Messages in this thread | | | Date | Thu, 28 Apr 2011 18:10:20 +0100 | From | Russell King - ARM Linux <> | Subject | Re: [PATCH V3 2/7] dmaengine/dw_dmac: Replace spin_lock* with irqsave variants |
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On Wed, Apr 27, 2011 at 03:06:44PM +0530, Viresh Kumar wrote: > @@ -407,6 +410,8 @@ EXPORT_SYMBOL(dw_dma_get_dst_addr); > static void dwc_handle_cyclic(struct dw_dma *dw, struct dw_dma_chan *dwc, > u32 status_block, u32 status_err, u32 status_xfer) > { > + unsigned long flags; > + > if (status_block & dwc->mask) { > void (*callback)(void *param); > void *callback_param; > @@ -418,9 +423,9 @@ static void dwc_handle_cyclic(struct dw_dma *dw, struct dw_dma_chan *dwc, > callback = dwc->cdesc->period_callback; > callback_param = dwc->cdesc->period_callback_param; > if (callback) { > - spin_unlock(&dwc->lock); > + spin_unlock_irqrestore(&dwc->lock, flags); > callback(callback_param); > - spin_lock(&dwc->lock); > + spin_lock_irqsave(&dwc->lock, flags);
I'm really not convinced that this is anywhere near correct. I'm surprised this doesn't spit out a compiler warning.
spin_unlock_irqrestore() reads the flags argument and puts it into the PSR. spin_lock_irqsave() reads the PSR, puts it into the flags argument, sets the interrupt mask bit and writes back to the PSR.
So, if you do:
unsigned long flags;
spin_unlock_irqrestore(&dwc->lock, flags); ... spin_lock_irqsave(&dwc->lock, flags);
you're going to end up corrupting the PSR.
In any case, releasing a spinlock temporarily within a called function is _really_ not a nice thing to do. It makes code review rather difficult as called functions become non-atomic when called within an atomic region.
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