Messages in this thread | | | Date | Mon, 10 Dec 2012 20:12:32 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 3/7] uprobes: Kill the pointless inode/uc checks in register/unregister |
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On 12/10, Srikar Dronamraju wrote: > > * Oleg Nesterov <oleg@redhat.com> [2012-11-23 21:28:06]: > > > register/unregister verifies that inode/uc != NULL. For what? > > This really looks like "hide the potential problem", the caller > > should pass the valid data. > > > > Agree that users should pass valid data. > I do understand that we expect the users to be knowledge-able. > Also users are routed thro in-kernel api that does this check. > > However from an api perspective, if a user passes invalid data, do we > want the system to crash. > > Esp if kernel can identify that users has indeed passed wrong info. I do agree > that users can still pass invalid data that kernel maynot be able to > identify in most cases.
inode != NULL can't verify that it actually points to the valid inode, NULL is only one example of invalid data.
I agree, sometimes it makes sense to protect against the stupid mistakes, but if we want to check against NULL we should do
if (WARN_ON(!inode)) return;
Especially in uprobe_unregister(). The current code is really "hide the possible problem" and nothing more. It is better to crash imho than silently return.
> > register() also checks uc->next == NULL, probably to prevent the > > double-register but the caller can do other stupid/wrong things. > > Users can surely do more stupid things. But this is again something that > kernel can identify. By allowing a double-register of a consumer, thats > already registered, we might end up allowing circular loop of consumers.
I understand. But in this case we should document that uc->next must be cleared before uprobe_register(). Or add init_consumer().
And we should change uprobe_unregister() to clear uc->next as well. I think that the code like this
uprobe_register(uc); uprobe_unregister(uc);
uprobe_register(uc);
should work. Currently it doesn't because of this check.
So I still think these checks are pointless and (at least in unregister) even harmful.
But I won't insist too much, I can drop this patch if you do not change your mind.
Oleg.
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