On Tue, Nov 13, 2018 at 08:55:11PM +0000, Roman Gushchin wrote:

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+	if (lock_task_sighand(task, &flags)) {
+		if (test_bit(CGRP_FREEZE, &dst->flags))
+			task->jobctl |= JOBCTL_TRAP_FREEZE;
+		else
+			task->jobctl &= ~JOBCTL_TRAP_FREEZE;

How are these flags synchronized?

Using the css_set_lock.

But other JOBCTL_TRAP bits aren't synchronized by css_set_lock, right?

But if we don't touch this bit anywhere else, should be fine, right?

But other JOBCTL_TRAP_ bits aren't synchronized with css_set_lock, so
they can be updated (read-modify-write) concurrently and clobber each
other, no?

Thanks.

-- 
tejun