kcsan: Make KCSAN compatible with new IRQ state tracking

The new IRQ state tracking code does not honor lockdep_off(), and as
such we should again permit tracing by using non-raw functions in
core.c. Update the lockdep_off() comment in report.c, to reflect the
fact there is still a potential risk of deadlock due to using printk()
from scheduler code.

Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200624113246.GA170324@elver.google.com

diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index 15f6794..732623c 100644 (file)
--- 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 ac5f834..6b2fb1a 100644 (file)
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -606,10 +606,11 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type,
                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.
+        * Because we may generate reports when we're in scheduler code, the use
+        * of printk() could deadlock. Until such time that all printing code
+        * called in print_report() is scheduler-safe, accept the risk, and just
+        * get our message out. As such, also disable lockdep to hide the
+        * warning, and avoid disabling lockdep for the rest of the kernel.
         */
        lockdep_off();