double fault -> PAGE_KERNEL flagged memory

[Tom Zanussi]

Mathieu Desnoyers writes:
 > * Tom Zanussi (zanussi@us.ibm.com) wrote:
 > > It already is PAGE_KERNEL. 
 > 
 > You are right.
 > 
 > > The page faults you see with relayfs are
 > > vmalloc page faults i.e. minor faults that just update the kernel part
 > > of the current process's page table with the buffer pages.
 > > 
 > 
 > Generally speaking, what would happen if :
 > 
 > - A page fault handler has a trace point that logs an event in the RelayFS
 >   buffer.
 > - This exact write causes a (minor) page fault.
 > 
 > It may not happen often, but I think it would lead to a double fault. Is this
 > case possible ?
 > 

Yes, I'm sure it is possible, in fact I'm sure it happens all the time
in LTT and it's never been a problem.  Have you verified that it is a
problem (e.g. tracing only page faults and seeing a double fault).

Tom