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SubjectRe: 3.4.0-rc1: No init found
On Tue, 10 Apr 2012 at 17:23, Benjamin Herrenschmidt wrote:
> can you test the patch below ?

When applied to 3.4-rc2, Linux boots again, yay! :-)

Tested-by: Christian Kujau <lists@nerdbynature.de>

Thanks!
Christian.

> From 08f1ec8a594c60bf3856e3c45b6d15fd691d90bb Mon Sep 17 00:00:00 2001
> From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Date: Tue, 10 Apr 2012 17:21:35 +1000
> Subject: [PATCH] powerpc: Fix page fault with lockdep regression
>
> commit a546498f3bf9aac311c66f965186373aee2ca0b0
> introduced a regression on 32-bit when irq tracing
> is enabled by exposing an old bug in our irq tracing
> code for exception entry.
>
> The code would save and restore some GPRs around the
> calls to the C lockdep code, however, it tries to be
> too smart for its own good and restores some of the
> GPRs from the exception frame (as saved there on
> exception entry).
>
> However, for page faults, we do replace those GPRs with
> arguments to do_page_fault before we call transfer_to_handler
> and so restoring from the exception frame is plain wrong in
> this case.
>
> This was fine as long as we didn't touch the interrupt state
> when taking page fault, but when I started doing it, it would
> trigger the lockdep calls and the bug.
>
> This fixes it by cleaning up that code a bit. It did create
> a small stack frame for the sake of backtraces, so let's
> make it a bit bigger and use it to save and restore the
> stuff we care about.
>
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> ---
> arch/powerpc/kernel/entry_32.S | 39 +++++++++++++++++++++------------------
> 1 file changed, 21 insertions(+), 18 deletions(-)
>
> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
> index 3e57a00..ba3aeb4 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -206,40 +206,43 @@ reenable_mmu: /* re-enable mmu so we can */
> andi. r10,r10,MSR_EE /* Did EE change? */
> beq 1f
>
> - /* Save handler and return address into the 2 unused words
> - * of the STACK_FRAME_OVERHEAD (sneak sneak sneak). Everything
> - * else can be recovered from the pt_regs except r3 which for
> - * normal interrupts has been set to pt_regs and for syscalls
> - * is an argument, so we temporarily use ORIG_GPR3 to save it
> - */
> - stw r9,8(r1)
> - stw r11,12(r1)
> - stw r3,ORIG_GPR3(r1)
> /*
> * The trace_hardirqs_off will use CALLER_ADDR0 and CALLER_ADDR1.
> * If from user mode there is only one stack frame on the stack, and
> * accessing CALLER_ADDR1 will cause oops. So we need create a dummy
> * stack frame to make trace_hardirqs_off happy.
> + *
> + * This is handy because we also need to save a bunch of GPRs,
> + * r3 can be different from GPR3(r1) at this point, r9 and r11
> + * contains the old MSR and handler address respectively,
> + * r4 & r5 can contain page fault arguments that need to be passed
> + * along as well. r12, CCR, CTR, XER etc... are left clobbered as
> + * they aren't useful past this point (aren't syscall arguments),
> + * the rest is restored from the exception frame.
> */
> + stwu r1,-32(r1)
> + stw r9,8(r1)
> + stw r11,12(r1)
> + stw r3,16(r1)
> + stw r4,20(r1)
> + stw r5,24(r1)
> andi. r12,r12,MSR_PR
> - beq 11f
> - stwu r1,-16(r1)
> + b 11f
> bl trace_hardirqs_off
> - addi r1,r1,16
> b 12f
> -
> 11:
> bl trace_hardirqs_off
> 12:
> + lwz r5,24(r1)
> + lwz r4,20(r1)
> + lwz r3,16(r1)
> + lwz r11,12(r1)
> + lwz r9,8(r1)
> + addi r1,r1,32
> lwz r0,GPR0(r1)
> - lwz r3,ORIG_GPR3(r1)
> - lwz r4,GPR4(r1)
> - lwz r5,GPR5(r1)
> lwz r6,GPR6(r1)
> lwz r7,GPR7(r1)
> lwz r8,GPR8(r1)
> - lwz r9,8(r1)
> - lwz r11,12(r1)
> 1: mtctr r11
> mtlr r9
> bctr /* jump to handler */
> --
> 1.7.9.5
>
--
BOFH excuse #292:

We ran out of dial tone and we're and waiting for the phone company to deliver another bottle.


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