From: Qian Cai <cai@xxxxxx> Subject: mm/rmap: annotate a data race at tlb_flush_batched mm->tlb_flush_batched could be accessed concurrently as noticed by KCSAN, BUG: KCSAN: data-race in flush_tlb_batched_pending / try_to_unmap_one write to 0xffff93f754880bd0 of 1 bytes by task 822 on cpu 6: try_to_unmap_one+0x59a/0x1ab0 set_tlb_ubc_flush_pending at mm/rmap.c:635 (inlined by) try_to_unmap_one at mm/rmap.c:1538 rmap_walk_anon+0x296/0x650 rmap_walk+0xdf/0x100 try_to_unmap+0x18a/0x2f0 shrink_page_list+0xef6/0x2870 shrink_inactive_list+0x316/0x880 shrink_lruvec+0x8dc/0x1380 shrink_node+0x317/0xd80 balance_pgdat+0x652/0xd90 kswapd+0x396/0x8d0 kthread+0x1e0/0x200 ret_from_fork+0x27/0x50 read to 0xffff93f754880bd0 of 1 bytes by task 6364 on cpu 4: flush_tlb_batched_pending+0x29/0x90 flush_tlb_batched_pending at mm/rmap.c:682 change_p4d_range+0x5dd/0x1030 change_pte_range at mm/mprotect.c:44 (inlined by) change_pmd_range at mm/mprotect.c:212 (inlined by) change_pud_range at mm/mprotect.c:240 (inlined by) change_p4d_range at mm/mprotect.c:260 change_protection+0x222/0x310 change_prot_numa+0x3e/0x60 task_numa_work+0x219/0x350 task_work_run+0xed/0x140 prepare_exit_to_usermode+0x2cc/0x2e0 ret_from_intr+0x32/0x42 Reported by Kernel Concurrency Sanitizer on: CPU: 4 PID: 6364 Comm: mtest01 Tainted: G W L 5.5.0-next-20200210+ #5 Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 flush_tlb_batched_pending() is under PTL but the write is not, but mm->tlb_flush_batched is only a bool type, so the value is unlikely to be shattered. Thus, mark it as an intentional data race by using the data race macro. Link: http://lkml.kernel.org/r/1581450783-8262-1-git-send-email-cai@xxxxxx Signed-off-by: Qian Cai <cai@xxxxxx> Cc: Marco Elver <elver@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/rmap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/rmap.c~mm-rmap-annotate-a-data-race-at-tlb_flush_batched +++ a/mm/rmap.c @@ -672,7 +672,7 @@ static bool should_defer_flush(struct mm */ void flush_tlb_batched_pending(struct mm_struct *mm) { - if (mm->tlb_flush_batched) { + if (data_race(mm->tlb_flush_batched)) { flush_tlb_mm(mm); /* _
