Re: [PATCH powerpc] fix unpaired __trace_hcall_entry and __trace_hcall_exit

Benjamin Herrenschmidt
2012-01-03T00:54:38Z

On Mon, 2011-12-19 at 10:06 +0800, Li Zhong wrote:
> Unpaired calling of __trace_hcall_entry and __trace_hcall_exit could
> cause incorrect preempt count. And it might happen as the global
> variable hcall_tracepoint_refcount is checked separately before calling
> them.
>
> I don't know much about the powerpc arch. But the idea here is to store
> the hcall_tracepoint_refcount locally, so __trace_hcall_entry and
> __trace_hcall_exit will be called or not called in pair by checking the
> same value.

Can you re-use an existing spot in the stack frame rather than adding
this entry ? There's plenty of unused spots :-) For example the link
editor doubleword is never going to be used in that function, we could
hijack it safely. It would make the patch (and the code) simpler.

Cheers,
Ben.

> Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>
> Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
> arch/powerpc/platforms/pseries/hvCall.S | 20 +++++++++++---------
> 1 files changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pseries/hvCall.S b/arch/powerpc/platforms/pseries/hvCall.S
> index fd05fde..1240bd2 100644
> --- a/arch/powerpc/platforms/pseries/hvCall.S
> +++ b/arch/powerpc/platforms/pseries/hvCall.S
> @@ -14,6 +14,7 @@
> #include <asm/ptrace.h>
>
> #define STK_PARM(i) (48 + ((i)-3)*8)
> +#define REG_SIZE (2*8)
>
> #ifdef CONFIG_TRACEPOINTS
>
> @@ -32,11 +33,12 @@ hcall_tracepoint_refcount:
> * unconditional cpu feature.
> */
> #define HCALL_INST_PRECALL(FIRST_REG) \
> + std r31,-8(r1); \
> BEGIN_FTR_SECTION; \
> b 1f; \
> END_FTR_SECTION(0, 1); \
> - ld r12,hcall_tracepoint_refcount@toc(r2); \
> - cmpdi r12,0; \
> + ld r31,hcall_tracepoint_refcount@toc(r2); \
> + cmpdi r31,0; \
> beq+ 1f; \
> mflr r0; \
> std r3,STK_PARM(r3)(r1); \
> @@ -49,9 +51,9 @@ END_FTR_SECTION(0, 1); \
> std r10,STK_PARM(r10)(r1); \
> std r0,16(r1); \
> addi r4,r1,STK_PARM(FIRST_REG); \
> - stdu r1,-STACK_FRAME_OVERHEAD(r1); \
> + stdu r1,-STACK_FRAME_OVERHEAD-REG_SIZE(r1); \
> bl .__trace_hcall_entry; \
> - addi r1,r1,STACK_FRAME_OVERHEAD; \
> + addi r1,r1,STACK_FRAME_OVERHEAD+REG_SIZE; \
> ld r0,16(r1); \
> ld r3,STK_PARM(r3)(r1); \
> ld r4,STK_PARM(r4)(r1); \
> @@ -74,8 +76,7 @@ END_FTR_SECTION(0, 1); \
> BEGIN_FTR_SECTION; \
> b 1f; \
> END_FTR_SECTION(0, 1); \
> - ld r12,hcall_tracepoint_refcount@toc(r2); \
> - cmpdi r12,0; \
> + cmpdi r31,0; \
> beq+ 1f; \
> mflr r0; \
> ld r6,STK_PARM(r3)(r1); \
> @@ -83,13 +84,14 @@ END_FTR_SECTION(0, 1); \
> mr r4,r3; \
> mr r3,r6; \
> std r0,16(r1); \
> - stdu r1,-STACK_FRAME_OVERHEAD(r1); \
> + stdu r1,-STACK_FRAME_OVERHEAD-REG_SIZE(r1); \
> bl .__trace_hcall_exit; \
> - addi r1,r1,STACK_FRAME_OVERHEAD; \
> + addi r1,r1,STACK_FRAME_OVERHEAD+REG_SIZE; \
> ld r0,16(r1); \
> ld r3,STK_PARM(r3)(r1); \
> mtlr r0; \
> -1:
> +1: \
> + ld r31,-8(r1);
>
> #define HCALL_INST_POSTCALL_NORETS \
> li r5,0; \