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    Subject[patch v2 15/35] Hexagon: Add init_task and process functions
    Fixed potential race-to-sleep condition in cpu_idle().  I hope.

    If called with interrupts disabled, our __vmwait() actually just returns
    without servicing it. Let me know if there's any other condition that
    I've missed...


    Signed-off-by: Richard Kuo <rkuo@codeaurora.org>

    ---
    arch/hexagon/kernel/init_task.c | 54 +++++++
    arch/hexagon/kernel/process.c | 278 ++++++++++++++++++++++++++++++++++++++++
    2 files changed, 332 insertions(+)

    Index: linux-hexagon-kernel/arch/hexagon/kernel/init_task.c
    ===================================================================
    --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    +++ linux-hexagon-kernel/arch/hexagon/kernel/init_task.c 2011-08-24 18:45:48.203877165 -0500
    @@ -0,0 +1,54 @@
    +/*
    + * Init task definition
    + *
    + * Copyright (c) 2010-2011, Code Aurora Forum. All rights reserved.
    + *
    + * This program is free software; you can redistribute it and/or modify
    + * it under the terms of the GNU General Public License version 2 and
    + * only version 2 as published by the Free Software Foundation.
    + *
    + * This program is distributed in the hope that it will be useful,
    + * but WITHOUT ANY WARRANTY; without even the implied warranty of
    + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    + * GNU General Public License for more details.
    + *
    + * You should have received a copy of the GNU General Public License
    + * along with this program; if not, write to the Free Software
    + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
    + * 02110-1301, USA.
    + */
    +
    +#include <linux/mm.h>
    +#include <linux/module.h>
    +#include <linux/sched.h>
    +#include <linux/init_task.h>
    +#include <linux/fs.h>
    +#include <linux/mqueue.h>
    +#include <asm/thread_info.h>
    +#include <asm/uaccess.h>
    +#include <asm/pgtable.h>
    +
    +static struct signal_struct init_signals = INIT_SIGNALS(init_signals);
    +static struct sighand_struct init_sighand = INIT_SIGHAND(init_sighand);
    +
    +/*
    + * Initial thread structure.
    + *
    + * We need to make sure that this is 8192-byte aligned due to the
    + * way process stacks are handled. This is done by making sure
    + * the linker maps this in the .text segment right after head.S,
    + * and making head.S ensure the proper alignment.
    + */
    +union thread_union init_thread_union
    + __attribute__((__section__(".data.init_task"),
    + __aligned__(THREAD_SIZE))) = {
    + INIT_THREAD_INFO(init_task)
    + };
    +
    +/*
    + * Initial task structure.
    + *
    + * All other task structs will be allocated on slabs in fork.c
    + */
    +struct task_struct init_task = INIT_TASK(init_task);
    +EXPORT_SYMBOL(init_task);
    Index: linux-hexagon-kernel/arch/hexagon/kernel/process.c
    ===================================================================
    --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    +++ linux-hexagon-kernel/arch/hexagon/kernel/process.c 2011-08-24 18:45:48.203877165 -0500
    @@ -0,0 +1,278 @@
    +/*
    + * Process creation support for Hexagon
    + *
    + * Copyright (c) 2010-2011, Code Aurora Forum. All rights reserved.
    + *
    + * This program is free software; you can redistribute it and/or modify
    + * it under the terms of the GNU General Public License version 2 and
    + * only version 2 as published by the Free Software Foundation.
    + *
    + * This program is distributed in the hope that it will be useful,
    + * but WITHOUT ANY WARRANTY; without even the implied warranty of
    + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    + * GNU General Public License for more details.
    + *
    + * You should have received a copy of the GNU General Public License
    + * along with this program; if not, write to the Free Software
    + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
    + * 02110-1301, USA.
    + */
    +
    +#include <linux/sched.h>
    +#include <linux/types.h>
    +#include <linux/module.h>
    +#include <linux/tick.h>
    +#include <linux/uaccess.h>
    +#include <linux/slab.h>
    +
    +/*
    + * Kernel thread creation. The desired kernel function is "wrapped"
    + * in the kernel_thread_helper function, which does cleanup
    + * afterwards.
    + */
    +static void __noreturn kernel_thread_helper(void *arg, int (*fn)(void *))
    +{
    + do_exit(fn(arg));
    +}
    +
    +int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
    +{
    + struct pt_regs regs;
    +
    + memset(&regs, 0, sizeof(regs));
    + /*
    + * Yes, we're exploting illicit knowledge of the ABI here.
    + */
    + regs.r00 = (unsigned long) arg;
    + regs.r01 = (unsigned long) fn;
    + pt_set_elr(&regs, (unsigned long)kernel_thread_helper);
    + pt_set_kmode(&regs);
    +
    + return do_fork(flags|CLONE_VM|CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
    +}
    +EXPORT_SYMBOL(kernel_thread);
    +
    +/*
    + * Program thread launch. Often defined as a macro in processor.h,
    + * but we're shooting for a small footprint and it's not an inner-loop
    + * performance-critical operation.
    + *
    + * The Hexagon ABI specifies that R28 is zero'ed before program launch,
    + * so that gets automatically done here. If we ever stop doing that here,
    + * we'll probably want to define the ELF_PLAT_INIT macro.
    + */
    +void start_thread(struct pt_regs *regs, unsigned long pc, unsigned long sp)
    +{
    + /* Set to run with user-mode data segmentation */
    + set_fs(USER_DS);
    + /* We want to zero all data-containing registers. Is this overkill? */
    + memset(regs, 0, sizeof(*regs));
    + /* We might want to also zero all Processor registers here */
    + pt_set_usermode(regs);
    + pt_set_elr(regs, pc);
    + pt_set_rte_sp(regs, sp);
    +}
    +
    +/*
    + * Spin, or better still, do a hardware or VM wait instruction
    + * If hardware or VM offer wait termination even though interrupts
    + * are disabled.
    + */
    +static void default_idle(void)
    +{
    + __vmwait();
    +}
    +
    +void (*idle_sleep)(void) = default_idle;
    +
    +void cpu_idle(void)
    +{
    + while (1) {
    + tick_nohz_stop_sched_tick(1);
    + local_irq_disable();
    + while (!need_resched()) {
    + idle_sleep();
    + /* interrupts wake us up, but aren't serviced */
    + local_irq_enable(); /* service interrupt */
    + local_irq_disable();
    + }
    + tick_nohz_restart_sched_tick();
    + schedule();
    + }
    +}
    +
    +/*
    + * Return saved PC of a blocked thread
    + */
    +unsigned long thread_saved_pc(struct task_struct *tsk)
    +{
    + return 0;
    +}
    +
    +/*
    + * Copy architecture-specific thread state
    + */
    +int copy_thread(unsigned long clone_flags, unsigned long usp,
    + unsigned long unused, struct task_struct *p,
    + struct pt_regs *regs)
    +{
    + struct thread_info *ti = task_thread_info(p);
    + struct hexagon_switch_stack *ss;
    + struct pt_regs *childregs;
    + asmlinkage void ret_from_fork(void);
    +
    + childregs = (struct pt_regs *) (((unsigned long) ti + THREAD_SIZE) -
    + sizeof(*childregs));
    +
    + memcpy(childregs, regs, sizeof(*childregs));
    + ti->regs = childregs;
    +
    + /*
    + * Establish kernel stack pointer and initial PC for new thread
    + */
    + ss = (struct hexagon_switch_stack *) ((unsigned long) childregs -
    + sizeof(*ss));
    + ss->lr = (unsigned long)ret_from_fork;
    + p->thread.switch_sp = ss;
    +
    + /* If User mode thread, set pt_reg stack pointer as per parameter */
    + if (user_mode(childregs)) {
    + pt_set_rte_sp(childregs, usp);
    +
    + /* Child sees zero return value */
    + childregs->r00 = 0;
    +
    + /*
    + * The clone syscall has the C signature:
    + * int [r0] clone(int flags [r0],
    + * void *child_frame [r1],
    + * void *parent_tid [r2],
    + * void *child_tid [r3],
    + * void *thread_control_block [r4]);
    + * ugp is used to provide TLS support.
    + */
    + if (clone_flags & CLONE_SETTLS)
    + childregs->ugp = childregs->r04;
    +
    + /*
    + * Parent sees new pid -- not necessary, not even possible at
    + * this point in the fork process
    + * Might also want to set things like ti->addr_limit
    + */
    + } else {
    + /*
    + * If kernel thread, resume stack is kernel stack base.
    + * Note that this is pointer arithmetic on pt_regs *
    + */
    + pt_set_rte_sp(childregs, (unsigned long)(childregs + 1));
    + /*
    + * We need the current thread_info fast path pointer
    + * set up in pt_regs. The register to be used is
    + * parametric for assembler code, but the mechanism
    + * doesn't drop neatly into C. Needs to be fixed.
    + */
    + childregs->THREADINFO_REG = (unsigned long) ti;
    + }
    +
    + /*
    + * thread_info pointer is pulled out of task_struct "stack"
    + * field on switch_to.
    + */
    + p->stack = (void *)ti;
    +
    + return 0;
    +}
    +
    +/*
    + * Release any architecture-specific resources locked by thread
    + */
    +void release_thread(struct task_struct *dead_task)
    +{
    +}
    +
    +/*
    + * Free any architecture-specific thread data structures, etc.
    + */
    +void exit_thread(void)
    +{
    +}
    +
    +/*
    + * Some archs flush debug and FPU info here
    + */
    +void flush_thread(void)
    +{
    +}
    +
    +/*
    + * The "wait channel" terminology is archaic, but what we want
    + * is an identification of the point at which the scheduler
    + * was invoked by a blocked thread.
    + */
    +unsigned long get_wchan(struct task_struct *p)
    +{
    + unsigned long fp, pc;
    + unsigned long stack_page;
    + int count = 0;
    + if (!p || p == current || p->state == TASK_RUNNING)
    + return 0;
    +
    + stack_page = (unsigned long)task_stack_page(p);
    + fp = ((struct hexagon_switch_stack *)p->thread.switch_sp)->fp;
    + do {
    + if (fp < (stack_page + sizeof(struct thread_info)) ||
    + fp >= (THREAD_SIZE - 8 + stack_page))
    + return 0;
    + pc = ((unsigned long *)fp)[1];
    + if (!in_sched_functions(pc))
    + return pc;
    + fp = *(unsigned long *) fp;
    + } while (count++ < 16);
    +
    + return 0;
    +}
    +
    +/*
    + * Borrowed from PowerPC -- basically allow smaller kernel stacks if we
    + * go crazy with the page sizes.
    + */
    +#if THREAD_SHIFT < PAGE_SHIFT
    +
    +static struct kmem_cache *thread_info_cache;
    +
    +struct thread_info *alloc_thread_info_node(struct task_struct *tsk, int node)
    +{
    + struct thread_info *ti;
    +
    + ti = kmem_cache_alloc_node(thread_info_cache, GFP_KERNEL, node);
    + if (unlikely(ti == NULL))
    + return NULL;
    +#ifdef CONFIG_DEBUG_STACK_USAGE
    + memset(ti, 0, THREAD_SIZE);
    +#endif
    + return ti;
    +}
    +
    +void free_thread_info(struct thread_info *ti)
    +{
    + kmem_cache_free(thread_info_cache, ti);
    +}
    +
    +/* Weak symbol; called by init/main.c */
    +
    +void thread_info_cache_init(void)
    +{
    + thread_info_cache = kmem_cache_create("thread_info", THREAD_SIZE,
    + THREAD_SIZE, 0, NULL);
    + BUG_ON(thread_info_cache == NULL);
    +}
    +
    +#endif /* THREAD_SHIFT < PAGE_SHIFT */
    +
    +/*
    + * Required placeholder.
    + */
    +int dump_fpu(struct pt_regs *regs, elf_fpregset_t *fpu)
    +{
    + return 0;
    +}
    --

    Sent by an employee of the Qualcomm Innovation Center, Inc.
    The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.



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