"vm_committed_as.count" could be accessed concurrently as reported by KCSAN, BUG: KCSAN: data-race in __vm_enough_memory / percpu_counter_add_batch write to 0xffffffff9451c538 of 8 bytes by task 65879 on cpu 35: percpu_counter_add_batch+0x83/0xd0 percpu_counter_add_batch at lib/percpu_counter.c:91 __vm_enough_memory+0xb9/0x260 dup_mm+0x3a4/0x8f0 copy_process+0x2458/0x3240 _do_fork+0xaa/0x9f0 __do_sys_clone+0x125/0x160 __x64_sys_clone+0x70/0x90 do_syscall_64+0x91/0xb05 entry_SYSCALL_64_after_hwframe+0x49/0xbe read to 0xffffffff9451c538 of 8 bytes by task 66773 on cpu 19: __vm_enough_memory+0x199/0x260 percpu_counter_read_positive at include/linux/percpu_counter.h:81 (inlined by) __vm_enough_memory at mm/util.c:839 mmap_region+0x1b2/0xa10 do_mmap+0x45c/0x700 vm_mmap_pgoff+0xc0/0x130 ksys_mmap_pgoff+0x6e/0x300 __x64_sys_mmap+0x33/0x40 do_syscall_64+0x91/0xb05 entry_SYSCALL_64_after_hwframe+0x49/0xbe The read is outside percpu_counter::lock critical section which results in a data race. Fix it by adding a READ_ONCE() in percpu_counter_read_positive() which could also service as the existing compiler memory barrier.
Unified · Split
| @@ -78,9 +78,9 @@ static inline s64 percpu_counter_read(struct percpu_counter *fbc) · 77 unmodified lines | |||
| 78 | */ | 78 | */ |
| 79 | static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc) | 79 | static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc) |
| 80 | { | 80 | { |
| 81 | s64 ret = fbc->count; | 81 | /* Prevent reloads of fbc->count */ |
| 82 | s64 ret = READ_ONCE(fbc->count); | ||
| 82 | 83 | ||
| 83 | barrier(); /* Prevent reloads of fbc->count */ | ||
| 84 | if (ret >= 0) | 84 | if (ret >= 0) |
| 85 | return ret; | 85 | return ret; |
| 86 | return 0; | 86 | return 0; |