[Crash-utility] [RFC][PATCH]: crash aborts with cannot determine idle task

[Dave Anderson]

----- "Chandru" <chandru at in.ibm.com> wrote:

> Hi Dave,
> 
> Thanks a lot for catching the segfault issue and finding the root cause for it. Here
> follows the updated patch taking in the suggestions from the review comments.
> 
> kdump installs NT_PRSTATUS notes into vmcore file only to the cpus that were
> online at the time of crash. In such cases, while reading in the notes from the
> dump file, we are unsure of the cpu to NT_PRSTATUS  mapping. The cpu 
> possible, present and online map is not available until cpu_maps_init() initializes
> them. Hence we remap the prstatus pointer array to online cpus just after
> a call to this function. 
> 
> Signed-off-by: Chandru Siddalingappa <chandru at linux.vnet.ibm.com>
> Reviewed-by: Dave Anderson <anderson at redhat.com>
> Cc: Haren Myneni <haren at us.ibm.com>
> ---

This looks one good.  The only change that I will make is
in the map_cpu_prstatus() function -- which should just return
immediately if get_cpus_online() is equal to nd->num_prstatus_notes.

Thanks,
  Dave


>  
> --- crash-4.0-8.10/ppc64.c.orig	2009-06-08 16:08:09.000000000 +0530
> +++ crash-4.0-8.10/ppc64.c	2009-06-09 15:45:39.000000000 +0530
> @@ -2407,13 +2407,16 @@ ppc64_paca_init(void)
>  	if (!symbol_exists("paca"))
>  		error(FATAL, "PPC64: Could not find 'paca' symbol\n");
>  
> -	if (cpu_map_addr("present"))
> +	if (cpu_map_addr("possible"))
> +		map = POSSIBLE;
> +	else if (cpu_map_addr("present"))
>  		map = PRESENT;
>  	else if (cpu_map_addr("online"))
>  		map = ONLINE;
>  	else
> -		error(FATAL, 
> -		    "PPC64: cannot find 'cpu_present_map' or 'cpu_online_map'
> symbols\n");
> +		error(FATAL,
> +			"PPC64: cannot find 'cpu_possible_map' or\
> +			'cpu_present_map' or 'cpu_online_map' symbols\n");
>  
>  	if (!MEMBER_EXISTS("paca_struct", "data_offset"))
>  		return;
> @@ -2423,8 +2426,8 @@ ppc64_paca_init(void)
>  
>  	cpu_paca_buf = GETBUF(SIZE(ppc64_paca));
>  
> -	if (!(nr_paca = get_array_length("paca", NULL, 0))) 
> -		nr_paca = NR_CPUS;
> +	if (!(nr_paca = get_array_length("paca", NULL, 0)))
> +		nr_paca = (kt->kernel_NR_CPUS ? kt->kernel_NR_CPUS : NR_CPUS);
>  
>  	if (nr_paca > NR_CPUS) {
>  		error(WARNING, 
> @@ -2435,7 +2438,7 @@ ppc64_paca_init(void)
>  	
>  	for (i = cpus = 0; i < nr_paca; i++) {
>  		/*
> -		 * CPU present (or online)?
> +		 * CPU present or online or can exist in the system(possible)?
>  		 */
>  		if (!in_cpu_map(map, i))
>  			continue;
> --- crash-4.0-8.10/kernel.c.orig	2009-06-08 16:07:53.000000000 +0530
> +++ crash-4.0-8.10/kernel.c	2009-06-09 15:01:51.000000000 +0530
> @@ -74,6 +74,9 @@ kernel_init()
>  
>  	cpu_maps_init();
>  
> +	if (KDUMP_DUMPFILE())
> +		map_cpu_prstatus();
> +
>  	kt->stext = symbol_value("_stext");
>  	kt->etext = symbol_value("_etext");
>  	get_text_init_space(); 
> --- crash-4.0-8.10/netdump.c.orig	2009-06-08 16:07:58.000000000 +0530
> +++ crash-4.0-8.10/netdump.c	2009-06-09 16:24:52.000000000 +0530
> @@ -45,6 +45,38 @@ static void check_dumpfile_size(char *);
>  	(machine_type("IA64") || machine_type("PPC64"))
>  
>  /*
> + * kdump installs NT_PRSTATUS elf notes only to the cpus
> + * that were online during dumping. Hence we call into
> + * this function after reading the cpu map from the kernel,
> + * to remap the NT_PRSTATUS notes only to the online cpus
> + */
> +void map_cpu_prstatus(void)
> +{
> +	void *nt_ptr;
> +	int i, j, nrcpus;
> +
> +	/* temporary buffer to hold the prstatus_percpu array */
> +	if ((nt_ptr = (void *)calloc(nd->num_prstatus_notes,
> +				sizeof(void *))) == NULL)
> +		error(FATAL,
> +		   "cannot allocate a buffer to hold prstatus_percpu array\n");
> +
> +	memcpy((void *)nt_ptr, nd->nt_prstatus_percpu,
> +		(nd->num_prstatus_notes * sizeof(void *)));
> +	memset(nd->nt_prstatus_percpu, 0,
> +		(nd->num_prstatus_notes * sizeof(void *)));
> +
> +	nrcpus = (kt->kernel_NR_CPUS ? kt->kernel_NR_CPUS : NR_CPUS);
> +
> +	/* re-populate the array with the notes mapping to online cpus */
> +	for (i = 0, j = 0; i < nrcpus; i++)
> +		if (in_cpu_map(ONLINE, i))
> +			((unsigned long *)nd->nt_prstatus_percpu)[i] =
> +				((unsigned long *)nt_ptr)[j++];
> +	free(nt_ptr);
> +}
> +
> +/*
>   *  Determine whether a file is a netdump/diskdump/kdump creation, 
>   *  and if TRUE, initialize the vmcore_data structure.
>   */
> @@ -618,7 +650,7 @@ get_netdump_panic_task(void)
>  		crashing_cpu = -1;
>  		if (kernel_symbol_exists("crashing_cpu")) {
>  			get_symbol_data("crashing_cpu", sizeof(int), &i);
> -			if ((i >= 0) && (i < nd->num_prstatus_notes)) {
> +			if ((i >= 0) && in_cpu_map(ONLINE, i)) {
>  				crashing_cpu = i;
>  				if (CRASHDEBUG(1))
>  					error(INFO, 
> @@ -2236,7 +2268,7 @@ get_netdump_regs_ppc64(struct bt_info *b
>  		 * CPUs if they responded to an IPI.
>  		 */
>                  if (nd->num_prstatus_notes > 1) {
> -			if (bt->tc->processor >= nd->num_prstatus_notes)
> +			if (!nd->nt_prstatus_percpu[bt->tc->processor])
>  				error(FATAL, 
>  		          	    "cannot determine NT_PRSTATUS ELF note "
>  				    "for %s task: %lx\n",