Lino Sanfilippo <LinoSanfilippo at gmx.de> : [...] > I dont agree here. A dma_wmb would have an effect to "data" and "info", yes, > but it would have absolutely no effect to skb_tx_timestamp(), since there > is no dma access involved here. In fact skb_tx_timestamp() could probably > be even reordered to appear after the dma_wmb. > > Anyway, there is the wmb() directly after the assignment to "info". _This_ > barrier should ensure that skb_tx_timestamp() (along with a flush of data > and info to DMA) is executed before "txbd_curr" is advanced. > This means that the corresponding skb cant be freed prematurely by tx_clean(). The concern here is about sending adequate PTP payload on the network. skb_tx_timestamp() is used for network clock synchronization. Some extra information must be transmitted. Be it through direct payload change or through indirect control, it _is_ related to dma. Several (most ?) skb_tx_timestamp() misuses blur the picture: CPU vs device sync is of course way below the radar when the driver crashes because of plain use-after-free skb_tx_timestamp() :o/ -- Ueimor
