Messages in this thread | | | Date | Tue, 31 Aug 2021 14:13:14 +0100 | From | Will Deacon <> | Subject | Re: [mm] f9ce0be71d: BUG:KCSAN:data-race_in_next_uptodate_page/next_uptodate_page |
| |
[+Marco]
On Fri, Aug 27, 2021 at 06:42:32PM +0300, Kirill A. Shutemov wrote: > On Thu, Aug 26, 2021 at 10:41:57PM +0800, kernel test robot wrote: > > commit: f9ce0be71d1fbb038ada15ced83474b0e63f264d ("mm: Cleanup faultaround and finish_fault() codepaths") > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master > > > > in testcase: trinity > > version: > > with following parameters: > > > > number: 99999 > > group: group-04 > > > > test-description: Trinity is a linux system call fuzz tester. > > test-url: http://codemonkey.org.uk/projects/trinity/ > > > > > > on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G > > > > caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace): > > > > +------------------------------------------------------------------------+-----------+------------+ > > | | v5.11-rc4 | f9ce0be71d | > > +------------------------------------------------------------------------+-----------+------------+ > > | BUG:KCSAN:data-race_in_next_uptodate_page/next_uptodate_page | 0 | 19 | > > | BUG:KCSAN:data-race_in_mark_page_accessed/next_uptodate_page | 0 | 17 | > > | BUG:KCSAN:data-race_in_next_uptodate_page/page_memcg | 0 | 13 | > > | BUG:KCSAN:data-race_in_next_uptodate_page/unlock_page | 0 | 13 | > > +------------------------------------------------------------------------+-----------+------------+ > > > > [ 184.717904][ T1873] ================================================================== > > [ 184.718938][ T1873] BUG: KCSAN: data-race in next_uptodate_page / unlock_page > > [ 184.719828][ T1873] > > [ 184.720103][ T1873] write (marked) to 0xffffea00050f37c0 of 8 bytes by task 1872 on cpu 1: > > [ 184.721024][ T1873] unlock_page+0x102/0x1b0 > > [ 184.721533][ T1873] filemap_map_pages+0x6c6/0x890 > > [ 184.722102][ T1873] handle_mm_fault+0x179c/0x27f0 > > [ 184.722672][ T1873] do_user_addr_fault+0x3fb/0x830 > > [ 184.723263][ T1873] exc_page_fault+0xc3/0x1a0 > > [ 184.723845][ T1873] asm_exc_page_fault+0x1e/0x30 > > [ 184.724427][ T1873] > > [ 184.724720][ T1873] read to 0xffffea00050f37c0 of 8 bytes by task 1873 on cpu 0: > > [ 184.725575][ T1873] next_uptodate_page+0x456/0x830 > > [ 184.726161][ T1873] filemap_map_pages+0x728/0x890 > > [ 184.726747][ T1873] handle_mm_fault+0x179c/0x27f0 > > [ 184.727332][ T1873] do_user_addr_fault+0x3fb/0x830 > > [ 184.727905][ T1873] exc_page_fault+0xc3/0x1a0 > > [ 184.728440][ T1873] asm_exc_page_fault+0x1e/0x30 > > [ 184.729027][ T1873] > > [ 184.729313][ T1873] Reported by Kernel Concurrency Sanitizer on: > > [ 184.730019][ T1873] CPU: 0 PID: 1873 Comm: systemd-udevd Not tainted 5.11.0-rc4-00001-gf9ce0be71d1f #1 > > [ 184.731103][ T1873] ================================================================== > > Line annotation would be helpful.
Agreed.
> And I'm not very familiar with KCSAN. My guess it reports PageLock() vs. > clearing PG_locked. In this context it looks safe, unless I miss > something.
The access in clear_bit_unlock() is annotated as a full sizeof(long) atomic write, so we could be racing with a non-atomic read of another bit in the page flags but I can't spot where that happens before the trylock_page() in next_uptodate_page().
> Do we need some annotation to help KCSAN?
clear_bit_unlock() is already instrumented and _most_ of the helpers in page-flags.h look they should be as well by virtue of using test_bit().
Will
| |