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

[Chandru]

This thread relates to an old issue discussed  earlier here ... 
https://www.redhat.com/archives/crash-utility/2008-April/msg00007.html.
The following patch currently fixes the issue. The kernel cpu possible,present
and online cpu map is not available until cpu_maps_init() initializes them. Hence
we remap the nd->nt_prstatus_percpu array to online cpus right after a call to
this function. 


Signed-off-by: Chandru Siddalingappa <chandru at linux.vnet.ibm.com>
Cc: Haren Myneni <haren at us.ibm.com>
---

--- crash-4.0-8.10/ppc64.c.orig	2009-06-08 16:08:09.000000000 +0530
+++ crash-4.0-8.10/ppc64.c	2009-06-08 18:47:04.000000000 +0530
@@ -2407,13 +2407,11 @@ ppc64_paca_init(void)
 	if (!symbol_exists("paca"))
 		error(FATAL, "PPC64: Could not find 'paca' symbol\n");
 
-	if (cpu_map_addr("present"))
-		map = PRESENT;
-	else if (cpu_map_addr("online"))
-		map = ONLINE;
+	if (cpu_map_addr("possible"))
+		map = POSSIBLE;
 	else
 		error(FATAL, 
-		    "PPC64: cannot find 'cpu_present_map' or 'cpu_online_map' symbols\n");
+		    "PPC64: cannot find 'cpu_possible_map' symbol\n");
 
 	if (!MEMBER_EXISTS("paca_struct", "data_offset"))
 		return;
@@ -2424,7 +2422,7 @@ ppc64_paca_init(void)
 	cpu_paca_buf = GETBUF(SIZE(ppc64_paca));
 
 	if (!(nr_paca = get_array_length("paca", NULL, 0))) 
-		nr_paca = NR_CPUS;
+		nr_paca = kt->kernel_NR_CPUS;
 
 	if (nr_paca > NR_CPUS) {
 		error(WARNING, 
@@ -2435,7 +2433,7 @@ ppc64_paca_init(void)
 	
 	for (i = cpus = 0; i < nr_paca; i++) {
 		/*
-		 * CPU present (or online)?
+		 * CPU in possible map ?
 		 */
 		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	2009-06-08 16:48:53.000000000 +0530
@@ -74,6 +74,9 @@ kernel_init()
 
 	cpu_maps_init();
 
+	if (KDUMP_DUMPFILE())
+		map_prstatus_array();
+
 	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	2009-06-08 17:40:36.000000000 +0530
@@ -45,6 +45,35 @@ static void check_dumpfile_size(char *);
 	(machine_type("IA64") || machine_type("PPC64"))
 
 /*
+ * kdump installs NT_PRSTATUS elf sections 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 sections only to the online cpus
+ */
+void map_prstatus_array(void)
+{
+	void *nt_ptr;
+	int i, j;
+
+	/* 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);
+
+	/* re-populate the array with the sections mapping to online cpus */
+	for (i = 0, j = 0; i < kt->kernel_NR_CPUS; 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 +647,7 @@ 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 +2265,7 @@ 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",