On 05/12/2015 11:20 AM, Maciej W. Rozycki wrote:
> Fix "BUG: using smp_processor_id() in preemptible" reported in accesses
> to thread's FPU defaults: the value to initialise FSCR to at program
> startup, the FCSR r/w mask and the contents of FIR in full FPU
> emulation, removing a regression introduced with 9b26616c [MIPS: Respect
> the ISA level in FCSR handling] and f6843626 [MIPS: math-emu: Set FIR
> feature flags for full emulation].
>
> Use `boot_cpu_data' to obtain the data from, following the approach that
> `cpu_has_*' macros take and avoiding the call to `smp_processor_id' made
> in the reference to `current_cpu_data'. The contents of FSCR have to be
> consistent across processors in an SMP system, the settings there must
> not change as a thread is migrated across processors. And the contents
> of FIR are guaranteed to be consistent in FPU emulation, by definition.
>
> Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxxxxx>
> ---
> Changes from v1:
>
> - also fix PTRACE_SETFPREGS (thanks, Paul!).
>
> Paul, Ezequiel --
>
> Can you verify this change addresses the problems you saw?
>
Tested-by: Ezequiel Garcia <ezequiel.garcia@xxxxxxxxxx>
> [Ralf, this is another 4.1 material, please push it to Linus ASAP, once
> this has been confirmed to DTRT.]
>
> Thanks,
>
> Maciej
>
> linux-mips-emu-fcsr-isa-fix.diff
> Index: linux-org-test/arch/mips/include/asm/elf.h
> ===================================================================
> --- linux-org-test.orig/arch/mips/include/asm/elf.h 2015-05-06 23:20:51.946503000 +0100
> +++ linux-org-test/arch/mips/include/asm/elf.h 2015-05-12 14:37:14.169350000 +0100
> @@ -304,7 +304,7 @@ do { \
> \
> current->thread.abi = &mips_abi; \
> \
> - current->thread.fpu.fcr31 = current_cpu_data.fpu_csr31; \
> + current->thread.fpu.fcr31 = boot_cpu_data.fpu_csr31; \
> } while (0)
>
> #endif /* CONFIG_32BIT */
> @@ -366,7 +366,7 @@ do { \
> else \
> current->thread.abi = &mips_abi; \
> \
> - current->thread.fpu.fcr31 = current_cpu_data.fpu_csr31; \
> + current->thread.fpu.fcr31 = boot_cpu_data.fpu_csr31; \
> \
> p = personality(current->personality); \
> if (p != PER_LINUX32 && p != PER_LINUX) \
> Index: linux-org-test/arch/mips/kernel/ptrace.c
> ===================================================================
> --- linux-org-test.orig/arch/mips/kernel/ptrace.c 2015-04-28 14:52:04.000000000 +0100
> +++ linux-org-test/arch/mips/kernel/ptrace.c 2015-05-12 15:12:03.511002000 +0100
> @@ -176,7 +176,7 @@ int ptrace_setfpregs(struct task_struct
>
> __get_user(value, data + 64);
> fcr31 = child->thread.fpu.fcr31;
> - mask = current_cpu_data.fpu_msk31;
> + mask = boot_cpu_data.fpu_msk31;
> child->thread.fpu.fcr31 = (value & ~mask) | (fcr31 & mask);
>
> /* FIR may not be written. */
> Index: linux-org-test/arch/mips/math-emu/cp1emu.c
> ===================================================================
> --- linux-org-test.orig/arch/mips/math-emu/cp1emu.c 2015-04-28 14:52:04.000000000 +0100
> +++ linux-org-test/arch/mips/math-emu/cp1emu.c 2015-05-12 14:41:06.308256000 +0100
> @@ -889,7 +889,7 @@ static inline void cop1_cfc(struct pt_re
> break;
>
> case FPCREG_RID:
> - value = current_cpu_data.fpu_id;
> + value = boot_cpu_data.fpu_id;
> break;
>
> default:
> @@ -921,7 +921,7 @@ static inline void cop1_ctc(struct pt_re
> (void *)xcp->cp0_epc, MIPSInst_RT(ir), value);
>
> /* Preserve read-only bits. */
> - mask = current_cpu_data.fpu_msk31;
> + mask = boot_cpu_data.fpu_msk31;
> fcr31 = (value & ~mask) | (fcr31 & mask);
> break;
>
>
--
Ezequiel
