On Tue, 22 Oct 2019 15:44:12 -0700 syzbot <syzbot+667740df862911577d63@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > Hello, > > syzbot found the following crash on: > > HEAD commit: a722f75b Add linux-next specific files for 20191022 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=126aea5b600000 > kernel config: https://syzkaller.appspot.com/x/.config?x=32434321999f01e9 > dashboard link: https://syzkaller.appspot.com/bug?extid=667740df862911577d63 > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > Unfortunately, I don't have any reproducer for this crash yet. > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+667740df862911577d63@xxxxxxxxxxxxxxxxxxxxxxxxx > > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 1080 at mm/khugepaged.c:1643 > collapse_file+0x1f9d/0x4170 mm/khugepaged.c:1643 > Kernel panic - not syncing: panic_on_warn set ... > CPU: 1 PID: 1080 Comm: khugepaged Not tainted 5.4.0-rc4-next-20191022 #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x172/0x1f0 lib/dump_stack.c:113 > panic+0x2e3/0x75c kernel/panic.c:221 > __warn.cold+0x2f/0x35 kernel/panic.c:582 > report_bug+0x289/0x300 lib/bug.c:195 > fixup_bug arch/x86/kernel/traps.c:174 [inline] > fixup_bug arch/x86/kernel/traps.c:169 [inline] > do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:267 > do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:286 > invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027 > RIP: 0010:collapse_file+0x1f9d/0x4170 mm/khugepaged.c:1643 > Code: a1 c0 ff 31 c9 ba 01 00 00 00 4c 89 fe 48 8b bd c0 fe ff ff e8 e4 e9 > ec ff e9 b4 fd ff ff 4c 8b bd 88 fe ff ff e8 93 a1 c0 ff <0f> 0b 4c 8b a3 > 50 ff ff ff c7 85 80 fe ff ff 00 00 00 00 e9 05 f6 > RSP: 0018:ffff8880a818fad0 EFLAGS: 00010293 > RAX: ffff8880a7dd8440 RBX: ffff8880a818fc88 RCX: ffffffff81b2b688 > RDX: 0000000000000000 RSI: ffffffff81b2b9ad RDI: 0000000000000001 > RBP: ffff8880a818fcb0 R08: ffff8880a7dd8440 R09: fffff940004942b9 > R10: fffff940004942b8 R11: ffffea00024a15c7 R12: 0000000000000001 > R13: ffffea0002383a08 R14: 0000000000000000 R15: ffffea0002338000 > khugepaged_scan_file mm/khugepaged.c:1881 [inline] > khugepaged_scan_mm_slot mm/khugepaged.c:1979 [inline] > khugepaged_do_scan mm/khugepaged.c:2063 [inline] > khugepaged+0x2da9/0x4360 mm/khugepaged.c:2108 > kthread+0x361/0x430 kernel/kthread.c:255 > ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352 Thanks. This should be fixed in v4: From: Song Liu <songliubraving@xxxxxx> Subject: mmthp-recheck-each-page-before-collapsing-file-thp-v4 Trigger filemap_flush() for PageDirty() case. This covers one-off situation, where the file hasn't been flushed since first write. Link: http://lkml.kernel.org/r/20191022191006.411277-1-songliubraving@xxxxxx Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") Signed-off-by: Song Liu <songliubraving@xxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: William Kucharski <william.kucharski@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/khugepaged.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) --- a/mm/khugepaged.c~mmthp-recheck-each-page-before-collapsing-file-thp-v4 +++ a/mm/khugepaged.c @@ -1636,11 +1636,20 @@ static void collapse_file(struct mm_stru goto out_unlock; } - /* - * khugepaged should not try to collapse dirty pages for - * file THP. Show warning if this somehow happens. - */ - if (WARN_ON_ONCE(!is_shmem && PageDirty(page))) { + if (!is_shmem && PageDirty(page)) { + /* + * khugepaged only works on read-only fd, so this + * page is dirty because it hasn't been flushed + * since first write. There won't be new dirty + * pages. + * + * Trigger async flush here and hope the writeback + * is done when khugepaged revisits this page. + * + * This is a one-off situation. We are not forcing + * writeback in loop. + */ + filemap_flush(mapping); result = SCAN_FAIL; goto out_unlock; } _
