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>Locking Between User Context and BHs</H1
><P
> If a <A
HREF="g388.html#GLOSS-BH"
><I
CLASS="FIRSTTERM"
>bottom half</I
></A
> shares
data with user context, you have two problems. Firstly, the current
user context can be interrupted by a bottom half, and secondly, the
critical region could be entered from another CPU. This is where
<TT
CLASS="FUNCTION"
>spin_lock_bh()</TT
>
(<TT
CLASS="FILENAME"
>include/linux/spinlock.h</TT
>) is
used. It disables bottom halves on that CPU, then grabs the lock.
<TT
CLASS="FUNCTION"
>spin_unlock_bh()</TT
> does the reverse.
</P
><P
> This works perfectly for <A
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> as well: the spin lock vanishes, and this macro
simply becomes <TT
CLASS="FUNCTION"
>local_bh_disable()</TT
>
(<TT
CLASS="FILENAME"
>include/asm/softirq.h</TT
>), which
protects you from the bottom half being run.
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