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Subject[PATCH] kernel: locking: rtmutex: Fix a possible sleep-in-atomic-context bug in rt_mutex_handle_deadlock()
Date
The driver may sleep with holding a spinlock.

The function call paths (from bottom to top) in Linux-4.16 are:

[FUNC] schedule
kernel/locking/rtmutex.c, 1223:
schedule in rt_mutex_handle_deadlock
kernel/locking/rtmutex.c, 1273:
rt_mutex_handle_deadlock in rt_mutex_slowlock
kernel/locking/rtmutex.c, 1249:
_raw_spin_lock_irqsave in rt_mutex_slowlock

To fix the bug, the spinlock is released before schedule() and then acquired again.
This is found by my static analysis tool (DSAC).

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
kernel/locking/rtmutex.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 2823d4163a37..af03e162f812 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1205,7 +1205,7 @@ __rt_mutex_slowlock(struct rt_mutex *lock, int state,
}

static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
- struct rt_mutex_waiter *w)
+ struct rt_mutex_waiter *w, struct rt_mutex *lock)
{
/*
* If the result is not -EDEADLOCK or the caller requested
@@ -1219,8 +1219,10 @@ static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
*/
rt_mutex_print_deadlock(w);
while (1) {
+ raw_spin_unlock_irq(&lock->wait_lock);
set_current_state(TASK_INTERRUPTIBLE);
schedule();
+ raw_spin_lock_irq(&lock->wait_lock);
}
}

@@ -1269,7 +1271,7 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
if (unlikely(ret)) {
__set_current_state(TASK_RUNNING);
remove_waiter(lock, &waiter);
- rt_mutex_handle_deadlock(ret, chwalk, &waiter);
+ rt_mutex_handle_deadlock(ret, chwalk, &waiter, lock);
}

/*
--
2.17.0
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