Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [ 22/22] powerpc: Keep thread.dscr and thread.dscr_inherit in sync | Date | Fri, 14 Dec 2012 14:26:07 -0800 |
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3.0-stable review patch. If anyone has any objections, please let me know.
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From: Anton Blanchard <anton@samba.org>
commit 00ca0de02f80924dfff6b4f630e1dff3db005e35 upstream.
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 <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Haren Myneni <haren@us.ibm.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- arch/powerpc/kernel/sysfs.c | 4 +++- arch/powerpc/kernel/traps.c | 3 ++- 2 files changed, 5 insertions(+), 2 deletions(-)
--- a/arch/powerpc/kernel/sysfs.c +++ b/arch/powerpc/kernel/sysfs.c @@ -194,8 +194,10 @@ static ssize_t show_dscr_default(struct 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 sysdev_class *class, --- a/arch/powerpc/kernel/traps.c +++ b/arch/powerpc/kernel/traps.c @@ -935,8 +935,9 @@ static int emulate_instruction(struct pt 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
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