lowlatency patch question

[<shai@ftcon.com>]

Hi,

I think the following is a bug that can affect kernels patched with
lowlatency, such as Audio… and RedHat AS2.1.

lowlatency patch added conditional_schedule() to be called from
close_files(…) at kernel/exit.c, which seems to raise a problem if the
process had LDT entries.
If it had LDT, at the stage of close_files(…) the tsk->mm already zeroed
(__exit_mm(…), which comes before __exit_files(…) in do_exit(…)).  If
conditional_schedule() at close_files(…) will succeed, switching back into
this process (that now have zeroed tsk->mm) will fail since the kernel will
not use the right LDT (since tsk->mm was zeroed, so switch_mm(…) will not be
called to load the LDT at schedule()).

Switching back to a process that had a register that used the LDT will fail
since the register probably points to non-valid LDT entry (since we are
using the wrong LDT), which will lead to a segmentation fault.
 
--Shai