Hi! I've started to wonder why is ping eating 100% CPU shortly after I've upgraded my machine to 4.10 and here is what I found:
The ping main_loop() sleeps in poll() on its socket, the poll() usually times out, at least that's what strace suggets which causes ping to sleep for ~1s in the kernel. See ping source at: https://github.com/iputils/iputils/blob/master/ping_common.c#L587 The poll() seems to start returning POLLERR immediatelly after poll() is called on the socket in a case that connection has dropped for a short while. It seems to be easily reproducible with: * Starting ping with some ip address i.e. ping 4.2.2.2 * Letting it ping for a minute or so * Disconnection a WAN cable from your AP * After a minute or so ping ends up bussy looping on poll() that returns with POLLERR immediatelly * After plugging the cable back the problem gets only worse since we now spend 99% of the time bussy looping on the poll() syscall * And my CPU fan starts to scream loudly I've bisected the problem to this commit: commit f5f99309fa7481f59a500f0d08f3379cd6424c1f (HEAD, refs/bisect/bad) Author: Soheil Hassas Yeganeh <soh...@google.com> Date: Thu Nov 3 18:24:27 2016 -0400 sock: do not set sk_err in sock_dequeue_err_skb -- Cyril Hrubis chru...@suse.cz
