On Thu, Oct 20, 2016 at 4:03 PM, Dave Jones <da...@codemonkey.org.uk> wrote: > On Thu, Oct 20, 2016 at 04:01:12PM -0700, Andy Lutomirski wrote: > > On Thu, Oct 20, 2016 at 3:50 PM, Dave Jones <da...@codemonkey.org.uk> > wrote: > > > On Tue, Oct 18, 2016 at 06:05:57PM -0700, Andy Lutomirski wrote: > > > > > > > One possible debugging approach would be to change: > > > > > > > > #define NR_CACHED_STACKS 2 > > > > > > > > to > > > > > > > > #define NR_CACHED_STACKS 0 > > > > > > > > in kernel/fork.c and to set CONFIG_DEBUG_PAGEALLOC=y. The latter will > > > > force an immediate TLB flush after vfree. > > > > > > I can give that idea some runtime, but it sounds like this a case where > > > we're trying to prove a negative, and that'll just run and run ? In > which case I > > > might do this when I'm travelling on Sunday. > > > > The idea is that the stack will be free and unmapped immediately upon > > process exit if configured like this so that bogus stack accesses (by > > the CPU, not DMA) would OOPS immediately. > > oh, misparsed. ok, I can definitely get behind that idea then. > I'll do that next. >
It could be worth trying this, too: https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/commit/?h=x86/vmap_stack&id=174531fef4e8 It occurred to me that the current code is a little bit fragile. --Andy
