On Tue, Feb 5, 2019 at 8:14 AM Jan Stancek <jstan...@redhat.com> wrote: > Hi, > > are you using THP (CONFIG_TRANSPARENT_HUGEPAGE)? > > The changed line should affect only THP and normal compound pages, > so a test with THP disabled might be interesting. > > > > > The breakage consists of random processes dying with SIGILL or SIGSEGV > > when we stress test the system with high memory pressure and explicit > > memory compaction requested through /proc/sys/vm/compact_memory. > > Reverting this patch fixes the crashes. > > > > We can put some effort on debugging if there are no obvious > > explanations for this. Keep in mind that this is 32-bit system with > > HIGHMEM. > > Nothing obvious that I can see. I've been trying to reproduce on > 32-bit x86 Fedora with no luck so far. >
Hi Thanks for looking in to it. After some deep dive in MM code, I think it is safe to say this patch was innocent. All traces studied so far points to a missing cache coherency call in mm/migrate.c:migrate_page that is needed only for those evil MIPSes that lack I/D cache coherency. I will send a write-up to linux-mips about this. Basically for a non-mapped page it does only a copy of page data and metadata but no flush_dcache_page() call will be done. This races with subsequent use of the page. BR, Lars