annotating semaphores.

[Dave Jones]

Today I came across a bug in the kernel cpufreq code where
we were missing a bunch of up_write() calls in error paths
of a function.

I've been trying to get sparse's context checking to pick up
on the errors and failing.  The kernel patch below is what I have
so far, but it seems to report no output whatsoever.
What am I missing ?

        Dave

diff --git a/include/asm-x86/rwsem.h b/include/asm-x86/rwsem.h
index 041906f..3111853 100644
--- a/include/asm-x86/rwsem.h
+++ b/include/asm-x86/rwsem.h
@@ -106,6 +106,7 @@ LOCK_PREFIX "  incl      (%%eax)\n\t" /* adds 0x00000001, 
returns the old value
                : "+m" (sem->count)
                : "a" (sem)
                : "memory", "cc");
+       __acquire(sem);
 }
 
 /*
@@ -128,6 +129,7 @@ LOCK_PREFIX "  cmpxchgl  %2,%0\n\t"
                : "+m" (sem->count), "=&a" (result), "=&r" (tmp)
                : "i" (RWSEM_ACTIVE_READ_BIAS)
                : "memory", "cc");
+       __acquire(sem);
        return result>=0 ? 1 : 0;
 }
 
@@ -167,6 +169,7 @@ static inline int __down_write_trylock(struct rw_semaphore 
*sem)
                                  RWSEM_ACTIVE_WRITE_BIAS);
        if (ret == RWSEM_UNLOCKED_VALUE)
                return 1;
+       __acquire(sem);
        return 0;
 }
 
@@ -186,6 +189,7 @@ LOCK_PREFIX "  xadd      %%edx,(%%eax)\n\t" /* subtracts 1, 
returns the old valu
                : "+m" (sem->count), "=d" (tmp)
                : "a" (sem), "1" (tmp)
                : "memory", "cc");
+       __release(sem);
 }
 
 /*
@@ -204,6 +208,7 @@ LOCK_PREFIX "  xaddl     %%edx,(%%eax)\n\t" /* tries to 
transition 0xffff0001 ->
                : "+m" (sem->count)
                : "a" (sem), "i" (-RWSEM_ACTIVE_WRITE_BIAS)
                : "memory", "cc", "edx");
+       __release(sem);
 }
 
 /*
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index c4e0016..cf110b0 100644
diff --git a/include/linux/rwsem-spinlock.h b/include/linux/rwsem-spinlock.h
index 813cee1..90a4b2b 100644
--- a/include/linux/rwsem-spinlock.h
+++ b/include/linux/rwsem-spinlock.h
@@ -60,13 +60,13 @@ do {                                                        
        \
        __init_rwsem((sem), #sem, &__key);                      \
 } while (0)
 
-extern void FASTCALL(__down_read(struct rw_semaphore *sem));
-extern int FASTCALL(__down_read_trylock(struct rw_semaphore *sem));
-extern void FASTCALL(__down_write(struct rw_semaphore *sem));
+extern void FASTCALL(__down_read(struct rw_semaphore *sem)) __acquires(sem);
+extern int FASTCALL(__down_read_trylock(struct rw_semaphore *sem)) 
__acquires(sem);
+extern void FASTCALL(__down_write(struct rw_semaphore *sem)) __acquires(sem);
 extern void FASTCALL(__down_write_nested(struct rw_semaphore *sem, int 
subclass));
-extern int FASTCALL(__down_write_trylock(struct rw_semaphore *sem));
-extern void FASTCALL(__up_read(struct rw_semaphore *sem));
-extern void FASTCALL(__up_write(struct rw_semaphore *sem));
+extern int FASTCALL(__down_write_trylock(struct rw_semaphore *sem) 
__acquires(sem));
+extern void FASTCALL(__up_read(struct rw_semaphore *sem)) __releases(sem);
+extern void FASTCALL(__up_write(struct rw_semaphore *sem)) __releases(sem);
 extern void FASTCALL(__downgrade_write(struct rw_semaphore *sem));
 
 static inline int rwsem_is_locked(struct rw_semaphore *sem)
diff --git a/lib/rwsem-spinlock.c b/lib/rwsem-spinlock.c
index c4cfd6c..c13d112 100644
--- a/lib/rwsem-spinlock.c
+++ b/lib/rwsem-spinlock.c
@@ -162,6 +162,7 @@ void fastcall __sched __down_read(struct rw_semaphore *sem)
 
        tsk->state = TASK_RUNNING;
  out:
+       __acquire(sem);
        ;
 }
 
@@ -184,6 +185,7 @@ int fastcall __down_read_trylock(struct rw_semaphore *sem)
 
        spin_unlock_irqrestore(&sem->wait_lock, flags);
 
+       __acquire(sem);
        return ret;
 }
 
@@ -228,6 +230,7 @@ void fastcall __sched __down_write_nested(struct 
rw_semaphore *sem, int subclass
 
        tsk->state = TASK_RUNNING;
  out:
+       __acquire(sem);
        ;
 }
 
@@ -253,6 +256,7 @@ int fastcall __down_write_trylock(struct rw_semaphore *sem)
        }
 
        spin_unlock_irqrestore(&sem->wait_lock, flags);
+       __acquire(sem);
 
        return ret;
 }
@@ -270,6 +274,7 @@ void fastcall __up_read(struct rw_semaphore *sem)
                sem = __rwsem_wake_one_writer(sem);
 
        spin_unlock_irqrestore(&sem->wait_lock, flags);
+       __release(sem);
 }
 
 /*
@@ -286,6 +291,7 @@ void fastcall __up_write(struct rw_semaphore *sem)
                sem = __rwsem_do_wake(sem, 1);
 
        spin_unlock_irqrestore(&sem->wait_lock, flags);
+       __release(sem);
 }
 
 /*
-- 
http://www.codemonkey.org.uk
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