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>
---
Paul, Ezequiel --
Can you verify this change addresses the problems you saw?
[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/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;
