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SJ2PR12MB8847 On 24 Sep 2025, at 7:32, David Hildenbrand wrote: > On 23.09.25 18:22, syzbot wrote: >> Hello, >> >> syzbot found the following issue on: >> >> HEAD commit: b5db4add5e77 Merge branch 'for-next/core' into for-ker= nelci >> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/li= nux.git for-kernelci >> console output: https://syzkaller.appspot.com/x/log.txt?x=3D10edb8e258= 0000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=3Dd2ae34a071= 1ff2f1 >> dashboard link: https://syzkaller.appspot.com/bug?extid=3De6367ea2fdab= 6ed46056 >> compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b= 7976-1~exp1~20250708183702.136), Debian LLD 20.1.8 >> userspace arch: arm64 >> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=3D14160f12= 580000 >> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=3D1361627c58= 0000 >> >> Downloadable assets: >> disk image: https://storage.googleapis.com/syzbot-assets/6eee2232d5c1/= disk-b5db4add.raw.xz >> vmlinux: https://storage.googleapis.com/syzbot-assets/a8b00f2f1234/vml= inux-b5db4add.xz >> kernel image: https://storage.googleapis.com/syzbot-assets/fc0d466f156= c/Image-b5db4add.gz.xz >> >> IMPORTANT: if you fix the issue, please add the following tag to the c= ommit: >> Reported-by: syzbot+e6367ea2fdab6ed46056@syzkaller.appspotmail.com >> >> Injecting memory failure for pfn 0x104000 at process virtual address 0= x20000000 >> ------------[ cut here ]------------ >> WARNING: CPU: 1 PID: 6700 at mm/memory-failure.c:2391 memory_failure+0= x18ec/0x1db4 mm/memory-failure.c:2391 >> Modules linked in: >> CPU: 1 UID: 0 PID: 6700 Comm: syz.0.17 Not tainted syzkaller #0 PREEMP= T >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIO= S Google 06/30/2025 >> pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=3D--) >> pc : memory_failure+0x18ec/0x1db4 mm/memory-failure.c:2391 >> lr : memory_failure+0x18ec/0x1db4 mm/memory-failure.c:2391 >> sp : ffff8000a41478c0 >> x29: ffff8000a41479a0 x28: 05ffc00000200868 x27: ffff700014828f20 >> x26: 1fffffbff8620001 x25: 05ffc0000020086d x24: 1fffffbff8620000 >> x23: fffffdffc3100008 x22: fffffdffc3100000 x21: fffffdffc3100000 >> x20: 0000000000000023 x19: dfff800000000000 x18: 1fffe00033793888 >> x17: ffff80008f7ee000 x16: ffff80008052aa64 x15: 0000000000000001 >> x14: 1fffffbff8620000 x13: 0000000000000000 x12: 0000000000000000 >> x11: ffff7fbff8620001 x10: 0000000000ff0100 x9 : 0000000000000000 >> x8 : ffff0000d7eedb80 x7 : ffff800080428910 x6 : 0000000000000000 >> x5 : 0000000000000001 x4 : 0000000000000001 x3 : ffff800080cf5438 >> x2 : 0000000000000001 x1 : 0000000000000040 x0 : 0000000000000000 >> Call trace: >> memory_failure+0x18ec/0x1db4 mm/memory-failure.c:2391 (P) >> madvise_inject_error mm/madvise.c:1475 [inline] >> madvise_do_behavior+0x2c8/0x7c4 mm/madvise.c:1875 >> do_madvise+0x190/0x248 mm/madvise.c:1978 >> __do_sys_madvise mm/madvise.c:1987 [inline] >> __se_sys_madvise mm/madvise.c:1985 [inline] >> __arm64_sys_madvise+0xa4/0xc0 mm/madvise.c:1985 >> __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] >> invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49 >> el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132 >> do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151 >> el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:744 >> el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:763= >> el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596 > > We're running into the > > WARN_ON(folio_test_large(folio)); > > in memory_failure(). > > Which is weird because we have the > > if (folio_test_large(folio)) { > /* > * The flag must be set after the refcount is bumped > * otherwise it may race with THP split. > * And the flag can't be set in get_hwpoison_page() sin= ce > * it is called by soft offline too and it is just call= ed > * for !MF_COUNT_INCREASED. So here seems to be the be= st > * place. > * > * Don't need care about the above error handling paths= for > * get_hwpoison_page() since they handle either free pa= ge > * or unhandlable page. The refcount is bumped iff the= > * page is a valid handlable page. > */ > folio_set_has_hwpoisoned(folio); > if (try_to_split_thp_page(p, false) < 0) { > res =3D -EHWPOISON; > kill_procs_now(p, pfn, flags, folio); > put_page(p); > action_result(pfn, MF_MSG_UNSPLIT_THP, MF_FAILE= D); > goto unlock_mutex; > } > VM_BUG_ON_PAGE(!page_count(p), p); > folio =3D page_folio(p); > } > > before it. > > But likely that's what I raised to Zi Yan recently: if try_to_split_thp= _page()->split_huge_page() > silently decided to split to something that is not a small folio (the m= in_order_for_split() bit), > this changed the semantics of the function. > > Likely split_huge_page() should have failed if the min_order makes us n= ot split to order-0, > or there would have to be some "parameter" that tells split_huge_page()= what expectation (order) the > callers has. > > We can check folio_test_large() after the split, but really, we should = just not be splitting at > all if it doesn't serve our purpose. But LBS might want to split from a high order to fs min_order. What I can think of is: 0. split code always does a split to allowed minimal order, namely max(fs_min_order, order_from_caller); 1. if split order cannot reach to order_from_caller, it just return fails= , so most of the caller will know about it; 2. for LBS code, when it sees a split failure, it should check the result= ing folio order against fs min_order. If the orders match, it regards it a= s a success. At least, most of the code does not need to be LBS aware. WDYT? Best Regards, Yan, Zi