Hi Andrew, On Thu, Jan 31, 2013 at 01:50:42PM -0800, Andrew Morton wrote: > On Thu, 24 Jan 2013 18:24:14 +0800 > Shaohua Li <shli@xxxxxxxxxx> wrote: > > > Subject: mm: add memory barrier to prevent SwapCache bit and page private out of order > > > > page_mapping() checks SwapCache bit first and then read page private. Adding > > memory barrier so page private has correct value before SwapCache bit set. > > > > In some cases, page_mapping() isn't called with page locked. Without doing > > this, we might get a wrong swap address space with SwapCache bit set. Though I > > didn't found a problem with this so far (such code typically only checks if the > > page has mapping or the mapping can be dirty or migrated), this is too subtle > > and error-prone, so we want to avoid it. > > > > ... > > > > --- linux.orig/mm/swap_state.c 2013-01-22 10:12:33.514490665 +0800 > > +++ linux/mm/swap_state.c 2013-01-24 18:08:05.149390977 +0800 > > @@ -89,6 +89,7 @@ static int __add_to_swap_cache(struct pa > > > > page_cache_get(page); > > set_page_private(page, entry.val); > > + smp_wmb(); > > SetPageSwapCache(page); > > SetPageSwapCache() uses set_bit() and arch/x86/include/asm/bitops.h > says "This function is atomic and may not be reordered". And says below. * Note: there are no guarantees that this function will not be reordered * on non x86 architectures, so if you are writing portable code, * make sure not to rely on its reordering guarantees. -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>