Re: ipc,sem: sysv semaphore scalability

[Linus Torvalds]

On Fri, Mar 29, 2013 at 2:12 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> I dunno. I'm still not sure this is triggerable, but it looks bad. But
> both the semaphore case and the msg cases seem to be solvable by
> moving the unlock down, and shm seem to have no getref/putref users to
> race with, so this (whitespace-damaged) patch *may* be sufficient:

Well, the patch doesn't seem to cause any problems, at least neither
lockdep nor spinlock sleep debugging complains. I have no idea whether
it actually fixes any problems, though.

I do wonder if this might explain the problem Emmanuel saw. A double
free of a RCU-freeable object would possibly result in exactly the
kind of mess that Emmanuel reported with the semaphore scalability
patches.

Emmanuel, can you try the attached patch? I think it applies cleanly
on top of the scalability series too without any changes, but I didn't
check if the patches perhaps changed some of the naming or something.

              Linus

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