[PATCH 3/3] powerpc/pseries/mobility: rebuild cacheinfo hierarchy post-migration

[Nathan Lynch]

It's common for the platform to replace the cache device nodes after a
migration. Since the cacheinfo code is never informed about this, it
never drops its references to the source system's cache nodes, causing
it to wind up in an inconsistent state resulting in warnings and oopses
as soon as CPU online/offline occurs after the migration, e.g.

cache for /cpus/l3-cache at 3113(Unified) refers to cache for /cpus/l2-cache at 200d(Unified)
WARNING: CPU: 15 PID: 86 at arch/powerpc/kernel/cacheinfo.c:176 release_cache+0x1bc/0x1d0
[...]
NIP [c00000000002d9bc] release_cache+0x1bc/0x1d0
LR [c00000000002d9b8] release_cache+0x1b8/0x1d0
Call Trace:
[c0000001fc99fa70] [c00000000002d9b8] release_cache+0x1b8/0x1d0 (unreliable)
[c0000001fc99fb10] [c00000000002ebf4] cacheinfo_cpu_offline+0x1c4/0x2c0
[c0000001fc99fbe0] [c00000000002ae58] unregister_cpu_online+0x1b8/0x260
[c0000001fc99fc40] [c000000000165a64] cpuhp_invoke_callback+0x114/0xf40
[c0000001fc99fcd0] [c000000000167450] cpuhp_thread_fun+0x270/0x310
[c0000001fc99fd40] [c0000000001a8bb8] smpboot_thread_fn+0x2c8/0x390
[c0000001fc99fdb0] [c0000000001a1cd8] kthread+0x1b8/0x1c0
[c0000001fc99fe20] [c00000000000c2d4] ret_from_kernel_thread+0x5c/0x68

Using device tree notifiers won't work since we want to rebuild the
hierarchy only after all the removals and additions have occurred and
the device tree is in a consistent state. Call cacheinfo_teardown()
before processing device tree updates, and rebuild the hierarchy
afterward.

Fixes: 410bccf97881 ("powerpc/pseries: Partition migration in the kernel")
Signed-off-by: Nathan Lynch <nathanl at linux.ibm.com>
---
 arch/powerpc/platforms/pseries/mobility.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/powerpc/platforms/pseries/mobility.c b/arch/powerpc/platforms/pseries/mobility.c
index edc1ec408589..b8c8096907d4 100644
--- a/arch/powerpc/platforms/pseries/mobility.c
+++ b/arch/powerpc/platforms/pseries/mobility.c
@@ -23,6 +23,7 @@
 #include <asm/machdep.h>
 #include <asm/rtas.h>
 #include "pseries.h"
+#include "../../kernel/cacheinfo.h"
 
 static struct kobject *mobility_kobj;
 
@@ -345,11 +346,20 @@ void post_mobility_fixup(void)
 	 */
 	cpus_read_lock();
 
+	/*
+	 * It's common for the destination firmware to replace cache
+	 * nodes.  Release all of the cacheinfo hierarchy's references
+	 * before updating the device tree.
+	 */
+	cacheinfo_teardown();
+
 	rc = pseries_devicetree_update(MIGRATION_SCOPE);
 	if (rc)
 		printk(KERN_ERR "Post-mobility device tree update "
 			"failed: %d\n", rc);
 
+	cacheinfo_rebuild();
+
 	cpus_read_unlock();
 
 	/* Possibly switch to a new RFI flush type */
-- 
2.20.1