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powerpc: Update DSCR on all CPUs when writing sysfs dscr_default 

Writing to dscr_default in sysfs doesn't actually change the DSCR -
we rely on a context switch on each CPU to do the work. There is no
guarantee we will get a context switch in a reasonable amount of time
so fire off an IPI to force an immediate change.

This issue was found with the following test case:

http://ozlabs.org/~anton/junkcode/dscr_explicit_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 16:47:56 +00:00 committed by Benjamin Herrenschmidt
parent 375f561a41
commit 1b6ca2a6fe
1 changed files with 8 additions and 0 deletions
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8
arch/powerpc/kernel/sysfs.c
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@ -194,6 +194,12 @@ static ssize_t show_dscr_default(struct device *dev,
return sprintf(buf, "%lx\n", dscr_default);
}
static void update_dscr(void *dummy)
{
if (!current->thread.dscr_inherit)
mtspr(SPRN_DSCR, dscr_default);
}
static ssize_t __used store_dscr_default(struct device *dev,
struct device_attribute *attr, const char *buf,
size_t count)
@ -206,6 +212,8 @@ static ssize_t __used store_dscr_default(struct device *dev,
return -EINVAL;
dscr_default = val;
on_each_cpu(update_dscr, NULL, 1);
return count;
}