On Friday 07 December 2012 00:15:59 Hans J. Koch wrote: > On Thu, Dec 06, 2012 at 11:11:38AM +0200, Vitalii Demianets wrote: > > On Thursday 06 December 2012 04:41:01 Hans J. Koch wrote: > > > > @@ -63,7 +68,7 @@ static irqreturn_t uio_pdrv_genirq_handler(int irq, > > > > struct uio_info *dev_info) > > > > > > * remember the state so we can allow user space to enable it > > > > later. */ > > > > > > > > - if (!test_and_set_bit(0, &priv->flags)) > > > > + if (!test_and_set_bit(UIO_IRQ_DISABLED, &priv->flags)) > > > > disable_irq_nosync(irq); > > > > > > That is not safe. That flag can only be changed by userspace, and if > > > the userspace part is not running, the CPU on which the irq is pending > > > will hang. > > > The handler has to disable the interrupt in any case. > > > (The original version had the same problem, I know...) > > > > Perhaps I'm missing something here, but I don't see your point. If > > userspace is not (implicitly) calling uio_pdrv_genirq_irqcontrol() by > > writing to the device file, then on the first invocation of interrupt > > handler that IRQ is disabled by disable_irq_nosync() and that's the end > > of story - no more irqs, no problems. Until userspace writes non-zero to > > the device file, of course. > > If you run into the irq handler, the interrupt was obviously enabled. Since > irq sharing is not supported by this driver, you ALWAYS have to disable it > because it IS your interrupt. Storing the enabled/disabled status in a > variable is not needed at all here. Or am I missing something? >
Good point. I agree that having UIO_IRQ_DISABLED flag is redundant. Inside the irq handler we know for sure that irq is enabled. In uio_pdrv_genirq_irqcontrol() this knowledge is not mandatory, we could enable/disable irq unconditionally. The only question: I feel uncomfortable mixing in one patch bug fixes (i.e. memory freeing issues) and optimization (removing UIO_IRQ_DISABLED flag). What do you think is the best course of action: a) respin the current patch to the v3 with removing UIO_IRQ_DISABLED flag; or b) do the removing of the flag in a separate patch, dependent on the "Fix memory freeing issues"? > > > > priv->uioinfo = uioinfo; > > > > spin_lock_init(&priv->lock); > > > > - priv->flags = 0; /* interrupt is enabled to begin with */ > > > > + /* interrupt is enabled to begin with */ > > > > + priv->flags = uioinfo_alloced ? (1 << UIO_INFO_ALLOCED) : 0; > > > > > > The comment doesn't describe the line it's supposed to comment. > > > > The comment draws attention to the fact that UIO_IRQ_DISABLED is not set > > initially, and this is done on purpose. > > And that's right because the interrupt is initially enabled by > uio_register_device(). > > > Particularly it is done because of > > the potential problem you noted earlier - if userspace is never setting > > this flag, the interrupt handler will disable irq on the first invocation > > thanks to the absence of the flag > > (if(!test_and_set_bit(UIO_IRQ_DISABLED,...) will succeed). > > So, I think we really need some comment explaining how the things are > > arranged here; after all even you haven't got the whole picture on the > > first glance. Maybe the current wording of the comment is not the best. > > I've just left what was there before. > > OK, but we humans tend to read a text from top to bottom, so a comment > should describe the code immediately following it. And that is a line that > deals with memory allocation, not with interrupts. > That line deals with initialization of flags. The comment draws attention to the fact that UIO_IRQ_DISABLED flag is initialized to zero. Anyways, if we agreed on the removing of that flag altogether, this would be no issue and the comment would be simply removed. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
