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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>
361 lines
8.4 KiB
C
361 lines
8.4 KiB
C
/*
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* File: arch/blackfin/kernel/process.c
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* Based on:
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* Author:
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*
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* Created:
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* Description: Blackfin architecture-dependent process handling.
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*
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* Modified:
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* Copyright 2004-2006 Analog Devices Inc.
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*
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* Bugs: Enter bugs at http://blackfin.uclinux.org/
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see the file COPYING, or write
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* to the Free Software Foundation, Inc.,
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* 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <linux/module.h>
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#include <linux/smp_lock.h>
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#include <linux/unistd.h>
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#include <linux/user.h>
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#include <linux/uaccess.h>
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#include <linux/sched.h>
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#include <linux/tick.h>
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#include <linux/fs.h>
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#include <linux/err.h>
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#include <asm/blackfin.h>
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#include <asm/fixed_code.h>
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asmlinkage void ret_from_fork(void);
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/* Points to the SDRAM backup memory for the stack that is currently in
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* L1 scratchpad memory.
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*/
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void *current_l1_stack_save;
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/* The number of tasks currently using a L1 stack area. The SRAM is
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* allocated/deallocated whenever this changes from/to zero.
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*/
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int nr_l1stack_tasks;
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/* Start and length of the area in L1 scratchpad memory which we've allocated
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* for process stacks.
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*/
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void *l1_stack_base;
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unsigned long l1_stack_len;
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/*
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* Powermanagement idle function, if any..
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*/
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void (*pm_idle)(void) = NULL;
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EXPORT_SYMBOL(pm_idle);
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void (*pm_power_off)(void) = NULL;
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EXPORT_SYMBOL(pm_power_off);
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/*
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* The idle loop on BFIN
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*/
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#ifdef CONFIG_IDLE_L1
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static void default_idle(void)__attribute__((l1_text));
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void cpu_idle(void)__attribute__((l1_text));
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#endif
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/*
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* This is our default idle handler. We need to disable
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* interrupts here to ensure we don't miss a wakeup call.
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*/
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static void default_idle(void)
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{
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local_irq_disable();
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if (!need_resched())
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idle_with_irq_disabled();
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local_irq_enable();
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}
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/*
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* The idle thread. We try to conserve power, while trying to keep
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* overall latency low. The architecture specific idle is passed
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* a value to indicate the level of "idleness" of the system.
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*/
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void cpu_idle(void)
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{
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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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#ifdef CONFIG_HOTPLUG_CPU
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if (cpu_is_offline(smp_processor_id()))
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cpu_die();
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#endif
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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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}
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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 * fpregs)
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{
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return 1;
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}
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/*
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* This gets run with P1 containing the
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* function to call, and R1 containing
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* the "args". Note P0 is clobbered on the way here.
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*/
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void kernel_thread_helper(void);
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__asm__(".section .text\n"
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".align 4\n"
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"_kernel_thread_helper:\n\t"
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"\tsp += -12;\n\t"
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"\tr0 = r1;\n\t" "\tcall (p1);\n\t" "\tcall _do_exit;\n" ".previous");
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/*
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* Create a kernel thread.
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*/
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pid_t 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.r1 = (unsigned long)arg;
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regs.p1 = (unsigned long)fn;
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regs.pc = (unsigned long)kernel_thread_helper;
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regs.orig_p0 = -1;
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/* Set bit 2 to tell ret_from_fork we should be returning to kernel
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mode. */
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regs.ipend = 0x8002;
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__asm__ __volatile__("%0 = syscfg;":"=da"(regs.syscfg):);
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return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, ®s, 0, NULL,
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NULL);
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}
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void flush_thread(void)
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{
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}
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asmlinkage int bfin_vfork(struct pt_regs *regs)
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{
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return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, rdusp(), regs, 0, NULL,
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NULL);
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}
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asmlinkage int bfin_clone(struct pt_regs *regs)
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{
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unsigned long clone_flags;
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unsigned long newsp;
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/* syscall2 puts clone_flags in r0 and usp in r1 */
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clone_flags = regs->r0;
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newsp = regs->r1;
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if (!newsp)
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newsp = rdusp();
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else
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newsp -= 12;
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return do_fork(clone_flags, newsp, regs, 0, NULL, NULL);
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}
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int
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copy_thread(int nr, unsigned long clone_flags,
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unsigned long usp, unsigned long topstk,
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struct task_struct *p, struct pt_regs *regs)
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{
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struct pt_regs *childregs;
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childregs = (struct pt_regs *) (task_stack_page(p) + THREAD_SIZE) - 1;
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*childregs = *regs;
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childregs->r0 = 0;
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p->thread.usp = usp;
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p->thread.ksp = (unsigned long)childregs;
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p->thread.pc = (unsigned long)ret_from_fork;
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return 0;
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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 *name, char __user * __user *argv, char __user * __user *envp)
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{
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int error;
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char *filename;
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struct pt_regs *regs = (struct pt_regs *)((&name) + 6);
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lock_kernel();
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filename = getname(name);
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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, argv, envp, regs);
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putname(filename);
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out:
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unlock_kernel();
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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 fp, pc;
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unsigned long stack_page;
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int count = 0;
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if (!p || p == current || p->state == TASK_RUNNING)
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return 0;
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stack_page = (unsigned long)p;
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fp = p->thread.usp;
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do {
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if (fp < stack_page + sizeof(struct thread_info) ||
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fp >= 8184 + stack_page)
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return 0;
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pc = ((unsigned long *)fp)[1];
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if (!in_sched_functions(pc))
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return pc;
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fp = *(unsigned long *)fp;
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}
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while (count++ < 16);
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return 0;
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}
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void finish_atomic_sections (struct pt_regs *regs)
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{
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int __user *up0 = (int __user *)regs->p0;
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if (regs->pc < ATOMIC_SEQS_START || regs->pc >= ATOMIC_SEQS_END)
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return;
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switch (regs->pc) {
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case ATOMIC_XCHG32 + 2:
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put_user(regs->r1, up0);
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regs->pc += 2;
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break;
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case ATOMIC_CAS32 + 2:
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case ATOMIC_CAS32 + 4:
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if (regs->r0 == regs->r1)
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put_user(regs->r2, up0);
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regs->pc = ATOMIC_CAS32 + 8;
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break;
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case ATOMIC_CAS32 + 6:
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put_user(regs->r2, up0);
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regs->pc += 2;
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break;
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case ATOMIC_ADD32 + 2:
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regs->r0 = regs->r1 + regs->r0;
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/* fall through */
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case ATOMIC_ADD32 + 4:
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put_user(regs->r0, up0);
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regs->pc = ATOMIC_ADD32 + 6;
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break;
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case ATOMIC_SUB32 + 2:
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regs->r0 = regs->r1 - regs->r0;
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/* fall through */
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case ATOMIC_SUB32 + 4:
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put_user(regs->r0, up0);
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regs->pc = ATOMIC_SUB32 + 6;
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break;
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case ATOMIC_IOR32 + 2:
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regs->r0 = regs->r1 | regs->r0;
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/* fall through */
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case ATOMIC_IOR32 + 4:
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put_user(regs->r0, up0);
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regs->pc = ATOMIC_IOR32 + 6;
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break;
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case ATOMIC_AND32 + 2:
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regs->r0 = regs->r1 & regs->r0;
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/* fall through */
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case ATOMIC_AND32 + 4:
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put_user(regs->r0, up0);
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regs->pc = ATOMIC_AND32 + 6;
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break;
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case ATOMIC_XOR32 + 2:
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regs->r0 = regs->r1 ^ regs->r0;
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/* fall through */
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case ATOMIC_XOR32 + 4:
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put_user(regs->r0, up0);
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regs->pc = ATOMIC_XOR32 + 6;
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break;
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}
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}
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#if defined(CONFIG_ACCESS_CHECK)
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/* Return 1 if access to memory range is OK, 0 otherwise */
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int _access_ok(unsigned long addr, unsigned long size)
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{
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if (size == 0)
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return 1;
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if (addr > (addr + size))
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return 0;
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if (segment_eq(get_fs(), KERNEL_DS))
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return 1;
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#ifdef CONFIG_MTD_UCLINUX
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if (addr >= memory_start && (addr + size) <= memory_end)
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return 1;
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if (addr >= memory_mtd_end && (addr + size) <= physical_mem_end)
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return 1;
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#ifdef CONFIG_ROMFS_MTD_FS
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/* For XIP, allow user space to use pointers within the ROMFS. */
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if (addr >= memory_mtd_start && (addr + size) <= memory_mtd_end)
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return 1;
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#endif
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#else
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if (addr >= memory_start && (addr + size) <= physical_mem_end)
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return 1;
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#endif
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if (addr >= (unsigned long)__init_begin &&
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addr + size <= (unsigned long)__init_end)
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return 1;
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if (addr >= L1_SCRATCH_START
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&& addr + size <= L1_SCRATCH_START + L1_SCRATCH_LENGTH)
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return 1;
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#if L1_CODE_LENGTH != 0
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if (addr >= L1_CODE_START + (_etext_l1 - _stext_l1)
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&& addr + size <= L1_CODE_START + L1_CODE_LENGTH)
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return 1;
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#endif
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#if L1_DATA_A_LENGTH != 0
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if (addr >= L1_DATA_A_START + (_ebss_l1 - _sdata_l1)
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&& addr + size <= L1_DATA_A_START + L1_DATA_A_LENGTH)
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return 1;
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#endif
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#if L1_DATA_B_LENGTH != 0
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if (addr >= L1_DATA_B_START
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&& addr + size <= L1_DATA_B_START + L1_DATA_B_LENGTH)
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return 1;
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#endif
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return 0;
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}
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EXPORT_SYMBOL(_access_ok);
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#endif /* CONFIG_ACCESS_CHECK */
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