> I could just force all of the seqbegins to hit the slowpath by hacking
Only if you don't believe it will really crash? I think it's pretty
clear even without trying it.
There's no raw_seqlock_t anywhere in mainline?
Anyways the variable is declared (in mainline) in asm-x86/vgtod.h
I guess you could define a new seqlock_t which is explicitely user space
safe. That might avoid such issues in the future. But then
that would likely require some code duplication and be ugly.
On the other hand whatever problem you fixing in the kernel
(to be honest it's still unclear to me what the problem is)
needs to be likely fixed for the userland lock too.