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Subject[PATCH] lockdep: Don't access the hrtimer after the callback
A hrtimer can be released in its callback as reported by syzbot.

Retrieve the context in which the hrtimer expires before its callback is
invoked and use it in lockdep_hrtimer_exit().

Reported-by: syzbot+62c155c276e580cfb606@syzkaller.appspotmail.com
Fixes: 40db173965c0 ("lockdep: Add hrtimer context tracing bits")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
include/linux/irqflags.h | 22 +++++++++++++---------
kernel/time/hrtimer.c | 5 +++--
2 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index a16adbb58f66a..808d10de852f9 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -58,16 +58,20 @@ do { \
} while (0)

# define lockdep_hrtimer_enter(__hrtimer) \
- do { \
- if (!__hrtimer->is_hard) \
- current->irq_config = 1; \
- } while (0)
+({ \
+ bool __expires_hardirq = true; \
+ if (!__hrtimer->is_hard) { \
+ current->irq_config = 1; \
+ __expires_hardirq = false; \
+ } \
+ __expires_hardirq; \
+})

-# define lockdep_hrtimer_exit(__hrtimer) \
- do { \
- if (!__hrtimer->is_hard) \
+# define lockdep_hrtimer_exit(__expires_hardirq) \
+ do { \
+ if (__expires_hardirq == false) \
current->irq_config = 0; \
- } while (0)
+ } while (0)

# define lockdep_posixtimer_enter() \
do { \
@@ -102,7 +106,7 @@ do { \
# define trace_hardirq_exit() do { } while (0)
# define lockdep_softirq_enter() do { } while (0)
# define lockdep_softirq_exit() do { } while (0)
-# define lockdep_hrtimer_enter(__hrtimer) do { } while (0)
+# define lockdep_hrtimer_enter(__hrtimer) false
# define lockdep_hrtimer_exit(__hrtimer) do { } while (0)
# define lockdep_posixtimer_enter() do { } while (0)
# define lockdep_posixtimer_exit() do { } while (0)
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 8cce72501aea5..817a9c7be47e3 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1481,6 +1481,7 @@ static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base,
{
enum hrtimer_restart (*fn)(struct hrtimer *);
int restart;
+ bool expires_in_hardirq;

lockdep_assert_held(&cpu_base->lock);

@@ -1514,11 +1515,11 @@ static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base,
*/
raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
trace_hrtimer_expire_entry(timer, now);
- lockdep_hrtimer_enter(timer);
+ expires_in_hardirq = lockdep_hrtimer_enter(timer);

restart = fn(timer);

- lockdep_hrtimer_exit(timer);
+ lockdep_hrtimer_exit(expires_in_hardirq);
trace_hrtimer_expire_exit(timer);
raw_spin_lock_irq(&cpu_base->lock);

--
2.26.0
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