From 00ca0de02f80924dfff6b4f630e1dff3db005e35 Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Mon, 3 Sep 2012 16:48:46 +0000 Subject: [PATCH] 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 Signed-off-by: Anton Blanchard Cc: # 3.0+ Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/kernel/sysfs.c | 4 +++- arch/powerpc/kernel/traps.c | 3 ++- 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c index d4cbbd1..8302af6 100644 --- a/arch/powerpc/kernel/sysfs.c +++ b/arch/powerpc/kernel/sysfs.c @@ -196,8 +196,10 @@ static ssize_t show_dscr_default(struct device *dev, static void update_dscr(void *dummy) { - if (!current->thread.dscr_inherit) + if (!current->thread.dscr_inherit) { + current->thread.dscr = dscr_default; mtspr(SPRN_DSCR, dscr_default); + } } static ssize_t __used store_dscr_default(struct device *dev, diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c index 1589723..ae0843f 100644 --- a/arch/powerpc/kernel/traps.c +++ b/arch/powerpc/kernel/traps.c @@ -972,8 +972,9 @@ static int emulate_instruction(struct pt_regs *regs) cpu_has_feature(CPU_FTR_DSCR)) { PPC_WARN_EMULATED(mtdscr, regs); rd = (instword >> 21) & 0x1f; - mtspr(SPRN_DSCR, regs->gpr[rd]); + current->thread.dscr = regs->gpr[rd]; current->thread.dscr_inherit = 1; + mtspr(SPRN_DSCR, current->thread.dscr); return 0; } #endif -- 2.7.4