Michal Hocko <mhocko at kernel.org> writes: > On Thu 16-06-16 12:30:16, Vitaly Kuznetsov wrote: >> Christoph Hellwig <hch at infradead.org> writes: >> >> > On Thu, Jun 16, 2016 at 11:22:46AM +0200, Vitaly Kuznetsov wrote: >> >> _count -> _refcount rename in commit 0139aa7b7fa12 ("mm: rename _count, >> >> field of the struct page, to _refcount") broke kdump. makedumpfile(8) does >> >> stuff like READ_MEMBER_OFFSET("page._count", page._count) and fails. While >> >> it is definitely possible to fix this particular tool I'm not sure about >> >> other tools which might be doing the same. >> >> >> >> I suggest we remember the "we don't break userspace" rule and revert for >> >> 4.7 while it's not too late. >> > >> > Err, sorry - this is not "userspace". It's crazy crap digging into >> > kernel internal structure. >> > >> > The rename was absolutely useful, so fix up your stinking pike in kdump. >> >> Ok, sure, I'll send a patch to it. I was worried about other tools out >> there which e.g. inspect /proc/vmcore. As it is something we support >> some conservatism around it is justified. > > struct page layout as some others that such a tool might depend on has > changes several times in the past so I fail to see how is it any > different this time. IMO this time the change doesn't give us any advantage, it was just a rename. > struct page is nothing the userspace should depend on. True but at least makedumpfile(8) is special and even if it's a 'crazy crap digging into ...' we could avoid breaking it for no technical reason. -- Vitaly