[PATCH linux-next] kernel/fork.c: annotate data races for copy_process

[Weilong Chen]

The check is only there to stop root fork bombs.

BUG: KCSAN: data-race in copy_process / copy_process

write to 0xffffffff86f87d20 of 4 bytes by task 7121 on cpu 5:
 copy_process+0x2e1a/0x3af0 kernel/fork.c:2285
 _do_fork+0xf7/0x790 kernel/fork.c:2430
 __do_sys_clone+0xf9/0x130 kernel/fork.c:2585
 __se_sys_clone kernel/fork.c:2566 [inline]
 __x64_sys_clone+0x6c/0x80 kernel/fork.c:2566
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffffff86f87d20 of 4 bytes by task 7125 on cpu 3:
 copy_process+0x9eb/0x3af0 kernel/fork.c:1967
 _do_fork+0xf7/0x790 kernel/fork.c:2430
 __do_sys_clone+0xf9/0x130 kernel/fork.c:2585
 __se_sys_clone kernel/fork.c:2566 [inline]
 __x64_sys_clone+0x6c/0x80 kernel/fork.c:2566
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Signed-off-by: Weilong Chen <chenweilong@xxxxxxxxxx>
---
 kernel/fork.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 142b23645d82..efc5493203ae 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1977,7 +1977,7 @@ static __latent_entropy struct task_struct *copy_process(
 	 * to stop root fork bombs.
 	 */
 	retval = -EAGAIN;
-	if (nr_threads >= max_threads)
+	if (data_race(nr_threads >= max_threads))
 		goto bad_fork_cleanup_count;
 
 	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */
-- 
2.17.1