Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon_vmasof a mergeable VMA

From: Linus Torvalds
Date: Wed Apr 07 2010 - 18:14:53 EST

On Wed, 7 Apr 2010, Rik van Riel wrote:
> One of the issues with your patch is that anon_vma_prepare
> can fail and this patch ignores its return value.

Yes. The failure point is too late to do anything really interesting with,
and the old code also just causes a SIGBUS. My intention was to change the


into returning that SIGBUS - which is not wonderful, but is no different
from old failures.

In the long run, it would be nicer to actually return an error from the
mmap() that fails, but that's more complicated, and as mentioned, it's not
what the old code used to do either (since the failure point was always at
the page fault stage).

> Having anon_vma-prepare fail after an mremap or mprotect
> might result in messing up the VMAs of a process, or having
> to undo the VMA changes that were made.

We really aren't any worse off than we have always been.

If anon_vma_prepare() fails, the vma list will be valid, but no new pages
can be added to that vma. That used to be true before too.

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