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    SubjectRe: [PATCH V3 2/7] dmaengine/dw_dmac: Replace spin_lock* with irqsave variants
    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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