Thankfully the Slackware BDFL is not a card-carrying member of the kernel-of-the-week club. Outside the testing branch (Current), not every potential corner case and obtuse kernel vulnerability is patched in the Slackware kernel.
Yet kernel updates do happen. As was the case recently with the Stack Clash bugs.
After updating the kernel to 4.4.74 and then a few days later to 4.4.75, I noticed two of my systems would stall on reboot or halt, at the point when syncing the system clock to the hardware clock.
A 10 second delay.
The two affected systems are AMD systems.
I temporarily modified the
rc.6 script to use the
--directisa parameter. The 10 second timeout disappeared.
Eventually I traced the problem to git commit f0414c1f8bb7a4e69064296f460773170c5435ac. I recompiled the 4.4.75 kernel and reversed the patch. No 10 second timeout.
Although advised not to use the
--directisa parameter, I am doing so anyway. I do not care to maintain my own kernel and I know of no other remedy. I am not noticing any consequences from using the parameter.
In the long run, I was contacted by a kernel developer and asked to test a patch. The patch is supposed to be backported to the 4.4 kernel.