[PATCH] powerpc/kdump: fix kdump kernel hangup issue with hot add CPUs

[Sourabh Jain <sourabhjain@linux.ibm.com>]

With the kexec_file_load system call when system crashes on the hot add
CPU the capture kernel hangs and failed to collect the vmcore.

 Kernel panic - not syncing: sysrq triggered crash
 CPU: 24 PID: 6065 Comm: echo Kdump: loaded Not tainted 5.12.0-rc5upstream #54
 Call Trace:
 [c0000000e590fac0] [c0000000007b2400] dump_stack+0xc4/0x114 (unreliable)
 [c0000000e590fb00] [c000000000145290] panic+0x16c/0x41c
 [c0000000e590fba0] [c0000000008892e0] sysrq_handle_crash+0x30/0x40
 [c0000000e590fc00] [c000000000889cdc] __handle_sysrq+0xcc/0x1f0
 [c0000000e590fca0] [c00000000088a538] write_sysrq_trigger+0xd8/0x178
 [c0000000e590fce0] [c0000000005e9b7c] proc_reg_write+0x10c/0x1b0
 [c0000000e590fd10] [c0000000004f26d0] vfs_write+0xf0/0x330
 [c0000000e590fd60] [c0000000004f2aec] ksys_write+0x7c/0x140
 [c0000000e590fdb0] [c000000000031ee0] system_call_exception+0x150/0x290
 [c0000000e590fe10] [c00000000000ca5c] system_call_common+0xec/0x278
 --- interrupt: c00 at 0x7fff905b9664
 NIP:  00007fff905b9664 LR: 00007fff905320c4 CTR: 0000000000000000
 REGS: c0000000e590fe80 TRAP: 0c00   Not tainted  (5.12.0-rc5upstream)
 MSR:  800000000280f033 <SF,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE>  CR: 28000242
       XER: 00000000
 IRQMASK: 0
 GPR00: 0000000000000004 00007ffff5fedf30 00007fff906a7300 0000000000000001
 GPR04: 000001002a7355b0 0000000000000002 0000000000000001 00007ffff5fef616
 GPR08: 0000000000000001 0000000000000000 0000000000000000 0000000000000000
 GPR12: 0000000000000000 00007fff9073a160 0000000000000000 0000000000000000
 GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
 GPR20: 0000000000000000 00007fff906a4ee0 0000000000000002 0000000000000001
 GPR24: 00007fff906a0898 0000000000000000 0000000000000002 000001002a7355b0
 GPR28: 0000000000000002 00007fff906a1790 000001002a7355b0 0000000000000002
 NIP [00007fff905b9664] 0x7fff905b9664
 LR [00007fff905320c4] 0x7fff905320c4
 --- interrupt: c00

When a system crashes on a CPU the same CPU is used to boot the capture
kernel. On the capture kernel boot path, there is a check that ensures
that the boot CPU must be present in the fdt passed to it and if not it
calls the BUG function that leads to system hang. We do see the capture
kernel hang when we crash on hot added CPUs because the capture kernel
fdt does not have the information of newly added CPUs, here is why.

When we prepare fdt for capture kernel we copy most of the content from
the fdt passed to the primary kernel including cpus node data. The fdt
passed to the primary kernel is also referred to as initial_boot_params.
In case we hot add a CPU the initial_boot_params do not get updated with
the new CPU information. Although we do re-run the kdump service to update
the kdump on cpu hot-add event but as the capture kernel fdt is prepared
from the initial_boot_params it lacks the CPUs node for hot added CPUs.

To ensure that the capture kernel fdt has the latest CPUs information we
update the entire cpus and its subnode data in capture kernel fdt whenever
kdump service is reloaded on CPU hotplug event. The hot added CPU data is
extracted from of_root device node and update in the capture kernel while
adding additional nodes and properties needed for capture kernel.

Fixes: 6ecd0163d360 ("powerpc/kexec_file: Add appropriate regions for memory reserve map")

Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
---
 arch/powerpc/kexec/file_load_64.c | 100 ++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)

diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
index 02b9e4d0dc40..63a30f1ddc2c 100644
--- a/arch/powerpc/kexec/file_load_64.c
+++ b/arch/powerpc/kexec/file_load_64.c
@@ -960,6 +960,99 @@ unsigned int kexec_fdt_totalsize_ppc64(struct kimage *image)
 	return fdt_size;
 }
 
+/**
+ * add_node_prop - Read property from device node structure and add
+ *			them to fdt.
+ * @fdt:		Flattened device tree of the kernel
+ * @node_offset:	offset of the node to add a property at
+ * np:			device node pointer
+ *
+ * Returns 0 on success, negative errno on error.
+ */
+int add_node_prop(void *fdt, int node_offset, const struct device_node *np)
+{
+	int ret = 0;
+	struct property *pp;
+	unsigned long flags;
+
+	if (!np)
+		return -EINVAL;
+
+	raw_spin_lock_irqsave(&devtree_lock, flags);
+	for (pp = np->properties; pp; pp = pp->next) {
+		ret = fdt_setprop(fdt, node_offset, pp->name,
+				  pp->value, pp->length);
+		if (ret < 0) {
+			pr_err("Unable to add %s property: %s\n",
+				pp->name, fdt_strerror(ret));
+			goto out;
+		}
+	}
+out:
+	raw_spin_unlock_irqrestore(&devtree_lock, flags);
+	return ret;
+}
+
+/**
+ * update_cpus_node - Update cpus node of flattened device-tree using of_root
+ *			device node.
+ * @fdt:		Flattened device tree of the kernel.
+ *
+ * Returns 0 on success, negative errno on error.
+ */
+int update_cpus_node(void *fdt)
+{
+	struct device_node *cpus_node, *dn;
+	int cpus_offset, cpus_subnode_off, ret = 0;
+
+	cpus_offset = fdt_path_offset(fdt, "/cpus");
+	if (cpus_offset == -FDT_ERR_NOTFOUND || cpus_offset > 0) {
+		if (cpus_offset > 0) {
+			ret = fdt_del_node(fdt, cpus_offset);
+			if (ret < 0) {
+				pr_err("Error deleting /cpus node: %s\n",
+				       fdt_strerror(ret));
+				return -EINVAL;
+			}
+		}
+
+		/* Add cpus node to fdt */
+		cpus_offset = fdt_add_subnode(fdt, fdt_path_offset(fdt, "/"),
+					      "cpus");
+		if (cpus_offset < 0) {
+			pr_err("Error creating /cpus node: %s\n",
+			       fdt_strerror(cpus_offset));
+			return -EINVAL;
+		}
+
+		/* Add cpus node properties */
+		cpus_node = of_find_node_by_path("/cpus");
+		ret = add_node_prop(fdt, cpus_offset, cpus_node);
+		if (ret < 0)
+			return ret;
+
+		/* Loop through all subnodes of cpus and add them to fdt */
+		for_each_node_by_type(dn, "cpu") {
+			cpus_subnode_off = fdt_add_subnode(fdt,
+							   cpus_offset,
+							   dn->full_name);
+			if (cpus_subnode_off < 0) {
+				pr_err("Unable to add %s subnode: %s\n",
+				       dn->full_name, fdt_strerror(cpus_subnode_off));
+				return cpus_subnode_off;
+			}
+			ret = add_node_prop(fdt, cpus_subnode_off, dn);
+			if (ret < 0)
+				return ret;
+		}
+	} else if (cpus_offset < 0) {
+		pr_err("Malformed device tree: error reading /cpus node: %s\n",
+		       fdt_strerror(cpus_offset));
+	}
+
+	return ret;
+}
+
 /**
  * setup_new_fdt_ppc64 - Update the flattend device-tree of the kernel
  *                       being loaded.
@@ -1020,6 +1113,13 @@ int setup_new_fdt_ppc64(const struct kimage *image, void *fdt,
 		}
 	}
 
+	/* Update cpus nodes information to account hotplug CPUs. */
+	if (image->type == KEXEC_TYPE_CRASH) {
+		ret =  update_cpus_node(fdt);
+		if (ret < 0)
+			return ret;
+	}
+
 	/* Update memory reserve map */
 	ret = get_reserved_memory_ranges(&rmem);
 	if (ret)
-- 
2.26.3