Re: [PATCH] semaphore: Add might_sleep() to down_*() family

From: Waiman Long
Date: Sun Aug 08 2021 - 23:01:26 EST


On 8/8/21 10:12 PM, Xiaoming Ni wrote:
Semaphore is sleeping lock. Add might_sleep() to down*() family
(with exception of down_trylock()) to detect atomic context sleep.

Previously discussed with Peter Zijlstra, see link:
https://lore.kernel.org/lkml/20210806082320.GD22037@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Signed-off-by: Xiaoming Ni <nixiaoming@xxxxxxxxxx>
---
kernel/locking/semaphore.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c
index 9aa855a96c4a..9ee381e4d2a4 100644
--- a/kernel/locking/semaphore.c
+++ b/kernel/locking/semaphore.c
@@ -54,6 +54,7 @@ void down(struct semaphore *sem)
{
unsigned long flags;
+ might_sleep();
raw_spin_lock_irqsave(&sem->lock, flags);
if (likely(sem->count > 0))
sem->count--;
@@ -77,6 +78,7 @@ int down_interruptible(struct semaphore *sem)
unsigned long flags;
int result = 0;
+ might_sleep();
raw_spin_lock_irqsave(&sem->lock, flags);
if (likely(sem->count > 0))
sem->count--;
@@ -103,6 +105,7 @@ int down_killable(struct semaphore *sem)
unsigned long flags;
int result = 0;
+ might_sleep();
raw_spin_lock_irqsave(&sem->lock, flags);
if (likely(sem->count > 0))
sem->count--;
@@ -157,6 +160,7 @@ int down_timeout(struct semaphore *sem, long timeout)
unsigned long flags;
int result = 0;
+ might_sleep();
raw_spin_lock_irqsave(&sem->lock, flags);
if (likely(sem->count > 0))
sem->count--;

I think it is simpler to just put a "might_sleep()" in __down_common() which is the function where sleep can actually happen.

Cheers,
Longman