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