On Fri, 2011-07-15 at 11:32 -0400, Shan Hai wrote:I agree with you, the problem could be triggered by accessingBut we can't. The must not modify the PTE from an interrupt context and
any user space page which has kernel read only permission
in the page fault disabled context, the problem also affects
architectures which depend on SW dirty/young tracking as
stated by Benjamin in this thread.
In the e500 case, the commit 6cfd8990e27d3a491c1c605d6cbc18a46ae51fef
removed the write permission fixup from TLB miss handlers and left it to
generic code, so it might be right time to fixup the write permission here
in the generic code.
the "atomic" variants of user accesses can be called in such contexts.
I think the problem is that we try to actually do things other than just
"peek" at user memory (for backtraces etc...) but actually useful things
in page fault disabled contexts. That's bad and various archs mm were
designed with the assumption that this never happens.
If the futex case is seldom here, we could probably find a way to work
around in that specific case.
However, I -still- don't understand why gup didn't fixup the write
permission. gup doesn't set dirty ?