On Tue, Jun 23, 2020 at 10:24:04PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 23, 2020 at 08:12:32PM +0200, Peter Zijlstra wrote:
> > Fair enough; I'll rip it all up and boot a KCSAN kernel, see what if
> > anything happens.
>
> OK, so the below patch doesn't seem to have any nasty recursion issues
> here. The only 'problem' is that lockdep now sees report_lock can cause
> deadlocks.
>
> It is completely right about it too, but I don't suspect there's much we
> can do about it, it's pretty much the standard printk() with scheduler
> locks held report.
Just for giggles I added the below and that works fine too. Right until
the report_lock deadlock splat of course, thereafter lockdep is
disabled.
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index ac5f8345bae9..a011cf0a1611 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -459,6 +459,8 @@ static void set_other_info_task_blocking(unsigned long *flags,
*/
int timeout = max(kcsan_udelay_task, kcsan_udelay_interrupt);
+ lockdep_assert_held(&report_lock);
+
other_info->task = current;
do {
if (is_running) {
@@ -495,6 +497,8 @@ static void set_other_info_task_blocking(unsigned long *flags,
other_info->task == current);
if (is_running)
set_current_state(TASK_RUNNING);
+
+ lockdep_assert_held(&report_lock);
}
/* Populate @other_info; requires that the provided @other_info not in use. */
