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SubjectRe: kernel: ldt allocation failed
At 09:15 07/12/01, Alan Cox wrote:
> > I don't see how one can magically tell that this is an NVIDIA problem.
>
>We don't know. But since we don't have their source and they have our
>source only they can tell you.

Not doing any debugging is fine.

However, looking at 2.4.16/arch/i386/kernel/process.c::copy_segments()
which generates this message it seems odd: It returns void, yet it can fail
because it is doing a vmalloc().

When the vmalloc() fails, the new_mm->context.segments is set to NULL and
the function returns.

That seems wrong, no? Shouldn't there be a panic() when the allocation
fails at least? Or even better the function should perhaps return an error
code?

Considering there is only one caller (kernel/fork.c::copy_mm()) it would be
easy to modify copy_mm() to handle a returned error code gracefully and
goto fail_nomem, which would in turn result in kernel/fork.c::do_fork(),
the only caller of copy_mm(), cleaning up properly and returning an error code.

Or have I missed something and the situation where the ldt is missing can
be recovered from? - I would think (without looking into this in the kernel
code) that loosing the local descriptor table would be rather detrimental
on the first context switch to the new process created by fork... And
considering all kinds of errors are being handled in this code path, except
for the vmalloc() failure, it seems like a good idea to add the appropriate
fail mechanism.

If nvidia is causing this to get triggered they will likely run into
problems elsewhere anyway and we don't care but we should get the kernel
working. As it is AFAICS we have a potential DOS, just get the box close to
OOM and start calling man 2 fork and/or man 3 clone and you could trigger
this with a finite probability.

Best regards,

Anton


--
"I've not lost my mind. It's backed up on tape somewhere." - Unknown
--
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Linux NTFS Maintainer / WWW: http://linux-ntfs.sf.net/
ICQ: 8561279 / WWW: http://www-stu.christs.cam.ac.uk/~aia21/

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