On Tue, 12 Apr 2011 10:04:15 +0900 (JST) KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> wrote: > Hi > > > > zone->all_unreclaimable and zone->pages_scanned are neigher atomic > > > variables nor protected by lock. Therefore zones can become a state > > > of zone->page_scanned=0 and zone->all_unreclaimable=1. In this case, > > > current all_unreclaimable() return false even though > > > zone->all_unreclaimabe=1. > > > > > > Is this ignorable minor issue? No. Unfortunatelly, x86 has very > > > small dma zone and it become zone->all_unreclamble=1 easily. and > > > if it become all_unreclaimable=1, it never restore all_unreclaimable=0. > > > Why? if all_unreclaimable=1, vmscan only try DEF_PRIORITY reclaim and > > > a-few-lru-pages>>DEF_PRIORITY always makes 0. that mean no page scan > > > at all! > > > > > > Eventually, oom-killer never works on such systems. That said, we > > > can't use zone->pages_scanned for this purpose. This patch restore > > > all_unreclaimable() use zone->all_unreclaimable as old. and in addition, > > > to add oom_killer_disabled check to avoid reintroduce the issue of > > > commit d1908362. > > > > The above is a nice analysis of the bug and how it came to be > > introduced. But we don't actually have a bug description! What was > > the observeable problem which got fixed? > > The above says "Eventually, oom-killer never works". Is this no enough? > The above says > 1) current logic have a race > 2) x86 increase a chance of the race by dma zone > 3) if race is happen, oom killer don't work And the system hangs up, so it's a local DoS and I guess we should backport the fix into -stable. I added this: : This resulted in the kernel hanging up when executing a loop of the form : : 1. fork : 2. mmap : 3. touch memory : 4. read memory : 5. munmmap : : as described in : http://www.gossamer-threads.com/lists/linux/kernel/1348725#1348725 And the problems which the other patches in this series address are pretty deadly as well. Should we backport everything? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>