From: <shai@ftcon.com>
Message-Id: <200401110331.BBB99015@ms6.verisignmail.com>
Reply-To: <shai@ftcon.com>
To: <linux-kernel@vger.kernel.org>
Subject: lowlatency patch question
Date: Sat, 10 Jan 2004 19:31:47 -0800
Organization: FT Consulting
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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


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