Remove safety belt: it is now ok to do a mtx_trylock() on a mutex you

already own.  The mtx_trylock() will fail however.  Enhance the comment
at the top of the try lock function to explain this.

Requested by:	jlemon and his evil netisr locking

2 files changed, 8 insertions, 10 deletions

diff --git a/sys/kern/kern_mutex.c b/sys/kern/kern_mutex.c
index d2d907f..9f59577 100644
--- a/sys/kern/kern_mutex.c
+++ b/sys/kern/kern_mutex.c
@@ -454,8 +454,10 @@ _mtx_unlock_spin_flags(struct mtx *m, int opts, const char *file, int line)
 
 /*
  * The important part of mtx_trylock{,_flags}()
- * Tries to acquire lock `m.' We do NOT handle recursion here; we assume that
- * if we're called, it's because we know we don't already own this lock.
+ * Tries to acquire lock `m.' We do NOT handle recursion here.  If this
+ * function is called on a recursed mutex, it will return failure and
+ * will not recursively acquire the lock.  You are expected to know what
+ * you are doing.
  */
 int
 _mtx_trylock(struct mtx *m, int opts, const char *file, int line)
@@ -464,9 +466,6 @@ _mtx_trylock(struct mtx *m, int opts, const char *file, int line)
 
 	MPASS(curthread != NULL);
 
-	KASSERT(!mtx_owned(m),
-	    ("mtx_trylock() called on a mutex already owned"));
-
 	rval = _obtain_lock(m, curthread);
 
 	LOCK_LOG_TRY("LOCK", &m->mtx_object, opts, rval, file, line);
diff --git a/sys/kern/subr_turnstile.c b/sys/kern/subr_turnstile.c
index d2d907f..9f59577 100644
--- a/sys/kern/subr_turnstile.c
+++ b/sys/kern/subr_turnstile.c
@@ -454,8 +454,10 @@ _mtx_unlock_spin_flags(struct mtx *m, int opts, const char *file, int line)
 
 /*
  * The important part of mtx_trylock{,_flags}()
- * Tries to acquire lock `m.' We do NOT handle recursion here; we assume that
- * if we're called, it's because we know we don't already own this lock.
+ * Tries to acquire lock `m.' We do NOT handle recursion here.  If this
+ * function is called on a recursed mutex, it will return failure and
+ * will not recursively acquire the lock.  You are expected to know what
+ * you are doing.
  */
 int
 _mtx_trylock(struct mtx *m, int opts, const char *file, int line)
@@ -464,9 +466,6 @@ _mtx_trylock(struct mtx *m, int opts, const char *file, int line)
 
 	MPASS(curthread != NULL);
 
-	KASSERT(!mtx_owned(m),
-	    ("mtx_trylock() called on a mutex already owned"));
-
 	rval = _obtain_lock(m, curthread);
 
 	LOCK_LOG_TRY("LOCK", &m->mtx_object, opts, rval, file, line);