Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM)

On Tue, Feb 23, 2016 at 10:33:45PM +0300, Kirill A. Shutemov wrote:

On Tue, Feb 23, 2016 at 07:19:07PM +0100, Gerald Schaefer wrote:

quoted

I'll check with Martin, maybe it is actually trivial, then we can
do a quick test it to rule that one out.

Oh. I found a bug in __split_huge_pmd_locked(). Although, not sure if it's
_the_ bug.

pmdp_invalidate() is called for the wrong address :-/
I guess that can be destructive on the architecture, right?

FWIW, arm64 ignores the address parameter for set_pmd_at, so this would
only result in the TLBI nuking the wrong entries, which is going to be
tricky to observe in practice given that we install a table entry
immediately afterwards that maps the same pages. If s390 does more here
(I see some magic asm using the address), that could be the answer...

Will