sreset driven panic/oops message printing fixes

The die() oops path contains a serializing lock to prevent oops messages from being interleaved. In the case of a system reset initiated oops (e.g., qemu nmi command), __die was being called which lacks that synchronisation and oops reports could be interleaved across CPUs.

A recent patch 4388c9b3a6ee7 ("powerpc: Do not send system reset request through the oops path") changed this to __die to avoid the debugger() call, but there is no real harm to calling it twice if the first time fell through. So go back to using die() here. This was observed to fix the problem.

Fixes 4388c9b3a6ee7 ("powerpc: Do not send system reset request through the oops path")

Signed-off-by Nicholas Piggin <[email protected]>

---
 arch/powerpc/kernel/traps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

arch/powerpc/kernel/traps.c +1 -1

index f3eb61be0d30..109989676776 100644
@@ -337,7 +337,7 @@ void system_reset_exception(struct pt_regs *regs)
 	 * No debugger or crash dump registered, print logs then
 	 * panic.
 	 */
-	__die("System Reset", regs, SIGABRT);
+	die("System Reset", regs, SIGABRT);
 
 	mdelay(2*MSEC_PER_SEC); /* Wait a little while for others to print */
 	add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);

The die() oops path contains a serializing lock to prevent oops messages from being interleaved. In the case of a system reset initiated oops (e.g., qemu nmi command), __die was being called which lacks that synchronisation and oops reports could be interleaved across CPUs.

A recent patch 4388c9b3a6ee7 ("powerpc: Do not send system reset request through the oops path") changed this to __die to avoid the debugger() call, but there is no real harm to calling it twice if the first time fell through. So go back to using die() here. This was observed to fix the problem.

Fixes 4388c9b3a6ee7 ("powerpc: Do not send system reset request through the oops path")

Signed-off-by Nicholas Piggin <[email protected]>

Reviewed-by David Gibson <[email protected]>

Platforms with a panic handler that halts the system can have problems getting kernel messages out, because the panic notifiers are called before kernel/panic.c does its flushing of printk buffers an console etc.

This was attempted to be solved with commit a3b2cb30f252 ("powerpc: Do not call ppc_md.panic in fadump panic notifier"), but that wasn't the right approach and caused other problems, and was reverted by commit ab9dbf771ff9.

Instead, the powernv shutdown paths have already had a similar problem, fixed by taking the message flushing sequence from kernel/panic.c. That's a little bit ugly, but while we have the code duplicated, it will work for this case as well. So have ppc panic handlers do the same flushing before they terminate.

Without this patch, a qemu pseries_le_defconfig guest stops silently when issued the nmi command when xmon is off and no crash dumpers enabled. Afterwards, an oops is printed by each CPU as expected.

Fixes ab9dbf771ff9 ("Revert "powerpc: Do not call ppc_md.panic in fadump panic notifier"")

Signed-off-by Nicholas Piggin <[email protected]>

---
 arch/powerpc/include/asm/bug.h         |  3 ++-
 arch/powerpc/kernel/traps.c            | 24 ++++++++++++++++++++++++
 arch/powerpc/platforms/powernv/opal.c  | 18 ++++--------------
 arch/powerpc/platforms/ps3/setup.c     |  1 +
 arch/powerpc/platforms/pseries/setup.c |  8 +++++++-
 5 files changed, 38 insertions(+), 16 deletions(-)

arch/powerpc/include/asm/bug.h +2 -1

index 3c04249bcf39..bca101ee1f32 100644
@@ -135,7 +135,8 @@ extern void bad_page_fault(struct pt_regs *, unsigned long, int);
 extern void _exception(int, struct pt_regs *, int, unsigned long);
 extern void die(const char *, struct pt_regs *, long);
 extern bool die_will_crash(void);
-
+extern void panic_flush_kmsg_start(void);
+extern void panic_flush_kmsg_end(void);
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __KERNEL__ */

arch/powerpc/kernel/traps.c +24 -0

index 109989676776..37c1ea9b0642 100644
@@ -38,6 +38,8 @@
 #include <linux/ratelimit.h>
 #include <linux/context_tracking.h>
 #include <linux/smp.h>
+#include <linux/console.h>
+#include <linux/kmsg_dump.h>
 
 #include <asm/emulated_ops.h>
 #include <asm/pgtable.h>

@@ -142,6 +144,28 @@ static int die_owner = -1;
 static unsigned int die_nest_count;
 static int die_counter;
 
+extern void panic_flush_kmsg_start(void)
+{
+	/*
+	 * These are mostly taken from kernel/panic.c, but tries to do
+	 * relatively minimal work. Don't use delay functions (TB may
+	 * be broken), don't crash dump (need to set a firmware log),
+	 * don't run notifiers. We do want to get some information to
+	 * Linux console.
+	 */
+	console_verbose();
+	bust_spinlocks(1);
+}
+
+extern void panic_flush_kmsg_end(void)
+{
+	printk_safe_flush_on_panic();
+	kmsg_dump(KMSG_DUMP_PANIC);
+	bust_spinlocks(0);
+	debug_locks_off();
+	console_flush_on_panic();
+}
+
 static unsigned long oops_begin(struct pt_regs *regs)
 {
 	int cpu;

arch/powerpc/platforms/powernv/opal.c +4 -14

index 69b5263fc9e3..c15182765ff5 100644
@@ -461,24 +461,14 @@ static int opal_recover_mce(struct pt_regs *regs,
 
 void pnv_platform_error_reboot(struct pt_regs *regs, const char *msg)
 {
-	/*
-	 * This is mostly taken from kernel/panic.c, but tries to do
-	 * relatively minimal work. Don't use delay functions (TB may
-	 * be broken), don't crash dump (need to set a firmware log),
-	 * don't run notifiers. We do want to get some information to
-	 * Linux console.
-	 */
-	console_verbose();
-	bust_spinlocks(1);
+	panic_flush_kmsg_start();
+
 	pr_emerg("Hardware platform error: %s\n", msg);
 	if (regs)
 		show_regs(regs);
 	smp_send_stop();
-	printk_safe_flush_on_panic();
-	kmsg_dump(KMSG_DUMP_PANIC);
-	bust_spinlocks(0);
-	debug_locks_off();
-	console_flush_on_panic();
+
+	panic_flush_kmsg_end();
 
 	/*
 	 * Don't bother to shut things down because this will

arch/powerpc/platforms/ps3/setup.c +1 -0

index 6244bc849469..77a37520068d 100644
@@ -113,6 +113,7 @@ static void ps3_panic(char *str)
 	printk("   System does not reboot automatically.\n");
 	printk("   Please press POWER button.\n");
 	printk("\n");
+	panic_flush_kmsg_end();
 
 	while(1)
 		lv1_pause(1);

arch/powerpc/platforms/pseries/setup.c +7 -1

index 28b286df0e91..a65843059c38 100644
@@ -498,6 +498,12 @@ static void __init pSeries_setup_arch(void)
 	ppc_md.pcibios_root_bridge_prepare = pseries_root_bridge_prepare;
 }
 
+static void pSeries_panic(char *str)
+{
+	panic_flush_kmsg_end();
+	rtas_os_term(str);
+}
+
 static int __init pSeries_init_panel(void)
 {
 	/* Manually leave the kernel version on the panel. */

@@ -726,7 +732,7 @@ define_machine(pseries) {
 	.pcibios_fixup		= pSeries_final_fixup,
 	.restart		= rtas_restart,
 	.halt			= rtas_halt,
-	.panic			= rtas_os_term,
+	.panic			= pSeries_panic,
 	.get_boot_time		= rtas_get_boot_time,
 	.get_rtc_time		= rtas_get_rtc_time,
 	.set_rtc_time		= rtas_set_rtc_time,

Platforms with a panic handler that halts the system can have problems getting kernel messages out, because the panic notifiers are called before kernel/panic.c does its flushing of printk buffers an console etc.

This was attempted to be solved with commit a3b2cb30f252 ("powerpc: Do not call ppc_md.panic in fadump panic notifier"), but that wasn't the right approach and caused other problems, and was reverted by commit ab9dbf771ff9.

Instead, the powernv shutdown paths have already had a similar problem, fixed by taking the message flushing sequence from kernel/panic.c. That's a little bit ugly, but while we have the code duplicated, it will work for this case as well. So have ppc panic handlers do the same flushing before they terminate.

Without this patch, a qemu pseries_le_defconfig guest stops silently when issued the nmi command when xmon is off and no crash dumpers enabled. Afterwards, an oops is printed by each CPU as expected.

Fixes ab9dbf771ff9 ("Revert "powerpc: Do not call ppc_md.panic in fadump panic notifier"")

Signed-off-by Nicholas Piggin <[email protected]>

Reviewed-by David Gibson <[email protected]>