Re: [PATCH v2] exit: dump thread info on global init exit

[chenqiwu <qiwuchen55@gmail.com>]

On Fri, Nov 10, 2023 at 11:20:43AM +0800, chenqiwu wrote:
> Currently, there are various global init exit issues encountered
> on Andriod/linux system. It's hard to debug these issues on product
> environment without a usable coredump, This patch dump the last
> exit thread executable sections and regs to find the exit reason
> before panic.
> 
> Signed-off-by: chenqiwu <qiwu.chen@transsion.com>
> Tested-by: chenqiwu <qiwu.chen@transsion.com>
> ---
>  kernel/exit.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 76 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/exit.c b/kernel/exit.c
> index ee9f43bed49a..af2e24bc3ecd 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -13,6 +13,7 @@
>  #include <linux/sched/task.h>
>  #include <linux/sched/task_stack.h>
>  #include <linux/sched/cputime.h>
> +#include <linux/sched/debug.h>
>  #include <linux/interrupt.h>
>  #include <linux/module.h>
>  #include <linux/capability.h>
> @@ -806,6 +807,76 @@ static void synchronize_group_exit(struct task_struct *tsk, long code)
>  	spin_unlock_irq(&sighand->siglock);
>  }
>  
> +/*
> + * This function only dump thread executable sections to reduce maps space,
> + * since an unhandled falut in user mode is likely generated from code section.
> + */
> +static void dump_thread_maps_info(struct task_struct *tsk)
> +{
> +	struct vm_area_struct *vma;
> +	struct mm_struct *mm = tsk->mm;
> +
> +	if (!mmap_read_trylock(mm))
> +		return;
> +
> +	VMA_ITERATOR(vmi, mm, 0);
> +	pr_info("%s-%d: Dump maps info start\n", tsk->comm, task_pid_nr(tsk));
> +	for_each_vma(vmi, vma) {
> +		struct file *file = vma->vm_file;
> +		int flags = vma->vm_flags;
> +		unsigned long long pgoff = ((loff_t)vma->vm_pgoff) << PAGE_SHIFT;
> +
> +		if (file) {
> +			if (flags & VM_EXEC) {
> +				char tpath[256] = {0};
> +				char *pathname = d_path(&file->f_path, tpath, sizeof(tpath));
> +
> +				pr_info("%08lx-%08lx %c%c%c%c %08llx %s\n",
> +					vma->vm_start, vma->vm_end,
> +					flags & VM_READ ? 'r' : '-',
> +					flags & VM_WRITE ? 'w' : '-',
> +					flags & VM_EXEC ? 'x' : '-',
> +					flags & VM_MAYSHARE ? 's' : 'p',
> +					pgoff, pathname);
> +			}
> +		} else {
> +			const char *name = arch_vma_name(vma);
> +
> +			if (!name) {
> +				struct mm_struct *mm = vma->vm_mm;
> +
> +				if (mm) {
> +					if (vma_is_initial_heap(vma))
> +						name = "[heap]";
> +					else if (vma_is_initial_stack(vma))
> +						name = "[stack]";
> +				} else {
> +					name = "[vdso]";
> +				}
> +			}
> +
> +			if (name && (flags & VM_EXEC)) {
> +				pr_info("%08lx-%08lx %c%c%c%c %08llx %s\n",
> +					vma->vm_start, vma->vm_end,
> +					flags & VM_READ ? 'r' : '-',
> +					flags & VM_WRITE ? 'w' : '-',
> +					flags & VM_EXEC ? 'x' : '-',
> +					flags & VM_MAYSHARE ? 's' : 'p', pgoff, name);
> +			}
> +		}
> +	}
> +	mmap_read_unlock(mm);
> +	pr_info("%s-%d: Dump maps info end\n", tsk->comm, task_pid_nr(tsk));
> +}
> +
> +static void dump_thread_info(struct task_struct *tsk)
> +{
> +	struct pt_regs *regs = task_pt_regs(tsk);
> +
> +	dump_thread_maps_info(tsk);
> +	show_regs(regs);
> +}
> +
>  void __noreturn do_exit(long code)
>  {
>  	struct task_struct *tsk = current;
> @@ -833,12 +904,14 @@ void __noreturn do_exit(long code)
>  	group_dead = atomic_dec_and_test(&tsk->signal->live);
>  	if (group_dead) {
>  		/*
> -		 * If the last thread of global init has exited, panic
> -		 * immediately to get a useable coredump.
> +		 * If the last thread of global init has exited, dump
> +		 * some usable information before panic.
>  		 */
> -		if (unlikely(is_global_init(tsk)))
> +		if (unlikely(is_global_init(tsk))) {
> +			dump_thread_info(tsk);
>  			panic("Attempted to kill init! exitcode=0x%08x\n",
>  				tsk->signal->group_exit_code ?: (int)code);
> +		}
>  
>  #ifdef CONFIG_POSIX_TIMERS
>  		hrtimer_cancel(&tsk->signal->real_timer);
> -- 
> 2.25.1
>

Add oleg for reviewer.