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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 <anton@samba.org>
Cc: <stable@kernel.org> # 3.0+
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Anton Blanchard 2012-09-03 16:48:46 +00:00 committed by Benjamin Herrenschmidt
parent 1b6ca2a6fe
commit 00ca0de02f
2 changed files with 5 additions and 2 deletions
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4
arch/powerpc/kernel/sysfs.c
View File

@ -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,

3
arch/powerpc/kernel/traps.c
View File

@ -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