On Thu, 2011-07-21 at 15:36 -0700, Andrew Morton wrote: > On Tue, 19 Jul 2011 14:29:22 +1000 > Benjamin Herrenschmidt <b...@kernel.crashing.org> wrote: > > > The futex code currently attempts to write to user memory within > > a pagefault disabled section, and if that fails, tries to fix it > > up using get_user_pages(). > > > > This doesn't work on archs where the dirty and young bits are > > maintained by software, since they will gate access permission > > in the TLB, and will not be updated by gup(). > > > > In addition, there's an expectation on some archs that a > > spurious write fault triggers a local TLB flush, and that is > > missing from the picture as well. > > > > I decided that adding those "features" to gup() would be too much > > for this already too complex function, and instead added a new > > simpler fixup_user_fault() which is essentially a wrapper around > > handle_mm_fault() which the futex code can call. > > > > Signed-off-by: Benjamin Herrenschmidt <b...@kernel.crashing.org> > > --- > > > > Shan, can you test this ? It might not fix the problem > > um, what problem. There's no description here of the user-visible > effects of the bug hence it's hard to work out what kernel version(s) > should receive this patch.
Shan could give you an actual example (it was in the previous thread), but basically, livelock as the kernel keeps trying and trying the in_atomic op and never resolves it. > What kernel version(s) should receive this patch? I haven't dug. Probably anything it applies on as far as we did that trick of atomic + gup() for futex. > > since I'm > > starting to have the nasty feeling that you are hitting what is > > somewhat a subtly different issue or my previous patch should > > have worked (but then I might have done a stupid mistake as well) > > but let us know anyway. > > I assume that Shan reported the secret problem so I added the > reported-by to the changelog. He did :-) Shan, care to provide a rough explanation of what you observed ? Also Russell confirmed that ARM should be affected as well. Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
