On 9/3/21 8:24 AM, Xiaoguang Wang wrote: > IIUC, IORING_POLL_ADD_MULTI is similar to epoll's edge-triggered mode, > that means once one pure poll request returns one event(cqe), we'll > need to read or write continually until EAGAIN is returned, then I think > there is a possible poll event lost race in multi shot mode: > > t1 poll request add | | > t2 | | > t3 event happens | | > t4 task work add | | > t5 | task work run | > t6 | commit one cqe | > t7 | | user app handles cqe > t8 | new event happen | > t9 | add back to waitqueue | > t10 | > > After t6 but before t9, if new event happens, there'll be no wakeup > operation, and if user app has picked up this cqe in t7, read or write > until EAGAIN is returned. In t8, new event happens and will be lost, > though this race window maybe small. > > To fix this possible race, add poll request back to waitqueue before > committing cqe. Applied, thanks. -- Jens Axboe
