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SubjectRe: spinlock help
hi

spin_lock_irq() and spin_lock_bh()

can they be of any use to u?

"Hen, Shmulik" wrote:
>
> How about if the same sequence occurred, but from two different drivers ?
>
> We've had some bad experience with this stuff. Our driver, which acts as an
> intermediate net driver, would call the hard_start_xmit in the base driver.
> The base driver, wanting to block receive interrupts would issue a
> 'spin_lock_irqsave(a,b)' and process the packet. If the TX queue is full, it
> could call an indication entry point in our intermediate driver to signal it
> to stop sending more packets. Since our indication function handles many
> types of indications but can process them only one at a time, we wanted to
> block other indications while queuing the request.
>
> The whole sequence would look like that:
>
> [our driver]
> ans_send() {
> .
> .
> e100_hard_start_xmit(dev, skb);
> .
> .
> }
>
> [e100.o]
> e100_hard_start_xmit() {
> .
> .
> spin_lock_irqsave(a,b);
> .
> .
> if(tx_queue_full)
> ans_notify(TX_QUEUE_FULL); <--
> .
> .
> spin_unlock_irqrestore(a,b);
> }
>
> [our driver]
> ans_notify() {
> .
> .
> spin_lock_irqsave(c,d);
> queue_request(req_type);
> spin_unlock_irqrestore(c,d); <--
> .
> .
> }
>
> At that point, for some reason, interrupts were back and the e100.o would
> hang in an infinite loop (we verified it on kernel 2.4.0-test10 +kdb that
> the processor was enabling interrupts and that the e100_isr was called for
> processing an Rx int.).
>
> How is that possible that a 'spin_unlock_irqrestore(c,d)' would also restore
> what should have been restored only with a 'spin_unlock_irqrestore(a,b)' ?
>
> Thanks in advance,
> Shmulik Hen
> Software Engineer
> Linux Advanced Networking Services
> Intel Network Communications Group
> Jerusalem, Israel.
>
> -----Original Message-----
> From: Nigel Gamble [mailto:nigel@nrg.org]
> Sent: Wednesday, March 07, 2001 1:54 AM
> To: Manoj Sontakke
> Cc: linux-kernel@vger.kernel.org
> Subject: Re: spinlock help
>
> On Tue, 6 Mar 2001, Manoj Sontakke wrote:
> > 1. when spin_lock_irqsave() function is called the subsequent code is
> > executed untill spin_unloc_irqrestore()is called. is this right?
>
> Yes. The protected code will not be interrupted, or simultaneously
> executed by another CPU.
>
> > 2. is this sequence valid?
> > spin_lock_irqsave(a,b);
> > spin_lock_irqsave(c,d);
>
> Yes, as long as it is followed by:
>
> spin_unlock_irqrestore(c, d);
> spin_unlock_irqrestore(a, b);
>
> Nigel Gamble nigel@nrg.org
> Mountain View, CA, USA. http://www.nrg.org/
>
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--
Regards,
Manoj Sontakke
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