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.
---
diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index 15f67949d11e..732623c30359 100644
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -397,8 +397,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
}
if (!kcsan_interrupt_watcher)
- /* Use raw to avoid lockdep recursion via IRQ flags tracing. */
- raw_local_irq_save(irq_flags);
+ local_irq_save(irq_flags);
watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write);
if (watchpoint == NULL) {
@@ -539,7 +538,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS);
out_unlock:
if (!kcsan_interrupt_watcher)
- raw_local_irq_restore(irq_flags);
+ local_irq_restore(irq_flags);
out:
user_access_restore(ua_flags);
}
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index ac5f8345bae9..ef31c1d2dac3 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -605,14 +605,6 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type,
if (WARN_ON(watchpoint_idx < 0 || watchpoint_idx >= ARRAY_SIZE(other_infos)))
goto out;
- /*
- * With TRACE_IRQFLAGS, lockdep's IRQ trace state becomes corrupted if
- * we do not turn off lockdep here; this could happen due to recursion
- * into lockdep via KCSAN if we detect a race in utilities used by
- * lockdep.
- */
- lockdep_off();
-
if (prepare_report(&flags, type, &ai, other_info)) {
/*
* Never report if value_change is FALSE, only if we it is
@@ -628,7 +620,6 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type,
release_report(&flags, other_info);
}
- lockdep_on();
out:
kcsan_enable_current();
}
