Messages in this thread | | | Date | Wed, 12 Oct 2005 14:17:32 -0400 | From | Janak Desai <> | Subject | Re: [PATCH] New System call unshare (try 2) |
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Jamie Lokier wrote: > Janak Desai wrote: > >> Don't allow namespace unsharing, if sharing fs (CLONE_FS) > > > Makes sense. clone() has the same test at the start. (I think > namespace should be a property of fs, not task, anyway. Or completely > eliminated because it's implied by the task's root dentry+vfsmnt). > > >> Don't allow sighand unsharing if not unsharing vm > > > Why not? It's permitted to clone with unshared sighand and shared vm, > and it's useful too. > > It's the combination shared sighand + unshared vm which is not > allowed by clone - so I think that's what you should refuse. >
Yes, thanks. I had that backwards. I am checking for the illegal combination of "shared sighand + unshared vm" later but I will allow (and test) unsharing of sighand while keeping shared vm.
> >> Don't allow vm unsharing if task cloned with CLONE_THREAD > > > It would be better to do what clone does, and say "don't allow sighand > unsharing if task cloned with CLONE_THREAD". This is because > CLONE_THREAD tasks must have shared signals. > > In combination with the rule above for sighand (my rule, not yours), > that implies "don't allow vm unsharing.." as a consequence. >
Ok. Basically, with my current logic you are forced to unshare both vm and sighand. I will update so you can unshare just sighand and tie the CLONE_THREAD restriction to sighand.
> >> Don't allow vm unsharing if the task is performing async io > > > Why not? > > Async ios are tied to an mm (see lookup_ioctx in fs/aio.c), which may > be shared among tasks. I see no reason why the async ios can't > continue and be waited in on in other tasks that may be using the old mm. > > The new mm, if vm is unshared, would simply not see the outstanding > aios - in the same way as if a vm was unshared by fork(). >
Yes, I did see that async ios are tied to an mm and that aio context is cleared when a new mm is created by clone/exec. It just appeared odd to me that a task that setup aio is unable to continue performing aio after unsharing mm, but the task that it was sharing mm with, can. I don't have any problem making this change. It's just that I wasn't sure about aio usage and thought it was better to not allow an mm unshare if aio is being performed.
-Janak
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