Ian Kent wrote:
On Fri, 18 Nov 2005, William H. Taber wrote:
No, it is actually a little more subtle than that. The problem is that since
you can be called from two code paths, one of which get's the lock and one of
them doesn't, you are stuck if you find that the lock is held because you
don't know who holds it. The danger is that some innocent third party is
holding the lock and counting on being protected by it. If you release the
lock, then you can be creating the potential for a race in their code and
there would be no way to detect it. Their code path would look correct
because it is. Not only that but the lock itself could get confused because
it would have more unlocks than locks, because presumably the process that
thinks it has the lock would eventually unlock as well. I don't know how the
semaphores are implemented on all architectures so I don't know if that would
be an actual problem or not but it I would be surprised if they all handled
that case gracefully.
Yes. Thinking about it I hadn't considered the third process.
How can we get advice on this?
Ian
Hey, I'm new here. I came here looking for advice. :^)
However, if there is no way to fix this in the autofs code then the only
alternative is to fix the locking in the VFS. So VFS folks, which is
the better solution. Should all callers to d_revalidate get the
parent's i_sem lock or should d_revalidate never be called with the
parent i_sem lock and so we need to change lookup_one_len so that it
does not expect the parent i_sem lock to be held?
Will Taber
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