On Fri, Feb 01, 2019 at 04:12:46PM +0800, fei phung wrote: > > I am not sure what does assignment of pointers mean in this context. > > ptr_ring is designed for a single producer and a single consumer. For > > why it works see explanation about data dependencies in > > Documentation/memory-barriers.txt. You will have to be more specific > > about the data race that you see if you expect more specific answers. > > Hi, > > ptr_ring_produce_any(sc->recv[chnl]->msgs, > &item_recv_push[item_recv_push_index]) needs to have > non-NULL pointer assigned for item_recv_push[item_recv_push_index] , right ?
No that's irrelevant. If your item_recv_push_index isn't getting out of bounds then &item_recv_push[item_recv_push_index] won't be NULL and that's all ptr_ring cares about. > Note: > ptr_ring_produce_any() occurs in interrupt handler, while > ptr_ring_consume_any() occurs in thread. > > https://gist.github.com/promach/7716ee8addcaa33fda140d74d1ad94d6/cdc6599b8313e265bdfb073a65a124e1ba3303a2#file-riffa_driver_ptr_ring-c-L306-L320 > > // TX (PC receive) scatter gather buffer is read. > if (vect & (1<<((5*i)+1))) { > recv = 1; > > item_recv_push[item_recv_push_index].val1 = EVENT_SG_BUF_READ; > item_recv_push[item_recv_push_index].val2 = 0; > > // Keep track so the thread can handle this. > if (ptr_ring_produce_any(sc->recv[chnl]->msgs, > &item_recv_push[item_recv_push_index])) { > printk(KERN_ERR "riffa: fpga:%d chnl:%d, recv sg buf > read msg queue full\n", sc->id, chnl); > } > DEBUG_MSG(KERN_INFO "riffa: fpga:%d chnl:%d, recv sg buf > read\n", sc->id, chnl); > > item_recv_push_index++; > } > > > The kernel log points me to ptr_ring_consume_any(). So, this is > definitely data race issue > with my own ptr_ring interfacing code. > > besides, I am also getting a reference to zero-length ring for the > kernel dmesg log. > I am not sure how this is related to the data race though. > > The kernel log points to > https://github.com/torvalds/linux/blame/master/include/linux/ptr_ring.h#L175 > (click open git blame on this line) > > Regards, > Phung Sorry I'm not sure what you are trying to say here. If I had to guess I'd say the way you play with indices is probably racy so you are producing an invalid index. -- MST
