b8f8c3cf0a
Jack Ren and Eric Miao tracked down the following long standing
problem in the NOHZ code:
scheduler switch to idle task
enable interrupts
Window starts here
----> interrupt happens (does not set NEED_RESCHED)
irq_exit() stops the tick
----> interrupt happens (does set NEED_RESCHED)
return from schedule()
cpu_idle(): preempt_disable();
Window ends here
The interrupts can happen at any point inside the race window. The
first interrupt stops the tick, the second one causes the scheduler to
rerun and switch away from idle again and we end up with the tick
disabled.
The fact that it needs two interrupts where the first one does not set
NEED_RESCHED and the second one does made the bug obscure and extremly
hard to reproduce and analyse. Kudos to Jack and Eric.
Solution: Limit the NOHZ functionality to the idle loop to make sure
that we can not run into such a situation ever again.
cpu_idle()
{
preempt_disable();
while(1) {
tick_nohz_stop_sched_tick(1); <- tell NOHZ code that we
are in the idle loop
while (!need_resched())
halt();
tick_nohz_restart_sched_tick(); <- disables NOHZ mode
preempt_enable_no_resched();
schedule();
preempt_disable();
}
}
In hindsight we should have done this forever, but ...
/me grabs a large brown paperbag.
Debugged-by: Jack Ren <jack.ren@marvell.com>,
Debugged-by: eric miao <eric.y.miao@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
467 lines
10 KiB
C
467 lines
10 KiB
C
/*
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* arch/sh/kernel/process.c
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*
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* This file handles the architecture-dependent parts of process handling..
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*
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* Copyright (C) 1995 Linus Torvalds
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*
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* SuperH version: Copyright (C) 1999, 2000 Niibe Yutaka & Kaz Kojima
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* Copyright (C) 2006 Lineo Solutions Inc. support SH4A UBC
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* Copyright (C) 2002 - 2007 Paul Mundt
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*/
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#include <linux/module.h>
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#include <linux/mm.h>
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#include <linux/elfcore.h>
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#include <linux/pm.h>
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#include <linux/kallsyms.h>
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#include <linux/kexec.h>
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#include <linux/kdebug.h>
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#include <linux/tick.h>
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#include <linux/reboot.h>
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#include <linux/fs.h>
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#include <linux/preempt.h>
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#include <asm/uaccess.h>
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#include <asm/mmu_context.h>
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#include <asm/pgalloc.h>
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#include <asm/system.h>
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#include <asm/ubc.h>
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#include <asm/fpu.h>
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static int hlt_counter;
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int ubc_usercnt = 0;
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void (*pm_idle)(void);
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void (*pm_power_off)(void);
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EXPORT_SYMBOL(pm_power_off);
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void disable_hlt(void)
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{
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hlt_counter++;
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}
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EXPORT_SYMBOL(disable_hlt);
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void enable_hlt(void)
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{
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hlt_counter--;
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}
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EXPORT_SYMBOL(enable_hlt);
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static int __init nohlt_setup(char *__unused)
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{
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hlt_counter = 1;
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return 1;
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}
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__setup("nohlt", nohlt_setup);
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static int __init hlt_setup(char *__unused)
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{
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hlt_counter = 0;
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return 1;
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}
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__setup("hlt", hlt_setup);
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void default_idle(void)
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{
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if (!hlt_counter) {
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clear_thread_flag(TIF_POLLING_NRFLAG);
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smp_mb__after_clear_bit();
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set_bl_bit();
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while (!need_resched())
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cpu_sleep();
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clear_bl_bit();
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set_thread_flag(TIF_POLLING_NRFLAG);
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} else
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while (!need_resched())
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cpu_relax();
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}
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void cpu_idle(void)
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{
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set_thread_flag(TIF_POLLING_NRFLAG);
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/* endless idle loop with no priority at all */
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while (1) {
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void (*idle)(void) = pm_idle;
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if (!idle)
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idle = default_idle;
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tick_nohz_stop_sched_tick(1);
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while (!need_resched())
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idle();
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tick_nohz_restart_sched_tick();
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preempt_enable_no_resched();
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schedule();
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preempt_disable();
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check_pgt_cache();
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}
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}
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void machine_restart(char * __unused)
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{
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/* SR.BL=1 and invoke address error to let CPU reset (manual reset) */
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asm volatile("ldc %0, sr\n\t"
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"mov.l @%1, %0" : : "r" (0x10000000), "r" (0x80000001));
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}
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void machine_halt(void)
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{
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local_irq_disable();
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while (1)
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cpu_sleep();
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}
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void machine_power_off(void)
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{
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if (pm_power_off)
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pm_power_off();
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}
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void show_regs(struct pt_regs * regs)
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{
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printk("\n");
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printk("Pid : %d, Comm: %20s\n", task_pid_nr(current), current->comm);
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print_symbol("PC is at %s\n", instruction_pointer(regs));
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printk("PC : %08lx SP : %08lx SR : %08lx ",
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regs->pc, regs->regs[15], regs->sr);
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#ifdef CONFIG_MMU
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printk("TEA : %08x ", ctrl_inl(MMU_TEA));
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#else
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printk(" ");
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#endif
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printk("%s\n", print_tainted());
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printk("R0 : %08lx R1 : %08lx R2 : %08lx R3 : %08lx\n",
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regs->regs[0],regs->regs[1],
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regs->regs[2],regs->regs[3]);
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printk("R4 : %08lx R5 : %08lx R6 : %08lx R7 : %08lx\n",
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regs->regs[4],regs->regs[5],
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regs->regs[6],regs->regs[7]);
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printk("R8 : %08lx R9 : %08lx R10 : %08lx R11 : %08lx\n",
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regs->regs[8],regs->regs[9],
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regs->regs[10],regs->regs[11]);
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printk("R12 : %08lx R13 : %08lx R14 : %08lx\n",
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regs->regs[12],regs->regs[13],
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regs->regs[14]);
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printk("MACH: %08lx MACL: %08lx GBR : %08lx PR : %08lx\n",
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regs->mach, regs->macl, regs->gbr, regs->pr);
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show_trace(NULL, (unsigned long *)regs->regs[15], regs);
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}
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/*
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* Create a kernel thread
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*/
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/*
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* This is the mechanism for creating a new kernel thread.
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*
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*/
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extern void kernel_thread_helper(void);
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__asm__(".align 5\n"
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"kernel_thread_helper:\n\t"
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"jsr @r5\n\t"
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" nop\n\t"
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"mov.l 1f, r1\n\t"
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"jsr @r1\n\t"
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" mov r0, r4\n\t"
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".align 2\n\t"
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"1:.long do_exit");
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/* Don't use this in BL=1(cli). Or else, CPU resets! */
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int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
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{
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struct pt_regs regs;
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memset(®s, 0, sizeof(regs));
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regs.regs[4] = (unsigned long)arg;
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regs.regs[5] = (unsigned long)fn;
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regs.pc = (unsigned long)kernel_thread_helper;
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regs.sr = (1 << 30);
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/* Ok, create the new process.. */
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return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0,
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®s, 0, NULL, NULL);
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}
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/*
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* Free current thread data structures etc..
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*/
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void exit_thread(void)
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{
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if (current->thread.ubc_pc) {
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current->thread.ubc_pc = 0;
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ubc_usercnt -= 1;
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}
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}
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void flush_thread(void)
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{
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#if defined(CONFIG_SH_FPU)
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struct task_struct *tsk = current;
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/* Forget lazy FPU state */
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clear_fpu(tsk, task_pt_regs(tsk));
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clear_used_math();
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#endif
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}
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void release_thread(struct task_struct *dead_task)
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{
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/* do nothing */
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}
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/* Fill in the fpu structure for a core dump.. */
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int dump_fpu(struct pt_regs *regs, elf_fpregset_t *fpu)
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{
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int fpvalid = 0;
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#if defined(CONFIG_SH_FPU)
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struct task_struct *tsk = current;
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fpvalid = !!tsk_used_math(tsk);
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if (fpvalid) {
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unlazy_fpu(tsk, regs);
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memcpy(fpu, &tsk->thread.fpu.hard, sizeof(*fpu));
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}
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#endif
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return fpvalid;
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}
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asmlinkage void ret_from_fork(void);
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int copy_thread(int nr, unsigned long clone_flags, unsigned long usp,
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unsigned long unused,
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struct task_struct *p, struct pt_regs *regs)
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{
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struct thread_info *ti = task_thread_info(p);
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struct pt_regs *childregs;
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#if defined(CONFIG_SH_FPU)
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struct task_struct *tsk = current;
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unlazy_fpu(tsk, regs);
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p->thread.fpu = tsk->thread.fpu;
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copy_to_stopped_child_used_math(p);
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#endif
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childregs = task_pt_regs(p);
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*childregs = *regs;
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if (user_mode(regs)) {
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childregs->regs[15] = usp;
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ti->addr_limit = USER_DS;
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} else {
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childregs->regs[15] = (unsigned long)childregs;
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ti->addr_limit = KERNEL_DS;
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}
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if (clone_flags & CLONE_SETTLS)
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childregs->gbr = childregs->regs[0];
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childregs->regs[0] = 0; /* Set return value for child */
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p->thread.sp = (unsigned long) childregs;
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p->thread.pc = (unsigned long) ret_from_fork;
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p->thread.ubc_pc = 0;
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return 0;
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}
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/* Tracing by user break controller. */
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static void ubc_set_tracing(int asid, unsigned long pc)
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{
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#if defined(CONFIG_CPU_SH4A)
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unsigned long val;
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val = (UBC_CBR_ID_INST | UBC_CBR_RW_READ | UBC_CBR_CE);
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val |= (UBC_CBR_AIE | UBC_CBR_AIV_SET(asid));
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ctrl_outl(val, UBC_CBR0);
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ctrl_outl(pc, UBC_CAR0);
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ctrl_outl(0x0, UBC_CAMR0);
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ctrl_outl(0x0, UBC_CBCR);
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val = (UBC_CRR_RES | UBC_CRR_PCB | UBC_CRR_BIE);
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ctrl_outl(val, UBC_CRR0);
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/* Read UBC register that we wrote last, for checking update */
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val = ctrl_inl(UBC_CRR0);
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#else /* CONFIG_CPU_SH4A */
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ctrl_outl(pc, UBC_BARA);
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#ifdef CONFIG_MMU
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ctrl_outb(asid, UBC_BASRA);
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#endif
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ctrl_outl(0, UBC_BAMRA);
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if (current_cpu_data.type == CPU_SH7729 ||
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current_cpu_data.type == CPU_SH7710 ||
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current_cpu_data.type == CPU_SH7712) {
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ctrl_outw(BBR_INST | BBR_READ | BBR_CPU, UBC_BBRA);
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ctrl_outl(BRCR_PCBA | BRCR_PCTE, UBC_BRCR);
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} else {
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ctrl_outw(BBR_INST | BBR_READ, UBC_BBRA);
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ctrl_outw(BRCR_PCBA, UBC_BRCR);
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}
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#endif /* CONFIG_CPU_SH4A */
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}
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/*
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* switch_to(x,y) should switch tasks from x to y.
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*
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*/
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struct task_struct *__switch_to(struct task_struct *prev,
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struct task_struct *next)
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{
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#if defined(CONFIG_SH_FPU)
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unlazy_fpu(prev, task_pt_regs(prev));
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#endif
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#ifdef CONFIG_MMU
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/*
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* Restore the kernel mode register
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* k7 (r7_bank1)
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*/
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asm volatile("ldc %0, r7_bank"
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: /* no output */
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: "r" (task_thread_info(next)));
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#endif
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/* If no tasks are using the UBC, we're done */
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if (ubc_usercnt == 0)
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/* If no tasks are using the UBC, we're done */;
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else if (next->thread.ubc_pc && next->mm) {
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int asid = 0;
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#ifdef CONFIG_MMU
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asid |= cpu_asid(smp_processor_id(), next->mm);
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#endif
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ubc_set_tracing(asid, next->thread.ubc_pc);
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} else {
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#if defined(CONFIG_CPU_SH4A)
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ctrl_outl(UBC_CBR_INIT, UBC_CBR0);
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ctrl_outl(UBC_CRR_INIT, UBC_CRR0);
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#else
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ctrl_outw(0, UBC_BBRA);
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ctrl_outw(0, UBC_BBRB);
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#endif
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}
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return prev;
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}
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asmlinkage int sys_fork(unsigned long r4, unsigned long r5,
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unsigned long r6, unsigned long r7,
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struct pt_regs __regs)
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{
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#ifdef CONFIG_MMU
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struct pt_regs *regs = RELOC_HIDE(&__regs, 0);
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return do_fork(SIGCHLD, regs->regs[15], regs, 0, NULL, NULL);
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#else
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/* fork almost works, enough to trick you into looking elsewhere :-( */
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return -EINVAL;
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#endif
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}
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asmlinkage int sys_clone(unsigned long clone_flags, unsigned long newsp,
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unsigned long parent_tidptr,
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unsigned long child_tidptr,
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struct pt_regs __regs)
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{
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struct pt_regs *regs = RELOC_HIDE(&__regs, 0);
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if (!newsp)
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newsp = regs->regs[15];
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return do_fork(clone_flags, newsp, regs, 0,
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(int __user *)parent_tidptr,
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(int __user *)child_tidptr);
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}
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/*
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* This is trivial, and on the face of it looks like it
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* could equally well be done in user mode.
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*
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* Not so, for quite unobvious reasons - register pressure.
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* In user mode vfork() cannot have a stack frame, and if
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* done by calling the "clone()" system call directly, you
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* do not have enough call-clobbered registers to hold all
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* the information you need.
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*/
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asmlinkage int sys_vfork(unsigned long r4, unsigned long r5,
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unsigned long r6, unsigned long r7,
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struct pt_regs __regs)
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{
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struct pt_regs *regs = RELOC_HIDE(&__regs, 0);
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return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, regs->regs[15], regs,
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0, NULL, NULL);
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}
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/*
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* sys_execve() executes a new program.
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*/
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asmlinkage int sys_execve(char __user *ufilename, char __user * __user *uargv,
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char __user * __user *uenvp, unsigned long r7,
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struct pt_regs __regs)
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{
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struct pt_regs *regs = RELOC_HIDE(&__regs, 0);
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int error;
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char *filename;
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filename = getname(ufilename);
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error = PTR_ERR(filename);
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if (IS_ERR(filename))
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goto out;
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error = do_execve(filename, uargv, uenvp, regs);
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if (error == 0) {
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task_lock(current);
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current->ptrace &= ~PT_DTRACE;
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task_unlock(current);
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}
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putname(filename);
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out:
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return error;
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}
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unsigned long get_wchan(struct task_struct *p)
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{
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unsigned long pc;
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if (!p || p == current || p->state == TASK_RUNNING)
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return 0;
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/*
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* The same comment as on the Alpha applies here, too ...
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*/
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pc = thread_saved_pc(p);
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#ifdef CONFIG_FRAME_POINTER
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if (in_sched_functions(pc)) {
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unsigned long schedule_frame = (unsigned long)p->thread.sp;
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return ((unsigned long *)schedule_frame)[21];
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}
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#endif
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return pc;
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}
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asmlinkage void break_point_trap(void)
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{
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/* Clear tracing. */
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#if defined(CONFIG_CPU_SH4A)
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ctrl_outl(UBC_CBR_INIT, UBC_CBR0);
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ctrl_outl(UBC_CRR_INIT, UBC_CRR0);
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#else
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ctrl_outw(0, UBC_BBRA);
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ctrl_outw(0, UBC_BBRB);
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#endif
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current->thread.ubc_pc = 0;
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ubc_usercnt -= 1;
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force_sig(SIGTRAP, current);
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}
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