On Mon, 05 Feb 2007 02:42:09 +0100 Tilman Schmidt [off-list ref] wrote:

Am 04.02.2007 02:56 schrieb Andrew Morton:

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On Sun, 04 Feb 2007 02:32:41 +0100 Tilman Schmidt [off-list ref] wrote:

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+	spin_lock_irqsave(&cs->cmdlock, flags);
+	cb = cs->cmdbuf;
+	spin_unlock_irqrestore(&cs->cmdlock, flags);

It is doubtful if the locking here does anything useful.

It assures atomicity when reading the cs->cmdbuf pointer.

I think it's bogus.  If the quantity being copied here is more than 32-bits
then yes, a lock is appropriate.  But if it's a single word then it's
unlikely that the locking does anything useful.  Or there might be a bug
here.

It's a pointer. Are reads and writes of pointer sized objects
guaranteed to be atomic on every platform?

Yup - we make the same assumption about longs in various places.

It's a bit strange to read a pointer which can be changing at the
same time.  Because the local copy will no longer represent the
thing which it was just copied from.