[PATCH] mutex subsystem, documentation
Add mutex design related documentation.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@infradead.org>
diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl
index 90dc2de..158ffe9 100644
--- a/Documentation/DocBook/kernel-locking.tmpl
+++ b/Documentation/DocBook/kernel-locking.tmpl
@@ -222,7 +222,7 @@
<title>Two Main Types of Kernel Locks: Spinlocks and Semaphores</title>
<para>
- There are two main types of kernel locks. The fundamental type
+ There are three main types of kernel locks. The fundamental type
is the spinlock
(<filename class="headerfile">include/asm/spinlock.h</filename>),
which is a very simple single-holder lock: if you can't get the
@@ -230,16 +230,22 @@
very small and fast, and can be used anywhere.
</para>
<para>
- The second type is a semaphore
+ The second type is a mutex
+ (<filename class="headerfile">include/linux/mutex.h</filename>): it
+ is like a spinlock, but you may block holding a mutex.
+ If you can't lock a mutex, your task will suspend itself, and be woken
+ up when the mutex is released. This means the CPU can do something
+ else while you are waiting. There are many cases when you simply
+ can't sleep (see <xref linkend="sleeping-things"/>), and so have to
+ use a spinlock instead.
+ </para>
+ <para>
+ The third type is a semaphore
(<filename class="headerfile">include/asm/semaphore.h</filename>): it
can have more than one holder at any time (the number decided at
initialization time), although it is most commonly used as a
- single-holder lock (a mutex). If you can't get a semaphore,
- your task will put itself on the queue, and be woken up when the
- semaphore is released. This means the CPU will do something
- else while you are waiting, but there are many cases when you
- simply can't sleep (see <xref linkend="sleeping-things"/>), and so
- have to use a spinlock instead.
+ single-holder lock (a mutex). If you can't get a semaphore, your
+ task will be suspended and later on woken up - just like for mutexes.
</para>
<para>
Neither type of lock is recursive: see