Subject: Re: lowlatency patch question
From: Arjan van de Ven <arjanv@redhat.com>
Reply-To: arjanv@redhat.com
To: shai@ftcon.com
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <200401110331.BBB99015@ms6.verisignmail.com>
References: <200401110331.BBB99015@ms6.verisignmail.com>
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Organization: Red Hat, Inc.
Message-Id: <1073814493.4431.1.camel@laptop.fenrus.com>
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Date: Sun, 11 Jan 2004 10:48:14 +0100
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> 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 wi=
ll
> not use the right LDT (since tsk->mm was zeroed, so switch_mm() will not =
be
> called to load the LDT at schedule()).

since closing of files can sleep anyway I don't see how this schedule
point could introduce a bug.


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

Do you have an oops? Could you file that in RH bugzilla
(bugzilla.redhat.com) ? RH bugzilla is a far more appropriate place to
report bugs in the RH vendor kernels than lkml is.

Greetings,
   Arjan van de Ven

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