powerpc: Keep thread.dscr and thread.dscr_inherit in sync

When we update the DSCR either via emulation of mtspr(DSCR) or via a change to dscr_default in sysfs we don't update thread.dscr. We will eventually update it at context switch time but there is a period where thread.dscr is incorrect. If we fork at this point we will copy the old value of thread.dscr into the child. To avoid this, always keep thread.dscr in sync with reality. This issue was found with the following testcase: http://ozlabs.org/~anton/junkcode/dscr_inherit_test.c

Anton Blanchard committed 14 years ago

Commit 00ca0de1 parent 1b6ca2a2 files · +5 −2Browse files

Unified · Split

2 files

arch/powerpc/kernel/sysfs.c +3 −1
arch/powerpc/kernel/traps.c +2 −1

arch/powerpc/kernel/sysfs.c+3−1

@@ -196,8 +196,10 @@ static ssize_t show_dscr_default(struct device *dev, · 195 unmodified lines
196	196
197	197	static void update_dscr(void *dummy)
198	198	{
199		− if (!current->thread.dscr_inherit)
	199	+ if (!current->thread.dscr_inherit) {
	200	+ current->thread.dscr = dscr_default;
200	201	mtspr(SPRN_DSCR, dscr_default);
	202	+ }
201	203	}
202	204
203	205	static ssize_t __used store_dscr_default(struct device *dev,

arch/powerpc/kernel/traps.c+2−1

@@ -972,8 +972,9 @@ static int emulate_instruction(struct pt_regs *regs) · 971 unmodified lines
972	972	cpu_has_feature(CPU_FTR_DSCR)) {
973	973	PPC_WARN_EMULATED(mtdscr, regs);
974	974	rd = (instword >> 21) & 0x1f;
975		− mtspr(SPRN_DSCR, regs->gpr[rd]);
	975	+ current->thread.dscr = regs->gpr[rd];
976	976	current->thread.dscr_inherit = 1;
	977	+ mtspr(SPRN_DSCR, current->thread.dscr);
977	978	return 0;
978	979	}
979	980	#endif