On Thu, Feb 25, 2010 at 08:34:42AM -0700, Rick L. Vinyard, Jr. wrote: > Jiri Kosina wrote: > > On Wed, 24 Feb 2010, Rick L. Vinyard, Jr. wrote: > > > >> The key difference is the replacement of spin_lock() with spin_trylock() > >> such that if the non-interrupt code has already obtained the lock, the > >> interrupt will not deadlock but instead take the else path and schedule > >> a > >> framebuffer update at the next interval. > > > > Why is _irqsave() and/or deferred work not enough? The aproach with > > _trylock() seems to be overly complicated for no good reason (I personally > > become very suspicious every time I see code that is using _trylock()). > > > > I was concerned about _irqsave() because the lock is split across two > functions to protect the urb after it is handed off to the usb subsystem > with usb_submit_urb(). It's locked in g13_fb_send() and unlocked in the > urb completion callback. > > As for deferred work, the g13_fb_send() is the I/O portion of the deferred > framebuffer callback. I was concerned that without a lock one deferred > update could hand the urb off to the usb subsystem and a second could try > to access it before it was handed back to the driver. > > In this case the _trylock() would fail and in the else patch we would > defer yet again until the next update cycle. > What you are looking for here is called test_and_set_bit(). Do not muddy the waters with a lock. -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
