On 6/9/26 20:10, Andrew Morton wrote: > On Tue, 9 Jun 2026 06:12:49 -0400 "Michael S. Tsirkin" <[email protected]> > wrote: > >> TestSetPageHWPoison() is called without zone->lock, so its atomic >> update to page->flags can race with non-atomic flag operations >> that run under zone->lock in the buddy allocator. >> >> In particular, __free_pages_prepare() does: >> >> page->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP; >> >> This non-atomic read-modify-write, while correctly excluding >> __PG_HWPOISON from the mask, can still lose a concurrent >> TestSetPageHWPoison if the read happens before the poison bit >> is set and the write happens after. Will only get worse if/when >> we add more non-atomic flag operations. >> >> Fix by acquiring zone->lock around TestSetPageHWPoison and >> around ClearPageHWPoison in the retry path. This >> serializes with all buddy flag manipulation. The cost is >> negligible: one lock/unlock in an extremely rare path >> (hardware memory errors). >> >> Note: SetPageHWPoison and TestClearPageHWPoison calls elsewhere >> in this file operate on pages already removed from the buddy >> allocator or on non-buddy pages (DAX, hugetlb), so they do not >> need zone->lock protection. > > Sashiko is saying this doesn't do anything "Because > __free_pages_prepare() executes entirely locklessly". Did it goof? > > https://sashiko.dev/#/patchset/df06b66fe4ff8e925ee0714955abc2183a727b90.1780998980.git....@redhat.com
Battle of the bots: it's right. -- Cheers, David
