locking/mutex: Improve documentation

On Wed, Mar 14, 2018 at 01:56:31PM -0700, Andrew Morton wrote:

> My memory is weak and our documentation is awful.  What does
> mutex_lock_killable() actually do and how does it differ from
> mutex_lock_interruptible()?

Add kernel-doc for mutex_lock_killable() and mutex_lock_io().  Reword the
kernel-doc for mutex_lock_interruptible().

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: cl@linux.com
Cc: tj@kernel.org
Link: http://lkml.kernel.org/r/20180315115812.GA9949@bombadil.infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/locking/mutex.c

@@ -1082,15 +1082,16 @@ static noinline int __sched
 __mutex_lock_interruptible_slowpath(struct mutex *lock);
 
 /**
- * mutex_lock_interruptible - acquire the mutex, interruptible
- * @lock: the mutex to be acquired
+ * mutex_lock_interruptible() - Acquire the mutex, interruptible by signals.
+ * @lock: The mutex to be acquired.
  *
- * Lock the mutex like mutex_lock(), and return 0 if the mutex has
- * been acquired or sleep until the mutex becomes available. If a
- * signal arrives while waiting for the lock then this function
- * returns -EINTR.
+ * Lock the mutex like mutex_lock().  If a signal is delivered while the
+ * process is sleeping, this function will return without acquiring the
+ * mutex.
  *
- * This function is similar to (but not equivalent to) down_interruptible().
+ * Context: Process context.
+ * Return: 0 if the lock was successfully acquired or %-EINTR if a
+ * signal arrived.
  */
 int __sched mutex_lock_interruptible(struct mutex *lock)
 {
@@ -1104,6 +1105,18 @@ int __sched mutex_lock_interruptible(struct mutex *lock)
 
 EXPORT_SYMBOL(mutex_lock_interruptible);
 
+/**
+ * mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
+ * @lock: The mutex to be acquired.
+ *
+ * Lock the mutex like mutex_lock().  If a signal which will be fatal to
+ * the current process is delivered while the process is sleeping, this
+ * function will return without acquiring the mutex.
+ *
+ * Context: Process context.
+ * Return: 0 if the lock was successfully acquired or %-EINTR if a
+ * fatal signal arrived.
+ */
 int __sched mutex_lock_killable(struct mutex *lock)
 {
 	might_sleep();
@@ -1115,6 +1128,16 @@ int __sched mutex_lock_killable(struct mutex *lock)
 }
 EXPORT_SYMBOL(mutex_lock_killable);
 
+/**
+ * mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O
+ * @lock: The mutex to be acquired.
+ *
+ * Lock the mutex like mutex_lock().  While the task is waiting for this
+ * mutex, it will be accounted as being in the IO wait state by the
+ * scheduler.
+ *
+ * Context: Process context.
+ */
 void __sched mutex_lock_io(struct mutex *lock)
 {
 	int token;