2016-06-15 08:37, Ananyev, Konstantin: > From: Thomas Monjalon [mailto:thomas.monjalon at 6wind.com] > > 2016-06-15 05:30, Pattan, Reshma: > > > From: Thomas Monjalon [mailto:thomas.monjalon at 6wind.com] > > > > 2016-06-14 10:38, Reshma Pattan: > > > > > Added spinlocks around add/remove logic of Rx and Tx callbacks to > > > > > avoid corruption of callback lists in multithreaded context. > > > > > > > > > > Signed-off-by: Reshma Pattan <reshma.pattan at intel.com> > > > > > > > > Why cb->next is not locked in burst functions? > > > It is safe to do "read access" here and doesn't require any locking as > > > rx/tx burst is initiated by only local user(control plane) thread. > > > > > > > Just protecting add/remove but not its usage seems useless. > > > Here locks were required around add/remove to protect "write access" > > > because write to callback list is now done from 2 threads > > > i.e. one from local user thread(control plane) and another from pdump > > > control thread(initiated by remote pdump request). > > > > So read and write can be done by different threads. > > Yes, and this is possible even in current DPDK version (16.04). > What is added by Reshma's patch - now it is possible to have concurrent write > from 2 different thread to that list. > > > I think the read access would need locking but we do not want it > > in fast path. > > I don't think it would be needed. > As I said - read/write interaction didn't change from what we have right now. > But if you have some particular scenario in mind that you believe would cause > a race condition - please speak up.
If we add/remove a callback during a burst? Is it possible that the next pointer would have a wrong value leading to a crash? Maybe we need a comment to state that we should not alter burst callbacks while running burst functions.