Incorrect comment in leave_mm()?

[Keir Fraser]

Hi,

I have a question regarding the per-cpu tlbstate logic that is used to
lazily switch to the swapper_pgdir when running a process with no
mm_struct of its own.

There is a comment in arch/i386/kernel/smp.c:leave_mm() that
states 'We need to reload %cr3 since the page tables may be going away
from under us'. AFAICT this is not true -- the currently-running task
holds a reference on the active_mm until it is context-switched off
the CPU, at which point the reference is dropped in
sched.c:finish_task_switch(). Until that point the pgd cannot be
freed and so kernel mappings should remain valid to use. 

Although the corresponding function in arch/x86_64 doesn't include
this comment, Andi Kleen recently modified it to switch to the
swapper_pg_dir, instead of doing a simple __flush_tlb. Does this mean 
that I am missing something, and the comment in arch/i386 is in fact
correct? 

 Thanks,
 Keir
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