Commit 248591f5 authored by Marco Elver's avatar Marco Elver Committed by Peter Zijlstra
Browse files

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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200624113246.GA170324@elver.google.com
parent e1bcad60

kernel/kcsan/core.c

+2 −3
Original line number Diff line number Diff line
@@ -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);

}

kernel/kcsan/report.c

+5 −4
Original line number Diff line number Diff line
@@ -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();

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