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

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commit 00ca0de02f 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>
This commit is contained in:
Anton Blanchard
2012-09-03 16:48:46 +00:00
committed by Greg Kroah-Hartman
parent 1758e55fd0
commit 3882a18f5f
2 changed files with 5 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
arch/powerpc/kernel/sysfs.c
View File

@@ -194,8 +194,10 @@ static ssize_t show_dscr_default(struct sysdev_class *class,
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,

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

@@ -935,8 +935,9 @@ 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