[PATCH -tip] locking/mutex: Complain upon api misuse wrt interrupt context

[PATCH -tip] locking/mutex: Complain upon api misuse wrt interrupt context

[Davidlohr Bueso]

Sprinkle warning checks, under CONFIG_DEBUG_MUTEXES. While the mutex
rules and semantics are explicitly documented, this allows to expose
any abusers and robustifies the whole thing. While trylock and unlock
are non-blocking, calling from irq context is still forbidden (lock
must be within the same context as unlock).

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
 kernel/locking/mutex.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 468a9b8422e3..7e9c316c646c 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -733,6 +733,9 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
  */
 void __sched mutex_unlock(struct mutex *lock)
 {
+#ifdef CONFIG_DEBUG_MUTEXES
+	WARN_ON(in_interrupt());
+#endif
 #ifndef CONFIG_DEBUG_LOCK_ALLOC
 	if (__mutex_unlock_fast(lock))
 		return;
@@ -1413,6 +1416,7 @@ int __sched mutex_trylock(struct mutex *lock)
 
 #ifdef CONFIG_DEBUG_MUTEXES
 	DEBUG_LOCKS_WARN_ON(lock->magic != lock);
+	WARN_ON(in_interrupt());
 #endif
 
 	locked = __mutex_trylock(lock);
-- 
2.16.4

Re: [PATCH -tip] locking/mutex: Complain upon api misuse wrt interrupt context

[Peter Zijlstra]

On Thu, Oct 24, 2019 at 08:36:34PM -0700, Davidlohr Bueso wrote:
> Sprinkle warning checks, under CONFIG_DEBUG_MUTEXES. While the mutex
> rules and semantics are explicitly documented, this allows to expose
> any abusers and robustifies the whole thing. While trylock and unlock
> are non-blocking, calling from irq context is still forbidden (lock
> must be within the same context as unlock).
> 
> Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
> ---
>  kernel/locking/mutex.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
> index 468a9b8422e3..7e9c316c646c 100644
> --- a/kernel/locking/mutex.c
> +++ b/kernel/locking/mutex.c
> @@ -733,6 +733,9 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
>   */
>  void __sched mutex_unlock(struct mutex *lock)
>  {
> +#ifdef CONFIG_DEBUG_MUTEXES
> +	WARN_ON(in_interrupt());
> +#endif
>  #ifndef CONFIG_DEBUG_LOCK_ALLOC
>  	if (__mutex_unlock_fast(lock))
>  		return;
> @@ -1413,6 +1416,7 @@ int __sched mutex_trylock(struct mutex *lock)
>  
>  #ifdef CONFIG_DEBUG_MUTEXES
>  	DEBUG_LOCKS_WARN_ON(lock->magic != lock);
> +	WARN_ON(in_interrupt());
>  #endif
>  
>  	locked = __mutex_trylock(lock);


No real objection, but should not lockdep already complain about this?
__mutex_unlock_slowpath() takes ->wait_lock irq-unsafe, so then using it
from an IRQ should generate an insta IRQ inversion report.

Re: [PATCH -tip] locking/mutex: Complain upon api misuse wrt interrupt context

[Davidlohr Bueso]

On Fri, 25 Oct 2019, Peter Zijlstra wrote:
>No real objection, but should not lockdep already complain about this?
>__mutex_unlock_slowpath() takes ->wait_lock irq-unsafe, so then using it
>from an IRQ should generate an insta IRQ inversion report.

But we still have the unlock fastpath and the trylock scenarios which
don't take locks.

Thanks,
davidlohr

[tip: locking/core] locking/mutex: Complain upon mutex API misuse in IRQ contexts

[tip-bot2 for Davidlohr Bueso]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     a0855d24fc22d49cdc25664fb224caee16998683
Gitweb:        https://git.kernel.org/tip/a0855d24fc22d49cdc25664fb224caee16998683
Author:        Davidlohr Bueso <dave@stgolabs.net>
AuthorDate:    Thu, 24 Oct 2019 20:36:34 -07:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 29 Oct 2019 12:22:52 +01:00

locking/mutex: Complain upon mutex API misuse in IRQ contexts

Add warning checks if mutex_trylock() or mutex_unlock() are used in
IRQ contexts, under CONFIG_DEBUG_MUTEXES=y.

While the mutex rules and semantics are explicitly documented, this allows
to expose any abusers and robustifies the whole thing.

While trylock and unlock are non-blocking, calling from IRQ context
is still forbidden (lock must be within the same context as unlock).

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dave@stgolabs.net
Link: https://lkml.kernel.org/r/20191025033634.3330-1-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/locking/mutex.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 5352ce5..54cc5f9 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -733,6 +733,9 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
  */
 void __sched mutex_unlock(struct mutex *lock)
 {
+#ifdef CONFIG_DEBUG_MUTEXES
+	WARN_ON(in_interrupt());
+#endif
 #ifndef CONFIG_DEBUG_LOCK_ALLOC
 	if (__mutex_unlock_fast(lock))
 		return;
@@ -1413,6 +1416,7 @@ int __sched mutex_trylock(struct mutex *lock)
 
 #ifdef CONFIG_DEBUG_MUTEXES
 	DEBUG_LOCKS_WARN_ON(lock->magic != lock);
+	WARN_ON(in_interrupt());
 #endif
 
 	locked = __mutex_trylock(lock);