On Thu, Nov 18, 2021 at 06:20AM -0800, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 42eb8fdac2fc Merge tag 'gfs2-v5.16-rc2-fixes' of git://git.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=13160026b00000 > kernel config: https://syzkaller.appspot.com/x/.config?x=a70237460d215073 > dashboard link: https://syzkaller.appspot.com/bug?extid=aa5bebed695edaccf0df > compiler: Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.2 > > 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+aa5bebed695edaccf0df@xxxxxxxxxxxxxxxxxxxxxxxxx > > ================================================================== > BUG: KCSAN: data-race in flush_tlb_batched_pending / try_to_unmap_one > > write to 0xffff8881072cfbbc of 1 bytes by task 17406 on cpu 1: > flush_tlb_batched_pending+0x5f/0x80 mm/rmap.c:691 > madvise_free_pte_range+0xee/0x7d0 mm/madvise.c:594 > walk_pmd_range mm/pagewalk.c:128 [inline] > walk_pud_range mm/pagewalk.c:205 [inline] > walk_p4d_range mm/pagewalk.c:240 [inline] > walk_pgd_range mm/pagewalk.c:277 [inline] > __walk_page_range+0x981/0x1160 mm/pagewalk.c:379 > walk_page_range+0x131/0x300 mm/pagewalk.c:475 > madvise_free_single_vma mm/madvise.c:734 [inline] > madvise_dontneed_free mm/madvise.c:822 [inline] > madvise_vma mm/madvise.c:996 [inline] > do_madvise+0xe4a/0x1140 mm/madvise.c:1202 > __do_sys_madvise mm/madvise.c:1228 [inline] > __se_sys_madvise mm/madvise.c:1226 [inline] > __x64_sys_madvise+0x5d/0x70 mm/madvise.c:1226 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > write to 0xffff8881072cfbbc of 1 bytes by task 71 on cpu 0: > set_tlb_ubc_flush_pending mm/rmap.c:636 [inline] > try_to_unmap_one+0x60e/0x1220 mm/rmap.c:1515 > rmap_walk_anon+0x2fb/0x470 mm/rmap.c:2301 > try_to_unmap+0xec/0x110 > shrink_page_list+0xe91/0x2620 mm/vmscan.c:1719 > shrink_inactive_list+0x3fb/0x730 mm/vmscan.c:2394 > shrink_list mm/vmscan.c:2621 [inline] > shrink_lruvec+0x3c9/0x710 mm/vmscan.c:2940 > shrink_node_memcgs+0x23e/0x410 mm/vmscan.c:3129 > shrink_node+0x8f6/0x1190 mm/vmscan.c:3252 > kswapd_shrink_node mm/vmscan.c:4022 [inline] > balance_pgdat+0x702/0xd30 mm/vmscan.c:4213 > kswapd+0x200/0x340 mm/vmscan.c:4473 > kthread+0x2c7/0x2e0 kernel/kthread.c:327 > ret_from_fork+0x1f/0x30 > > value changed: 0x01 -> 0x00 > > Reported by Kernel Concurrency Sanitizer on: > CPU: 0 PID: 71 Comm: kswapd0 Not tainted 5.16.0-rc1-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > ================================================================== Reading 3ea277194daae, I can't quite determine if this is safe and expected. Per this observed write/write race, depending on interleaving tlb_flush_batched can randomly be true or false after set_tlb_ubc_flush_pending(). Is this safe? Thanks, -- Marco
