During a context switch we always restore the per thread DSCR value. If we aren't doing explicit DSCR management (ie thread.dscr_inherit == 0) and the default DSCR changed while the process has been sleeping we end up with the wrong value.
Check thread.dscr_inherit and select the default DSCR or per thread DSCR as required. This was found with the following test case, when running with more threads than CPUs (ie forcing context switching): http://ozlabs.org/~anton/junkcode/dscr_default_test.c With the four patches applied I can run a combination of all test cases successfully at the same time: http://ozlabs.org/~anton/junkcode/dscr_default_test.c http://ozlabs.org/~anton/junkcode/dscr_explicit_test.c http://ozlabs.org/~anton/junkcode/dscr_inherit_test.c Signed-off-by: Anton Blanchard <an...@samba.org> Cc: <sta...@kernel.org> # 3.0+ --- Index: b/arch/powerpc/kernel/entry_64.S =================================================================== --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -370,6 +370,12 @@ _GLOBAL(ret_from_fork) li r3,0 b syscall_exit + .section ".toc","aw" +DSCR_DEFAULT: + .tc dscr_default[TC],dscr_default + + .section ".text" + /* * This routine switches between two different tasks. The process * state of one is saved on its kernel stack. Then the state @@ -509,9 +515,6 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEG mr r1,r8 /* start using new stack pointer */ std r7,PACAKSAVE(r13) - ld r6,_CCR(r1) - mtcrf 0xFF,r6 - #ifdef CONFIG_ALTIVEC BEGIN_FTR_SECTION ld r0,THREAD_VRSAVE(r4) @@ -520,14 +523,22 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC) #endif /* CONFIG_ALTIVEC */ #ifdef CONFIG_PPC64 BEGIN_FTR_SECTION + lwz r6,THREAD_DSCR_INHERIT(r4) + ld r7,DSCR_DEFAULT@toc(2) ld r0,THREAD_DSCR(r4) - cmpd r0,r25 - beq 1f + cmpwi r6,0 + bne 1f + ld r0,0(r7) +1: cmpd r0,r25 + beq 2f mtspr SPRN_DSCR,r0 -1: +2: END_FTR_SECTION_IFSET(CPU_FTR_DSCR) #endif + ld r6,_CCR(r1) + mtcrf 0xFF,r6 + /* r3-r13 are destroyed -- Cort */ REST_8GPRS(14, r1) REST_10GPRS(22, r1) Index: b/arch/powerpc/kernel/asm-offsets.c =================================================================== --- a/arch/powerpc/kernel/asm-offsets.c +++ b/arch/powerpc/kernel/asm-offsets.c @@ -76,6 +76,7 @@ int main(void) DEFINE(SIGSEGV, SIGSEGV); DEFINE(NMI_MASK, NMI_MASK); DEFINE(THREAD_DSCR, offsetof(struct thread_struct, dscr)); + DEFINE(THREAD_DSCR_INHERIT, offsetof(struct thread_struct, dscr_inherit)); #else DEFINE(THREAD_INFO, offsetof(struct task_struct, stack)); #endif /* CONFIG_PPC64 */ _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
