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Diffstat (limited to 'Documentation/DocBook')
| -rw-r--r-- | Documentation/DocBook/kernel-locking.tmpl | 22 |
1 files changed, 14 insertions, 8 deletions
diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl index 90dc2de8e0af..158ffe9bfade 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 |