,p6 = r18,_PAGE_P_BIT // Check present bit ;; - cmpxchg8.acq r26=[r17],r25,ar.ccv +(p6) cmpxchg8.acq r26=[r17],r25,ar.ccv // Only if page is present mov r24=PAGE_SHIFT<<2 ;; - cmp.eq p6,p7=r26,r18 +(p6) cmp.eq p6,p7=r26,r18 // Only if page is present ;; (p6) itc.d r25 // install updated PTE /* -- 2.39.5