On Thu, Sep 17, 2020 at 10:10:43AM +0200, Oscar Salvador wrote: > The crux of the matter is that historically we left poisoned pages in the > buddy system because we have some checks in place when allocating a page > that a gatekeeper for poisoned pages. Unfortunately, we do have other > users (e.g: compaction [1]) that scan buddy freelists and try to get a > page from there without checking whether the page is HWPoison. > > As I stated already, I think it is fundamentally wrong to keep HWPoison > pages within the buddy systems, checks in place or not. > > Let us fix this we same way we did for soft_offline [2], and take the page > off the buddy freelist, so it is completely unreachable. > > Note that this is fairly simple to trigger, as we only need to poison free > buddy pages (madvise MADV_HWPOISON) and then we need to run some sort of > memory stress system. > > Just for a matter of reference, I put a dump_page in compaction_alloc to > trigger for HWPoison patches: > > kernel: page:0000000012b2982b refcount:1 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x1d5db > kernel: flags: 0xfffffc0800000(hwpoison) > kernel: raw: 000fffffc0800000 ffffea00007573c8 ffffc90000857de0 0000000000000000 > kernel: raw: 0000000000000001 0000000000000000 00000001ffffffff 0000000000000000 > kernel: page dumped because: compaction_alloc > > kernel: CPU: 4 PID: 123 Comm: kcompactd0 Tainted: G E 5.9.0-rc2-mm1-1-default+ #5 > kernel: Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014 > kernel: Call Trace: > kernel: dump_stack+0x6d/0x8b > kernel: compaction_alloc+0xb2/0xc0 > kernel: migrate_pages+0x2a6/0x12a0 > kernel: ? isolate_freepages+0xc80/0xc80 > kernel: ? __ClearPageMovable+0xb0/0xb0 > kernel: compact_zone+0x5eb/0x11c0 > kernel: ? finish_task_switch+0x74/0x300 > kernel: ? lock_timer_base+0xa8/0x170 > kernel: proactive_compact_node+0x89/0xf0 > kernel: ? kcompactd+0x2d0/0x3a0 > kernel: kcompactd+0x2d0/0x3a0 > kernel: ? finish_wait+0x80/0x80 > kernel: ? kcompactd_do_work+0x350/0x350 > kernel: kthread+0x118/0x130 > kernel: ? kthread_associate_blkcg+0xa0/0xa0 > kernel: ret_from_fork+0x22/0x30 > > After that, if e.g: someone faults in the page, that someone will get > killed unexpectedly. > > While we are at it, I also changed the action result for such cases. > I think that MF_DELAYED is a bit misleading, because in case we could > contain the page and take it off the buddy, such a page is not to be used > again unless it is unpoisoned, so we fixed the situation. > > So unless I am missing something, I strongly think that we should report > MF_RECOVERED. > > [1] https://lore.kernel.org/linux-mm/20190826104144.GA7849@linux/T/#u > [2] https://patchwork.kernel.org/patch/11694847/ > > Signed-off-by: Oscar Salvador <osalvador@xxxxxxx> Acked-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
