In the following openSUSE bug report https://bugzilla.suse.com/show_bug.cgi?id=1075876 Achim reported an oops related to e1000e timestamping: kernel: RIP: 0010:[<ffffffff8110303f>] timecounter_read+0xf/0x50 [...] kernel: Call Trace: kernel: [<ffffffffa0806b0f>] e1000e_phc_gettime+0x2f/0x60 [e1000e] kernel: [<ffffffffa0806c5d>] e1000e_systim_overflow_work+0x1d/0x80 [e1000e] kernel: [<ffffffff810992c5>] process_one_work+0x155/0x440 kernel: [<ffffffff81099e16>] worker_thread+0x116/0x4b0 kernel: [<ffffffff8109f422>] kthread+0xd2/0xf0 kernel: [<ffffffff8163184f>] ret_from_fork+0x3f/0x70
It always occurs 4 hours after boot but not on every boot. It is most likely the same problem reported here: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1668356 http://lkml.iu.edu/hypermail/linux/kernel/1506.2/index.html#02530 https://bugzilla.redhat.com/show_bug.cgi?id=1463882 https://bugzilla.redhat.com/show_bug.cgi?id=1431863 This occurs with MAC: 12, e1000_pch_spt/I219. The reporter has reproduced it on a v4.16 derivative. We've traced it to the fact that e1000e_systim_reset() skips the timecounter_init() call if e1000e_get_base_timinca() returns -EINVAL, which leads to a null deref in timecounter_read() (see comment 8 of the suse bugzilla for more details.) In commit 83129b37ef35 ("e1000e: fix systim issues", v4.2-rc1) Yanir reworked e1000e_get_base_timinca() in such a way that it can return -EINVAL for e1000_pch_spt if the SYSCFI bit is not set in TSYNCRXCTL. This is also the commit that was identified by bisection in the second link above (lkml). What we've observed (in comment 14) is that TSYNCRXCTL reads sometimes don't have the SYSCFI bit set. Retrying the read shortly after finds the bit to be set. This was observed at boot (probe) but also link up and link down. I have a few questions: What's the purpose of the SYSCFI bit in TSYNCRXCTL ("Reserved" in the datasheet)? Why does it look like subsequent reads of TSYNCRXCTL sometimes have the SYSCFI bit set/not set on I219? Is it right to check the SYSCFI bit in e1000e_get_base_timinca() for _spt and return -EINVAL if it's not set? Could we just remove that check? The patch in comment 13 of the suse bugzilla works around the problem by retrying TSYNCRXCTL reads, maybe we could instead remove that read altogether or move the timecounter_init() call to at least avoid the oops. The best approach to take seems to depend on the behavior expected of TSYNCRXCTL reads on I219 so I'm hoping that you could provide more info on that. Thanks, -Benjamin
