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powerpc: Fix DSCR inheritance in copy_thread() 

If the default DSCR is non zero we set thread.dscr_inherit in
copy_thread() meaning the new thread and all its children will ignore
future updates to the default DSCR. This is not intended and is
a change in behaviour that a number of our users have hit.

We just need to inherit thread.dscr and thread.dscr_inherit from
the parent which ends up being much simpler.

This was found with the following test case:

http://ozlabs.org/~anton/junkcode/dscr_default_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 16:49:47 +00:00 committed by Benjamin Herrenschmidt
parent 00ca0de02f
commit 1021cb268b
1 changed files with 2 additions and 10 deletions
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12
arch/powerpc/kernel/process.c
View File

@ -802,16 +802,8 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
#endif /* CONFIG_PPC_STD_MMU_64 */
#ifdef CONFIG_PPC64
if (cpu_has_feature(CPU_FTR_DSCR)) {
if (current->thread.dscr_inherit) {
p->thread.dscr_inherit = 1;
p->thread.dscr = current->thread.dscr;
} else if (0 != dscr_default) {
p->thread.dscr_inherit = 1;
p->thread.dscr = dscr_default;
} else {
p->thread.dscr_inherit = 0;
p->thread.dscr = 0;
}
p->thread.dscr_inherit = current->thread.dscr_inherit;
p->thread.dscr = current->thread.dscr;
}
#endif