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 B75cVBkm 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6 Feb 2026, at 17:37, Mikhail Gavrilov wrote: > On Sat, Feb 7, 2026 at 3:16 AM Mikhail Gavrilov > wrote: >> >> Hi Zi, >> Thanks for the deep investigation! >> So the actual culprit is KASAN's kasan_save_stack() leaving non-zero >> page->private. >> That explains why it only reproduces with KASAN enabled. >> Looking at the code, kasan_save_stack() doesn't seem to use >> page->private directly - it goes through stack_depot. Is stack_depot >> the actual culprit? >> Happy to help investigate further if needed. >> Regarding the fix location - even if we fix KASAN/stack_depot, >> split_page() clearing page->private still seems like the right >> defensive fix. >> The contract for split_page() is that it produces independent usable >> pages, and page->private being clean is part of that. >> Other code could potentially leave stale values too. >> I can share my .config if still needed, but it sounds like you've >> already reproduced it. >> > > I think I found it. Looking at mm/internal.h:811, prep_compound_tail() > clears page->private for tail pages, > but it's only called for compound pages (__GFP_COMP). > Before commit 3b8000ae185c, vmalloc used __GFP_COMP, so tail pages got > their page->private cleared via prep_compound_tail(). > After that commit dropped __GFP_COMP, tail pages keep stale values > from buddy allocator (which uses page->private for order). > So the stale value comes from buddy allocator's set_buddy_order() at > mm/page_alloc.c:755, > and __del_page_from_free_list() at line 898 only clears the head page's private. set_buddy_order() also only set head page’s private. And at each buddy page merge, any buddy found in free list gets its head page’s private cleared in __del_page_from_free_list(). The final merged free page gets its private set by set_buddy_order() at done_merging. There should not be any stale values in any page’s private, if I read the code correctly. If it is the problem of buddy allocator leaving stale private values, the problem would be reproducible with and without KASAN. > This confirms the split_page() fix is the right place - it ensures > tail pages are properly initialized for independent use after > splitting. > > -- > Best Regards, > Mike Gavrilov. Best Regards, Yan, Zi