Re: context overflow

tom_gall@vnet.ibm.com wrote:

  current->mm I believe is correct. active_mm for tasks in user space just point
back to mm. kernel space tasks will have an mm of NULL yet their active_mm will
point back to the last user space task they ran.

Not exactly.  Every task running on a CPU must have an active_mm, and
it represents the current context for the MMU.  This active_mm comes
from a single threaded application's 'mm', or in the case of a
thread without an 'mm' from the previous application that ran, or
from somewhere else depending upon VM_CLONE games.

The point you are missing is 'active_mm' represents the current
context for the MMU.  If you get a context overflow, you can't skip
getting and setting a context for an active task just because it
doesn't have a 'current->mm'.  Your modification to do this
results in a task running on a CPU with a "NO CONTEXT" mm, and worse
and incorrect VSID/ASID/PID/whatever for the task running on that MMU.

  The reason for this patch is in the case where the idle task comes in on one
processor and on another processor it has encountered a context overflow.

It's not just the idle task.  It could be any task that is supposed
to get an active_mm from someone else.

The patch is just logically incorrect.  There should be no
'if current->mm' and it should get/set context on current->active_mm.


	-- Dan

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