David Miller writes:
> From: David Miller <davem@xxxxxxxxxxxxx>
> Date: Tue, 26 Feb 2008 16:49:00 -0800 (PST)
>
> [ Thomas, forgot to CC: you earlier, changeset
> a0c1e9073ef7428a14309cba010633a6cd6719ea ("futex: runtime enable pi
> and robust functionality") broke sparc64. ]
>
> > From: Mikael Pettersson <mikpe@xxxxxxxx>
> > Date: Tue, 26 Feb 2008 09:55:50 +0100
> >
> > > Minor update: rc2-git7 has the slow initial console behaviour,
> > > but successfully switches to the framebuffer. rc2-git8 however
> > > hangs in the console handover. So I'll bisect git7->git8 next.
> >
> > Between the VT layer registering it's console and the atyfb
> > driver initializing we get a crash, and it happens on all
> > sparc64 systems. It is caused by this commit and I am working
> > on a fix:
>
> The following patch will let things "work" but the trick being used
> here by the FUTEX layer is borderline valid in my opinion.
>
> Basically for 10+ years on sparc64 we've had this check here in the
> fault path, which makes sure that if we're processing an exception
> table entry we really, truly, are doing an access to userspace from
> the kernel. Otherwise we OOPS.
>
> What the FUTEX checking code is doing now is doing a "user" access
> with set_fs(KERNEL_DS) since it runs from the kernel bootup early init
> sequence. And this is illegal according to the existing checks.
>
> When we do set_fs(KERNEL_DS) then pass a "user" pointer down
> into a system call or something like that, we give it a pointer
> that "cannot fault". So if we get into the fault handling
> path here for a case like that we really do want to scream and
> print out an OOPS message in my opinion.
>
> I realize that not many platforms other than sparc64 can check
> for things this precisely, but it's something to consider.
>
> Did this FUTEX change go into -stable too?
>
> diff --git a/arch/sparc64/mm/fault.c b/arch/sparc64/mm/fault.c
> index e2027f2..9183633 100644
> --- a/arch/sparc64/mm/fault.c
> +++ b/arch/sparc64/mm/fault.c
> @@ -244,16 +244,8 @@ static void do_kernel_fault(struct pt_regs *regs, int si_code, int fault_code,
> if (regs->tstate & TSTATE_PRIV) {
> const struct exception_table_entry *entry;
>
> - if (asi == ASI_P && (insn & 0xc0800000) == 0xc0800000) {
> - if (insn & 0x2000)
> - asi = (regs->tstate >> 24);
> - else
> - asi = (insn >> 5);
> - }
> -
> - /* Look in asi.h: All _S asis have LS bit set */
> - if ((asi & 0x1) &&
> - (entry = search_exception_tables(regs->tpc))) {
> + entry = search_exception_tables(regs->tpc);
> + if (entry) {
> regs->tpc = entry->fixup;
> regs->tnpc = regs->tpc + 4;
> return;
>
Thanks, 2.6.25-rc3 plus this patch works fine on my Ultra5.
/Mikael
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