Messages in this thread | | | Date | Tue, 16 Dec 2014 08:00:42 -0500 | Subject | Re: [Linaro-acpi] [PATCH] Mailbox: Complete wait event only if Tx was successful | From | Ashwin Chaugule <> |
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On 16 December 2014 at 06:36, Sudeep Holla <sudeep.holla@arm.com> wrote: > On Fri, Dec 12, 2014 at 05:47:26PM +0000, Ashwin Chaugule wrote: >> On 12 December 2014 at 03:43, Sudeep Holla <sudeep.holla@arm.com> wrote: >> > On Thursday 11 December 2014 01:46 AM, Ashwin Chaugule wrote: >> >> >> >> If a wait_for_completion_timeout() call returns due to a timeout, >> >> the mbox code can still call complete() after returning from the wait. >> >> This can cause subsequent transmissions on a channel to fail, since >> >> the wait_for_completion_timeout() sees the completion variable >> >> is !=0, caused by the erroneous complete() call, and immediately >> >> returns without waiting for the time as expected by the client. >> >> >> >> Fix this by calling complete() only if the TX was successful. >> >> >> >> Signed-off-by: Ashwin Chaugule <ashwin.chaugule@linaro.org> >> >> --- >> >> drivers/mailbox/mailbox.c | 2 +- >> >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> >> >> diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c >> >> index 17e9e4a..4acaddb 100644 >> >> --- a/drivers/mailbox/mailbox.c >> >> +++ b/drivers/mailbox/mailbox.c >> >> @@ -101,7 +101,7 @@ static void tx_tick(struct mbox_chan *chan, int r) >> >> if (mssg && chan->cl->tx_done) >> >> chan->cl->tx_done(chan->cl, mssg, r); >> >> >> >> - if (chan->cl->tx_block) >> >> + if ((!r) && chan->cl->tx_block) >> >> complete(&chan->tx_complete); >> > >> > >> > Just curious to check if there's another possible race which is >> > a different issue. >> > >> > Suppose the timer fired and indicated that the Tx is complete, then >> > it tries to execute complete while the wait_for_completion_timeout timed >> > out. Does that make sense ? >> > >> > So if yes, how about adding !completion_done(..) to the check while you >> > are at this ? >> >> Yea. Seems like another race condition. I'll add it along with this.. >> > > Thanks !
IIUC, it looks like adding the !completion_done() will not really fix this race. Once the lock inside wait_for_completion.. is released, completion_done() will return 0, and we'll call complete(), which is not what we want, since the "wait" is already over (after a timeout). I think the only right thing here is to increase the timeout in wait_for_completion_timeout(). Thoughts?
Cheers, Ashwin
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