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powerpc: Restore correct DSCR in context switch

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During a context switch we always restore the per thread DSCR value.
If we aren't doing explicit DSCR management
(ie thread.dscr_inherit == 0) and the default DSCR changed while
the process has been sleeping we end up with the wrong value.

Check thread.dscr_inherit and select the default DSCR or per thread
DSCR as required.

This was found with the following test case, when running with
more threads than CPUs (ie forcing context switching):

http://ozlabs.org/~anton/junkcode/dscr_default_test.c

With the four patches applied I can run a combination of all
test cases successfully at the same time:

http://ozlabs.org/~anton/junkcode/dscr_default_test.c
http://ozlabs.org/~anton/junkcode/dscr_explicit_test.c
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 16:51:10 +00:00 committed by Benjamin Herrenschmidt
parent 1021cb268b
commit 714332858b
2 changed files with 18 additions and 6 deletions
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1
arch/powerpc/kernel/asm-offsets.c
View File

@ -76,6 +76,7 @@ int main(void)
DEFINE(SIGSEGV, SIGSEGV);
DEFINE(NMI_MASK, NMI_MASK);
DEFINE(THREAD_DSCR, offsetof(struct thread_struct, dscr));
DEFINE(THREAD_DSCR_INHERIT, offsetof(struct thread_struct, dscr_inherit));
#else
DEFINE(THREAD_INFO, offsetof(struct task_struct, stack));
#endif /* CONFIG_PPC64 */

23
arch/powerpc/kernel/entry_64.S
View File

@ -370,6 +370,12 @@ _GLOBAL(ret_from_fork)
li r3,0
b syscall_exit
.section ".toc","aw"
DSCR_DEFAULT:
.tc dscr_default[TC],dscr_default
.section ".text"
/*
* This routine switches between two different tasks. The process
* state of one is saved on its kernel stack. Then the state
@ -509,9 +515,6 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT)
mr r1,r8 /* start using new stack pointer */
std r7,PACAKSAVE(r13)
ld r6,_CCR(r1)
mtcrf 0xFF,r6
#ifdef CONFIG_ALTIVEC
BEGIN_FTR_SECTION
ld r0,THREAD_VRSAVE(r4)
@ -520,14 +523,22 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
#endif /* CONFIG_ALTIVEC */
#ifdef CONFIG_PPC64
BEGIN_FTR_SECTION
lwz r6,THREAD_DSCR_INHERIT(r4)
ld r7,DSCR_DEFAULT@toc(2)
ld r0,THREAD_DSCR(r4)
cmpd r0,r25
beq 1f
cmpwi r6,0
bne 1f
ld r0,0(r7)
1: cmpd r0,r25
beq 2f
mtspr SPRN_DSCR,r0
1:
2:
END_FTR_SECTION_IFSET(CPU_FTR_DSCR)
#endif
ld r6,_CCR(r1)
mtcrf 0xFF,r6
/* r3-r13 are destroyed -- Cort */
REST_8GPRS(14, r1)
REST_10GPRS(22, r1)