linux-kernel - Re: [PATCH 1/2] security/apparmor: Replace homebrew use of write_can

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Date:   Tue, 3 Oct 2017 17:58:48 +0100
From:   Will Deacon <will.deacon@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, john.johansen@...onical.com,
        paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 1/2] security/apparmor: Replace homebrew use of
 write_can_lock with lockdep

On Tue, Oct 03, 2017 at 05:07:09PM +0200, Peter Zijlstra wrote:
> On Tue, Oct 03, 2017 at 03:32:45PM +0100, Will Deacon wrote:
> > The lockdep subsystem provides a robust way to assert that a lock is
> > held, so use that instead of write_can_lock, which can give incorrect
> > results for qrwlocks.
> > 
> > Cc: John Johansen <john.johansen@...onical.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Signed-off-by: Will Deacon <will.deacon@....com>
> 
> Thanks Will, good to be able to finally remove that API.

Yup, but my grep-fu missed these guys in kernel/locking/spinlock.c:

	while (!raw_##op##_can_lock(lock) && (lock)->break_lock

so diff below to catch those and remove spin_can_lock too.

Let me spin a v2...

Will

--->8

diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 69e079c5ff98..1e3e48041800 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -278,12 +278,6 @@ static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
 	1 : ({ local_irq_restore(flags); 0; }); \
 })
 
-/**
- * raw_spin_can_lock - would raw_spin_trylock() succeed?
- * @lock: the spinlock in question.
- */
-#define raw_spin_can_lock(lock)	(!raw_spin_is_locked(lock))
-
 /* Include rwlock functions */
 #include <linux/rwlock.h>
 
@@ -396,11 +390,6 @@ static __always_inline int spin_is_contended(spinlock_t *lock)
 	return raw_spin_is_contended(&lock->rlock);
 }
 
-static __always_inline int spin_can_lock(spinlock_t *lock)
-{
-	return raw_spin_can_lock(&lock->rlock);
-}
-
 #define assert_spin_locked(lock)	assert_raw_spin_locked(&(lock)->rlock)
 
 /*
diff --git a/kernel/locking/spinlock.c b/kernel/locking/spinlock.c
index 42ee9d0a1ea4..8fd48b5552a7 100644
--- a/kernel/locking/spinlock.c
+++ b/kernel/locking/spinlock.c
@@ -66,7 +66,7 @@ void __lockfunc __raw_##op##_lock(locktype##_t *lock)			\
 									\
 		if (!(lock)->break_lock)				\
 			(lock)->break_lock = 1;				\
-		while (!raw_##op##_can_lock(lock) && (lock)->break_lock)\
+		while ((lock)->break_lock)				\
 			arch_##op##_relax(&lock->raw_lock);		\
 	}								\
 	(lock)->break_lock = 0;						\
@@ -86,7 +86,7 @@ unsigned long __lockfunc __raw_##op##_lock_irqsave(locktype##_t *lock)	\
 									\
 		if (!(lock)->break_lock)				\
 			(lock)->break_lock = 1;				\
-		while (!raw_##op##_can_lock(lock) && (lock)->break_lock)\
+		while ((lock)->break_lock)				\
 			arch_##op##_relax(&lock->raw_lock);		\
 	}								\
 	(lock)->break_lock = 0;						\