[Utopic][SRU][PATCH] powerpc/kdump: Ignore failure in enabling big endian exception during crash

[Chris J Arges]

From: Hari Bathini <hbathini at linux.vnet.ibm.com>

BugLink: http://bugs.launchpad.net/bugs/1410817

In LE kernel, we currently have a hack for kexec that resets the exception
endian before starting a new kernel as the kernel that is loaded could be a
big endian or a little endian kernel. In kdump case, resetting exception
endian fails when one or more cpus is disabled. But we can ignore the failure
and still go ahead, as in most cases crashkernel will be of same endianess
as primary kernel and reseting endianess is not even needed in those cases.
This patch adds a new inline function to say if this is kdump path. This
function is used at places where such a check is needed.

Signed-off-by: Hari Bathini <hbathini at linux.vnet.ibm.com>
[mpe: Rename to kdump_in_progress(), use bool, and edit comment]
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>

(cherry picked from commit c1caae3de46a072d0855729aed6e793e536a4a55)
Signed-off-by: Chris J Arges <chris.j.arges at canonical.com>
---
 arch/powerpc/include/asm/kexec.h       | 10 ++++++++++
 arch/powerpc/kernel/machine_kexec_64.c |  2 +-
 arch/powerpc/platforms/pseries/lpar.c  |  8 +++++++-
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/kexec.h b/arch/powerpc/include/asm/kexec.h
index 16d7e33..cd4570d 100644
--- a/arch/powerpc/include/asm/kexec.h
+++ b/arch/powerpc/include/asm/kexec.h
@@ -87,6 +87,11 @@ extern int overlaps_crashkernel(unsigned long start, unsigned long size);
 extern void reserve_crashkernel(void);
 extern void machine_kexec_mask_interrupts(void);
 
+static inline bool kdump_in_progress(void)
+{
+	return crashing_cpu >= 0;
+}
+
 #else /* !CONFIG_KEXEC */
 static inline void crash_kexec_secondary(struct pt_regs *regs) { }
 
@@ -107,6 +112,11 @@ static inline int crash_shutdown_unregister(crash_shutdown_t handler)
 	return 0;
 }
 
+static inline bool kdump_in_progress(void)
+{
+	return false;
+}
+
 #endif /* CONFIG_KEXEC */
 #endif /* ! __ASSEMBLY__ */
 #endif /* __KERNEL__ */
diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
index a670bf4..eedc904 100644
--- a/arch/powerpc/kernel/machine_kexec_64.c
+++ b/arch/powerpc/kernel/machine_kexec_64.c
@@ -264,7 +264,7 @@ void default_machine_kexec(struct kimage *image)
         * using debugger IPI.
         */
 
-	if (crashing_cpu == -1)
+	if (!kdump_in_progress())
 		kexec_prepare_cpus();
 
 	pr_debug("kexec: Starting switchover sequence.\n");
diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index cd50be6..faa7f93 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -42,6 +42,7 @@
 #include <asm/trace.h>
 #include <asm/firmware.h>
 #include <asm/plpar_wrappers.h>
+#include <asm/kexec.h>
 #include <asm/fadump.h>
 
 #include "pseries.h"
@@ -268,8 +269,13 @@ static void pSeries_lpar_hptab_clear(void)
 		 * out to the user, but at least this will stop us from
 		 * continuing on further and creating an even more
 		 * difficult to debug situation.
+		 *
+		 * There is a known problem when kdump'ing, if cpus are offline
+		 * the above call will fail. Rather than panicking again, keep
+		 * going and hope the kdump kernel is also little endian, which
+		 * it usually is.
 		 */
-		if (rc)
+		if (rc && !kdump_in_progress())
 			panic("Could not enable big endian exceptions");
 	}
 #endif
-- 
1.9.1