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>Common Techniques</H1
><P
> This section lists some common dilemmas and the standard
solutions used in the Linux kernel code. If you use these,
people will find your code simpler to understand.
</P
><P
> If I could give you one piece of advice: never sleep with anyone
crazier than yourself. But if I had to give you advice on
locking: <I
CLASS="EMPHASIS"
>keep it simple</I
>.
</P
><P
> Lock data, not code.
</P
><P
> Be reluctant to introduce new locks.
</P
><P
> Strangely enough, this is the exact reverse of my advice when
you <I
CLASS="EMPHASIS"
>have</I
> slept with someone crazier than yourself.
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>No Writers in Interrupt Context</H1
><P
> There is a fairly common case where an interrupt handler needs
access to a critical region, but does not need write access.
In this case, you do not need to use
<TT
CLASS="FUNCTION"
>read_lock_irq()</TT
>, but only
<TT
CLASS="FUNCTION"
>read_lock()</TT
> everywhere (since if an interrupt
occurs, the irq handler will only try to grab a read lock, which
won't deadlock). You will still need to use
<TT
CLASS="FUNCTION"
>write_lock_irq()</TT
>.
</P
><P
> Similar logic applies to locking between softirqs/tasklets/BHs
which never need a write lock, and user context:
<TT
CLASS="FUNCTION"
>read_lock()</TT
> and
<TT
CLASS="FUNCTION"
>write_lock_bh()</TT
>.
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