From: Peng Liu <liupeng256@xxxxxxxxxx> Subject: mm/mmap.c: fix a data race of mm->total_vm Variable mm->total_vm could be accessed concurrently during mmaping and system accounting as noticed by KCSAN, BUG: KCSAN: data-race in __acct_update_integrals / mmap_region read-write to 0xffffa40267bd14c8 of 8 bytes by task 15609 on cpu 3: mmap_region+0x6dc/0x1400 do_mmap+0x794/0xca0 vm_mmap_pgoff+0xdf/0x150 ksys_mmap_pgoff+0xe1/0x380 do_syscall_64+0x37/0x50 entry_SYSCALL_64_after_hwframe+0x44/0xa9 read to 0xffffa40267bd14c8 of 8 bytes by interrupt on cpu 2: __acct_update_integrals+0x187/0x1d0 acct_account_cputime+0x3c/0x40 update_process_times+0x5c/0x150 tick_sched_timer+0x184/0x210 __run_hrtimer+0x119/0x3b0 hrtimer_interrupt+0x350/0xaa0 __sysvec_apic_timer_interrupt+0x7b/0x220 asm_call_irq_on_stack+0x12/0x20 sysvec_apic_timer_interrupt+0x4d/0x80 asm_sysvec_apic_timer_interrupt+0x12/0x20 smp_call_function_single+0x192/0x2b0 perf_install_in_context+0x29b/0x4a0 __se_sys_perf_event_open+0x1a98/0x2550 __x64_sys_perf_event_open+0x63/0x70 do_syscall_64+0x37/0x50 entry_SYSCALL_64_after_hwframe+0x44/0xa9 Reported by Kernel Concurrency Sanitizer on: CPU: 2 PID: 15610 Comm: syz-executor.3 Not tainted 5.10.0+ #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 In vm_stat_account which called by mmap_region, increase total_vm, and __acct_update_integrals may read total_vm at the same time. This will cause a data race which lead to undefined behaviour. To avoid potential bad read/write, volatile property and barrier are both used to avoid undefined behaviour. Link: https://lkml.kernel.org/r/20210913105550.1569419-1-liupeng256@xxxxxxxxxx Signed-off-by: Peng Liu <liupeng256@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/tsacct.c | 2 +- mm/mmap.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) --- a/kernel/tsacct.c~mm-mmapc-fix-a-data-race-of-mm-total_vm +++ a/kernel/tsacct.c @@ -137,7 +137,7 @@ static void __acct_update_integrals(stru * the rest of the math is done in xacct_add_tsk. */ tsk->acct_rss_mem1 += delta * get_mm_rss(tsk->mm) >> 10; - tsk->acct_vm_mem1 += delta * tsk->mm->total_vm >> 10; + tsk->acct_vm_mem1 += delta * READ_ONCE(tsk->mm->total_vm) >> 10; } /** --- a/mm/mmap.c~mm-mmapc-fix-a-data-race-of-mm-total_vm +++ a/mm/mmap.c @@ -3332,7 +3332,7 @@ bool may_expand_vm(struct mm_struct *mm, void vm_stat_account(struct mm_struct *mm, vm_flags_t flags, long npages) { - mm->total_vm += npages; + WRITE_ONCE(mm->total_vm, READ_ONCE(mm->total_vm)+npages); if (is_exec_mapping(flags)) mm->exec_vm += npages; _
