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[MIPS] Fix potential latency problem due to non-atomic cpu_wait.

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If an interrupt happened between checking of NEED_RESCHED and WAIT
instruction, adjust EPC to restart from checking of NEED_RESCHED.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Atsushi Nemoto 2007-11-12 02:05:18 +09:00 committed by Ralf Baechle
parent 6657fe0a02
commit c65a5480ff
3 changed files with 55 additions and 20 deletions
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16
arch/mips/kernel/cpu-probe.c
View file

@ -45,18 +45,7 @@ static void r39xx_wait(void)
local_irq_enable();
}
/*
* There is a race when WAIT instruction executed with interrupt
* enabled.
* But it is implementation-dependent wheter the pipelie restarts when
* a non-enabled interrupt is requested.
*/
static void r4k_wait(void)
{
__asm__(" .set mips3 \n"
" wait \n"
" .set mips0 \n");
}
extern void r4k_wait(void);
/*
* This variant is preferable as it allows testing need_resched and going to
@ -128,7 +117,7 @@ static int __init wait_disable(char *s)
__setup("nowait", wait_disable);
static inline void check_wait(void)
void __init check_wait(void)
{
struct cpuinfo_mips *c = &current_cpu_data;
@ -242,7 +231,6 @@ static inline void check_errata(void)
void __init check_bugs32(void)
{
check_wait();
check_errata();
}

37
arch/mips/kernel/genex.S
View file

@ -20,6 +20,7 @@
#include <asm/stackframe.h>
#include <asm/war.h>
#include <asm/page.h>
#include <asm/thread_info.h>
#define PANIC_PIC(msg) \
.set push; \
@ -126,7 +127,42 @@ handle_vcei:
__FINIT
.align 5 /* 32 byte rollback region */
LEAF(r4k_wait)
.set push
.set noreorder
/* start of rollback region */
LONG_L t0, TI_FLAGS($28)
nop
andi t0, _TIF_NEED_RESCHED
bnez t0, 1f
nop
nop
nop
.set mips3
wait
/* end of rollback region (the region size must be power of two) */
.set pop
1:
jr ra
END(r4k_wait)
.macro BUILD_ROLLBACK_PROLOGUE handler
FEXPORT(rollback_\handler)
.set push
.set noat
MFC0 k0, CP0_EPC
PTR_LA k1, r4k_wait
ori k0, 0x1f /* 32 byte rollback region */
xori k0, 0x1f
bne k0, k1, 9f
MTC0 k0, CP0_EPC
9:
.set pop
.endm
.align 5
BUILD_ROLLBACK_PROLOGUE handle_int
NESTED(handle_int, PT_SIZE, sp)
#ifdef CONFIG_TRACE_IRQFLAGS
/*
@ -201,6 +237,7 @@ NESTED(except_vec_ejtag_debug, 0, sp)
* This prototype is copied to ebase + n*IntCtl.VS and patched
* to invoke the handler
*/
BUILD_ROLLBACK_PROLOGUE except_vec_vi
NESTED(except_vec_vi, 0, sp)
SAVE_SOME
SAVE_AT

22
arch/mips/kernel/traps.c
View file

@ -46,6 +46,9 @@
#include <asm/types.h>
#include <asm/stacktrace.h>
extern void check_wait(void);
extern asmlinkage void r4k_wait(void);
extern asmlinkage void rollback_handle_int(void);
extern asmlinkage void handle_int(void);
extern asmlinkage void handle_tlbm(void);
extern asmlinkage void handle_tlbl(void);
@ -1251,6 +1254,9 @@ static void *set_vi_srs_handler(int n, vi_handler_t addr, int srs)
extern char except_vec_vi, except_vec_vi_lui;
extern char except_vec_vi_ori, except_vec_vi_end;
extern char rollback_except_vec_vi;
char *vec_start = (cpu_wait == r4k_wait) ?
&rollback_except_vec_vi : &except_vec_vi;
#ifdef CONFIG_MIPS_MT_SMTC
/*
* We need to provide the SMTC vectored interrupt handler
@ -1258,11 +1264,11 @@ static void *set_vi_srs_handler(int n, vi_handler_t addr, int srs)
* Status.IM bit to be masked before going there.
*/
extern char except_vec_vi_mori;
const int mori_offset = &except_vec_vi_mori - &except_vec_vi;
const int mori_offset = &except_vec_vi_mori - vec_start;
#endif /* CONFIG_MIPS_MT_SMTC */
const int handler_len = &except_vec_vi_end - &except_vec_vi;
const int lui_offset = &except_vec_vi_lui - &except_vec_vi;
const int ori_offset = &except_vec_vi_ori - &except_vec_vi;
const int handler_len = &except_vec_vi_end - vec_start;
const int lui_offset = &except_vec_vi_lui - vec_start;
const int ori_offset = &except_vec_vi_ori - vec_start;
if (handler_len > VECTORSPACING) {
/*
@ -1272,7 +1278,7 @@ static void *set_vi_srs_handler(int n, vi_handler_t addr, int srs)
panic("VECTORSPACING too small");
}
memcpy(b, &except_vec_vi, handler_len);
memcpy(b, vec_start, handler_len);
#ifdef CONFIG_MIPS_MT_SMTC
BUG_ON(n > 7); /* Vector index %d exceeds SMTC maximum. */
@ -1554,6 +1560,10 @@ void __init trap_init(void)
extern char except_vec3_generic, except_vec3_r4000;
extern char except_vec4;
unsigned long i;
int rollback;
check_wait();
rollback = (cpu_wait == r4k_wait);
#if defined(CONFIG_KGDB)
if (kgdb_early_setup)
@ -1618,7 +1628,7 @@ void __init trap_init(void)
if (board_be_init)
board_be_init();
set_except_vector(0, handle_int);
set_except_vector(0, rollback ? rollback_handle_int : handle_int);
set_except_vector(1, handle_tlbm);
set_except_vector(2, handle_tlbl);
set_except_vector(3, handle_tlbs);