That'll do it. My patch wasn't enough.
I added some sanity checks to get_wchan and it hit one while running
overnight.
The task being examined transitioned from !TASK_RUNNING to
TASK_RUNNING while it was being examined. Doh!
Definately not SMP/preempt safe as written today.
--
Dave Johnson
Starent Networks
Atsushi Nemoto writes:
> >>>>> On Thu, 30 Jun 2005 11:50:57 -0400, Dave Johnson
> >>>>> <djohnson+linuxmips@sw.starentnetworks.com> said:
> dave> The PC it was trying to lookup is in preempt_schedule_irq().
> dave> Without preempt_schedule_irq in mfinfo[] it ended up with the
> dave> wrong function and then dereferenced a NULL FP.
>
> dave> Should this be in mfinfo or am I on the wrong track here?
> ...
> dave> Also, __preempt_spin_lock and __preempt_write_lock are nowhere
> dave> to be found so I had to remove those from the table.
>
> Well, The current get_wchan implementation is still problematic
> because:
>
> * Some functions in __sched (and __lock) section are static.
> * Functions in __lock are not handled.
> * Maintenance of the struct mips_frame_info mfinfo[] is a pain.
> * sleep_on*() is deprecated. kernel-janitors people want to remove
> references for them.
>
> I suppose searching a caller of scheduling functions in get_wchan is
> not necessary. Calling thread_saved_pc() will be enough for most
> usage.
>
> So I posted a patch to simplify things a while ago.
>
> http://www.linux-mips.org/cgi-bin/mesg.cgi?a=linux-mips&i=20050126.120916.88699500.nemoto%40toshiba-tops.co.jp
>
> And here is a revised patch.
>
> diff -u linux-mips/arch/mips/kernel/process.c linux/arch/mips/kernel/process.c
> --- linux-mips/arch/mips/kernel/process.c 2005-06-21 17:34:10.000000000
> +0900
> +++ linux/arch/mips/kernel/process.c 2005-07-01 11:15:26.000000000 +0900
> @@ -270,47 +270,15 @@
> }
>
> static struct mips_frame_info {
> - void *func;
> - int omit_fp; /* compiled without fno-omit-frame-pointer */
> int frame_offset;
> int pc_offset;
> -} schedule_frame, mfinfo[] = {
> - { schedule, 0 }, /* must be first */
> - /* arch/mips/kernel/semaphore.c */
> - { __down, 1 },
> - { __down_interruptible, 1 },
> - /* kernel/sched.c */
> -#ifdef CONFIG_PREEMPT
> - { preempt_schedule, 0 },
> -#endif
> - { wait_for_completion, 0 },
> - { interruptible_sleep_on, 0 },
> - { interruptible_sleep_on_timeout, 0 },
> - { sleep_on, 0 },
> - { sleep_on_timeout, 0 },
> - { yield, 0 },
> - { io_schedule, 0 },
> - { io_schedule_timeout, 0 },
> -#if defined(CONFIG_SMP) && defined(CONFIG_PREEMPT)
> - { __preempt_spin_lock, 0 },
> - { __preempt_write_lock, 0 },
> -#endif
> - /* kernel/timer.c */
> - { schedule_timeout, 1 },
> -/* { nanosleep_restart, 1 }, */
> - /* lib/rwsem-spinlock.c */
> - { __down_read, 1 },
> - { __down_write, 1 },
> -};
> -
> -static int mips_frame_info_initialized;
> -static int __init get_frame_info(struct mips_frame_info *info)
> +} schedule_frame;
> +static int __init get_frame_info(struct mips_frame_info *info, void *func)
> {
> int i;
> - void *func = info->func;
> union mips_instruction *ip = (union mips_instruction *)func;
> info->pc_offset = -1;
> - info->frame_offset = info->omit_fp ? 0 : -1;
> + info->frame_offset = -1;
> for (i = 0; i < 128; i++, ip++) {
> /* if jal, jalr, jr, stop. */
> if (ip->j_format.opcode == jal_op ||
> @@ -358,26 +326,7 @@
>
> static int __init frame_info_init(void)
> {
> - int i, found;
> - for (i = 0; i < ARRAY_SIZE(mfinfo); i++)
> - if (get_frame_info(&mfinfo[i]))
> - return -1;
> - schedule_frame = mfinfo[0];
> - /* bubble sort */
> - do {
> - struct mips_frame_info tmp;
> - found = 0;
> - for (i = 1; i < ARRAY_SIZE(mfinfo); i++) {
> - if (mfinfo[i-1].func > mfinfo[i].func) {
> - tmp = mfinfo[i];
> - mfinfo[i] = mfinfo[i-1];
> - mfinfo[i-1] = tmp;
> - found = 1;
> - }
> - }
> - } while (found);
> - mips_frame_info_initialized = 1;
> - return 0;
> + return get_frame_info(&schedule_frame, schedule);
> }
>
> arch_initcall(frame_info_init);
> @@ -398,39 +347,12 @@
> return ((unsigned long *)t->reg29)[schedule_frame.pc_offset];
> }
>
> -/* get_wchan - a maintenance nightmare^W^Wpain in the ass ... */
> unsigned long get_wchan(struct task_struct *p)
> {
> - unsigned long frame, pc;
> -
> if (!p || p == current || p->state == TASK_RUNNING)
> return 0;
>
> - if (!mips_frame_info_initialized)
> - return 0;
> - pc = thread_saved_pc(p);
> -
> - if (!in_sched_functions(pc))
> - goto out;
> -
> - frame = ((unsigned long *)p->thread.reg30)[schedule_frame.frame_offset];
> - do {
> - int i;
> - for (i = ARRAY_SIZE(mfinfo) - 1; i >= 0; i--) {
> - if (pc >= (unsigned long) mfinfo[i].func)
> - break;
> - }
> - if (i < 0)
> - break;
> -
> - if (mfinfo[i].omit_fp)
> - break;
> - pc = ((unsigned long *)frame)[mfinfo[i].pc_offset];
> - frame = ((unsigned long *)frame)[mfinfo[i].frame_offset];
> - } while (in_sched_functions(pc));
> -
> -out:
> - return pc;
> + return thread_saved_pc(p);
> }
>
> EXPORT_SYMBOL(get_wchan);
>
>
> ---
> Atsushi Nemoto
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