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ARC: [SMP] Fix build failures for large NR_CPUS 

ST.as only takes S9 (255) for offset. This was going out of range when
accessing a task_struct field with 4k NR_CPUS (due to 128b of coumaks
itself in there).

Workaround by using an intermediate register to do the address scaling.

There is some duplication of fix for ctx_sw.c and ctx_sw_asm.S however
given that C version will go away soon I'm not bothering to factor out
the common code.

Reported-by: Noam Camus <noamc@ezchip.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
This commit is contained in:
Vineet Gupta 2013-11-01 10:46:40 +05:30
parent 3aa4f80e41
commit 57e26e5745
2 changed files with 21 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
arch/arc/kernel/ctx_sw.c
View File

@ -17,6 +17,8 @@
#include <asm/asm-offsets.h>
#include <linux/sched.h>
#define KSP_WORD_OFF ((TASK_THREAD + THREAD_KSP) / 4)
struct task_struct *__sched
__switch_to(struct task_struct *prev_task, struct task_struct *next_task)
{
@ -45,7 +47,16 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
#endif
/* set ksp of outgoing task in tsk->thread.ksp */
#if KSP_WORD_OFF <= 255
"st.as sp, [%3, %1] \n\t"
#else
/*
* Workaround for NR_CPUS=4k
* %1 is bigger than 255 (S9 offset for st.as)
*/
"add2 r24, %3, %1 \n\t"
"st sp, [r24] \n\t"
#endif
"sync \n\t"
@ -97,7 +108,7 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
/* FP/BLINK restore generated by gcc (standard func epilogue */
: "=r"(tmp)
: "n"((TASK_THREAD + THREAD_KSP) / 4), "r"(next), "r"(prev)
: "n"(KSP_WORD_OFF), "r"(next), "r"(prev)
: "blink"
);

11
arch/arc/kernel/ctx_sw_asm.S
View File

@ -14,6 +14,8 @@
#include <asm/asm-offsets.h>
#include <asm/linkage.h>
#define KSP_WORD_OFF ((TASK_THREAD + THREAD_KSP) / 4)
;################### Low Level Context Switch ##########################
.section .sched.text,"ax",@progbits
@ -28,8 +30,13 @@ __switch_to:
SAVE_CALLEE_SAVED_KERNEL
/* Save the now KSP in task->thread.ksp */
st.as sp, [r0, (TASK_THREAD + THREAD_KSP)/4]
#if KSP_WORD_OFF <= 255
st.as sp, [r0, KSP_WORD_OFF]
#else
/* Workaround for NR_CPUS=4k as ST.as can only take s9 offset */
add2 r24, r0, KSP_WORD_OFF
st sp, [r24]
#endif
/*
* Return last task in r0 (return reg)
* On ARC, Return reg = First Arg reg = r0.