[+Cc XArray maintainer] Hi Matthew, On Mon, Aug 10, 2020 at 05:41AM -0700, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: fc80c51f Merge tag 'kbuild-v5.9' of git://git.kernel.org/p.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=13cb73fa900000 > kernel config: https://syzkaller.appspot.com/x/.config?x=997a92ee4b5588ef > dashboard link: https://syzkaller.appspot.com/bug?extid=0d4522639ba75b02bf19 > compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b) > > Unfortunately, I don't have any reproducer for this issue yet. > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+0d4522639ba75b02bf19@xxxxxxxxxxxxxxxxxxxxxxxxx > > ================================================================== > BUG: KCSAN: data-race in __xa_clear_mark / xas_find_marked > > write to 0xffff8880bace9b30 of 8 bytes by interrupt on cpu 1: > instrument_write include/linux/instrumented.h:42 [inline] > __test_and_clear_bit include/asm-generic/bitops/instrumented-non-atomic.h:85 [inline] > node_clear_mark lib/xarray.c:100 [inline] > xas_clear_mark lib/xarray.c:908 [inline] > __xa_clear_mark+0x229/0x350 lib/xarray.c:1726 > test_clear_page_writeback+0x28d/0x480 mm/page-writeback.c:2739 > end_page_writeback+0xa7/0x110 mm/filemap.c:1369 > page_endio+0x1aa/0x1e0 mm/filemap.c:1400 > mpage_end_io+0x186/0x1d0 fs/mpage.c:54 > bio_endio+0x28a/0x370 block/bio.c:1447 > req_bio_endio block/blk-core.c:259 [inline] > blk_update_request+0x535/0xbd0 block/blk-core.c:1576 > blk_mq_end_request+0x22/0x50 block/blk-mq.c:562 > lo_complete_rq+0xca/0x180 drivers/block/loop.c:500 > blk_done_softirq+0x1a5/0x200 block/blk-mq.c:586 > __do_softirq+0x198/0x360 kernel/softirq.c:298 > run_ksoftirqd+0x2f/0x60 kernel/softirq.c:652 > smpboot_thread_fn+0x347/0x530 kernel/smpboot.c:165 > kthread+0x20d/0x230 kernel/kthread.c:292 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294 > > read to 0xffff8880bace9b30 of 8 bytes by task 12715 on cpu 0: > xas_find_chunk include/linux/xarray.h:1625 [inline] > xas_find_marked+0x22f/0x6b0 lib/xarray.c:1198 > find_get_pages_range_tag+0xa3/0x580 mm/filemap.c:1976 > pagevec_lookup_range_tag+0x37/0x50 mm/swap.c:1120 > __filemap_fdatawait_range+0xab/0x1b0 mm/filemap.c:519 > filemap_fdatawait_range mm/filemap.c:554 [inline] > filemap_write_and_wait_range+0x119/0x2a0 mm/filemap.c:664 > generic_file_read_iter+0x11d/0x3e0 mm/filemap.c:2375 > call_read_iter include/linux/fs.h:1866 [inline] > generic_file_splice_read+0x22b/0x310 fs/splice.c:312 > do_splice_to fs/splice.c:870 [inline] > splice_direct_to_actor+0x2a8/0x660 fs/splice.c:950 > do_splice_direct+0xf2/0x170 fs/splice.c:1059 > do_sendfile+0x56a/0xba0 fs/read_write.c:1540 > __do_sys_sendfile64 fs/read_write.c:1595 [inline] > __se_sys_sendfile64 fs/read_write.c:1587 [inline] > __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1587 > do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > Reported by Kernel Concurrency Sanitizer on: > CPU: 0 PID: 12715 Comm: syz-executor.4 Not tainted 5.8.0-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > ================================================================== We had a discussion around this earlier this year: https://lore.kernel.org/lkml/20200305151831.GM29971@xxxxxxxxxxxxxxxxxxxxxx/#t where you mentioned: > - If a bit was set before and after the modification, it must be seen to > be set. > - If a bit was clear before and after the modification, it must be seen to > be clear. > - If a bit is modified, it may be seen as set or clear. Do the atomic bitops satisfy those criteria? (Though there were still some issues around find_next_bit(), but maybe we can fix that?) In general, we're wondering what is required to address this properly. [ Note: There are a bunch more syzbot reports, which can be treated as duplicates, and haven't been sent to LKML: https://syzkaller.appspot.com/bug?id=b3f09ccd19880d00592d1692ae3bfe5933fa2b86 https://syzkaller.appspot.com/bug?id=783c9bf4ad668f022c60e9b12bd8ce9974c1512a https://syzkaller.appspot.com/bug?id=711fd5ad665157363e7a21df0c3808884ebeabb9 https://syzkaller.appspot.com/bug?id=cd60a83c9ff17c293fbb51355cf7b2f0420c4e0e https://syzkaller.appspot.com/bug?id=4b16c74b38549b01920b73e5f2df53be5e8dae75 https://syzkaller.appspot.com/bug?id=7df642f4aa1c195834b4687ed3a9f18cd7f12ae8 ] Thanks, -- Marco
