[IA64] Fix race in the accessed/dirty bit handlers (d8117ce5) · Commits · 戴 / test

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 <clameter@sgi.com> Signed-off-by:

Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/ivt.S

+9 −6

Original line number	Diff line number	Diff line
		@@ -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
		/*

Admin message