From: Qian Cai cai@lca.pw
[ Upstream commit 7e2345200262e4a6056580f0231cccdaffc825f3 ]
"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.
Signed-off-by: Qian Cai cai@lca.pw Signed-off-by: Andrew Morton akpm@linux-foundation.org Acked-by: Marco Elver elver@google.com Link: http://lkml.kernel.org/r/1582302724-2804-1-git-send-email-cai@lca.pw Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/percpu_counter.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h index 84a1094496100..b6332cb761a4c 100644 --- a/include/linux/percpu_counter.h +++ b/include/linux/percpu_counter.h @@ -76,9 +76,9 @@ static inline s64 percpu_counter_read(struct percpu_counter *fbc) */ static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc) { - s64 ret = fbc->count; + /* Prevent reloads of fbc->count */ + s64 ret = READ_ONCE(fbc->count);
- barrier(); /* Prevent reloads of fbc->count */ if (ret >= 0) return ret; return 0;