Got reviewed by Ethan offline, so pushed to master,
On Tue, Mar 25, 2014 at 3:18 PM, Alex Wang <al...@nicira.com> wrote:
> Hey Ben,
>
> Could you review this?
>
> Thanks,
> Alex Wang,
>
>
> On Tue, Mar 25, 2014 at 2:24 PM, Alex Wang <al...@nicira.com> wrote:
>
>> Commit 61057e884ca9c(ofproto-dpif-upcall: Slightly simplify
>> udpif_upcall_handler().) restructured the main loop in
>> udpif_upcall_handler() and discarded the check for the
>> 'exit_latch' after acquiring the mutex. This makes it
>> possible for the following race:
>>
>> - main thread sets the 'exit_latch' after the handler thread
>> checking it.
>> - main thread acquires the handler thread mutex and signals the
>> condition variable of handler thread.
>> - main thread releases the mutex and 'join' the handler thread.
>> - handler thread acquires the mutex, finds that n_upcalls is 0
>> and waits on the signal of condition variable.
>> - then OVS will hang forever.
>>
>> This commit fixes the above issue by adding a check for the
>> 'exit_latch' after acquiring the mutex.
>>
>> Bug #1217229
>>
>> Signed-off-by: Alex Wang <al...@nicira.com>
>> ---
>> ofproto/ofproto-dpif-upcall.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/ofproto/ofproto-dpif-upcall.c b/ofproto/ofproto-dpif-upcall.c
>> index b931ab6..5b5fb6e 100644
>> --- a/ofproto/ofproto-dpif-upcall.c
>> +++ b/ofproto/ofproto-dpif-upcall.c
>> @@ -695,7 +695,10 @@ udpif_upcall_handler(void *arg)
>> size_t i;
>>
>> ovs_mutex_lock(&handler->mutex);
>> - if (!handler->n_upcalls) {
>> + /* Must check the 'exit_latch' again to make sure the main
>> thread is
>> + * not joining on the handler thread. */
>> + if (!handler->n_upcalls
>> + && !latch_is_set(&handler->udpif->exit_latch)) {
>> ovs_mutex_cond_wait(&handler->wake_cond, &handler->mutex);
>> }
>>
>> --
>> 1.7.9.5
>>
>>
>
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