Eugene Shatokhin <eugene.shatokhin@xxxxxxxxxx> writes: > The problem is not in the reordering but rather in the fact that > "dev->flags = 0" is not necessarily atomic > w.r.t. "clear_bit(EVENT_RX_KILL, &dev->flags)", and vice versa. > > So the following might be possible, although unlikely: > > CPU0 CPU1 > clear_bit: read dev->flags > clear_bit: clear EVENT_RX_KILL in the read value > > dev->flags=0; > > clear_bit: write updated dev->flags > > As a result, dev->flags may become non-zero again. Ah, right. Thanks for explaining. > I cannot prove yet that this is an impossible situation. If anyone > can, please explain. If so, this part of the patch will not be needed. I wonder if we could simply move the dev->flags = 0 down a few lines to fix both issues? It doesn't seem to do anything useful except for resetting the flags to a sane initial state after the device is down. Stopping the tasklet rescheduling etc depends only on netif_running(), which will be false when usbnet_stop is called. There is no need to touch dev->flags for this to happen. >> The EVENT_NO_RUNTIME_PM bug should definitely be fixed. Please split >> that out as a separate fix. It's a separate issue, and should be >> backported to all maintained stable releases it applies to (anything >> from v3.8 and newer) > > Yes, that makes sense. However, this fix was originally provided by > Oliver Neukum rather than me, so I would like to hear his opinion as > well first. If what I write above is correct (please help me verify...), then maybe it does make sense to do these together anyway. Bjørn -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
