On Wed, 2013-10-09 at 17:01 +0200, Hans de Goede wrote: > usb_wait_anchor_empty_timeout() should wait till the completion handler > has run. Both the zd1211rw driver and the uas driver (in its task mgmt) depend > on the completion handler having completed when > usb_wait_anchor_empty_timeout() > returns, as they read state set by the completion handler after an > usb_wait_anchor_empty_timeout() call. > > But __usb_hcd_giveback_urb() calls usb_unanchor_urb before calling the > completion handler. This is necessary as the completion handler may > re-submit and re-anchor the urb. But this introduces a race where the state > these drivers want to read has not been set yet by the completion handler > (this race is easily triggered with the uas task mgmt code). > > I've considered adding an anchor_count to struct urb, which would be > incremented on anchor and decremented on unanchor, and then only actually > do the anchor / unanchor on 0 -> 1 and 1 -> 0 transtions, combined with > moving the unanchor call in hcd_giveback_urb to after calling the completion > handler. But this will only work if urb's are only re-anchored to the same > anchor as they were anchored to before the completion handler ran. > > And at least one driver re-anchors to another anchor from the completion > handler (rtlwifi). > > So I have come up with this patch instead, which adds the ability to > suspend wakeups of usb_wait_anchor_empty_timeout() waiters to the usb_anchor > functionality, and uses this in __usb_hcd_giveback_urb() to delay wake-ups > until the completion handler has run. > > Signed-off-by: Hans de Goede <hdego...@redhat.com> Acked-by: Oliver Neukum <oli...@neukum.org>
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