The patch titled
Subject: powerpc/64: initialise thread_info for emergency stacks
has been added to the -mm tree. Its filename is
powerpc-64-initialise-thread_info-for-emergency-stacks.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/powerpc-64-initialise-thread_info-for-emergency-stacks.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/powerpc-64-initialise-thread_info-for-emergency-stacks.patch
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------------------------------------------------------
From: Nicholas Piggin <npiggin@xxxxxxxxx>
Subject: powerpc/64: initialise thread_info for emergency stacks
Emergency stacks have their thread_info mostly uninitialised, which in
particular means garbage preempt_count values.
Emergency stack code runs with interrupts disabled entirely, and is used
very rarely, so this has been unnoticed so far. It was found by a
proposed new powerpc watchdog that takes a soft-NMI directly from the
masked_interrupt handler and using the emergency stack. That crashed at
BUG_ON(in_nmi()) in nmi_enter(). preempt_count()s were found to be
garbage.
This bug looks to be breaking linux-next on some powerpc boxes due to
interaction with a proposed new powerpc watchdog driver ("powerpc/64s:
implement arch-specific hardlockup watchdog").
Link: http://lkml.kernel.org/r/20170620135801.13272-1-npiggin@xxxxxxxxx
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Reported-by: Abdul Haleem <abdhalee@xxxxxxxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/powerpc/include/asm/thread_info.h | 19 +++++++++++++++++++
arch/powerpc/kernel/setup_64.c | 6 +++---
2 files changed, 22 insertions(+), 3 deletions(-)
diff -puN arch/powerpc/include/asm/thread_info.h~powerpc-64-initialise-thread_info-for-emergency-stacks arch/powerpc/include/asm/thread_info.h
--- a/arch/powerpc/include/asm/thread_info.h~powerpc-64-initialise-thread_info-for-emergency-stacks
+++ a/arch/powerpc/include/asm/thread_info.h
@@ -54,6 +54,7 @@ struct thread_info {
.task = &tsk, \
.cpu = 0, \
.preempt_count = INIT_PREEMPT_COUNT, \
+ .local_flags = 0, \
.flags = 0, \
}
@@ -62,6 +63,24 @@ struct thread_info {
#define THREAD_SIZE_ORDER (THREAD_SHIFT - PAGE_SHIFT)
+/*
+ * Emergency stacks are used for a range of things, from asynchronous
+ * NMIs (system reset, machine check) to synchronous, process context.
+ * Set HARDIRQ_OFFSET because we don't know exactly what context we
+ * come from or if it had a valid stack, which is about the best we
+ * can do.
+ * TODO: what to do with accounting?
+ */
+#define emstack_init_thread_info(ti, c) \
+do { \
+ (ti)->task = NULL; \
+ (ti)->cpu = (c); \
+ (ti)->preempt_count = HARDIRQ_OFFSET; \
+ (ti)->local_flags = 0; \
+ (ti)->flags = 0; \
+ klp_init_thread_info(ti); \
+} while (0)
+
/* how to get the thread information struct from C */
static inline struct thread_info *current_thread_info(void)
{
diff -puN arch/powerpc/kernel/setup_64.c~powerpc-64-initialise-thread_info-for-emergency-stacks arch/powerpc/kernel/setup_64.c
--- a/arch/powerpc/kernel/setup_64.c~powerpc-64-initialise-thread_info-for-emergency-stacks
+++ a/arch/powerpc/kernel/setup_64.c
@@ -639,18 +639,18 @@ void __init emergency_stack_init(void)
for_each_possible_cpu(i) {
struct thread_info *ti;
ti = __va(memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit));
- klp_init_thread_info(ti);
+ emstack_init_thread_info(ti, i);
paca[i].emergency_sp = (void *)ti + THREAD_SIZE;
#ifdef CONFIG_PPC_BOOK3S_64
/* emergency stack for NMI exception handling. */
ti = __va(memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit));
- klp_init_thread_info(ti);
+ emstack_init_thread_info(ti, i);
paca[i].nmi_emergency_sp = (void *)ti + THREAD_SIZE;
/* emergency stack for machine check exception handling. */
ti = __va(memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit));
- klp_init_thread_info(ti);
+ emstack_init_thread_info(ti, i);
paca[i].mc_emergency_sp = (void *)ti + THREAD_SIZE;
#endif
}
_
Patches currently in -mm which might be from npiggin@xxxxxxxxx are
watchdog-remove-unused-declaration.patch
watchdog-introduce-arch_touch_nmi_watchdog.patch
watchdog-split-up-config-options.patch
watchdog-split-up-config-options-fix.patch
watchdog-provide-watchdog_reconfigure-for-arch-watchdogs.patch
watchdog-provide-watchdog_reconfigure-for-arch-watchdogs-fix.patch
powerpc-64-initialise-thread_info-for-emergency-stacks.patch
powerpc-64s-implement-arch-specific-hardlockup-watchdog.patch
powerpc-64s-implement-arch-specific-hardlockup-watchdog-fix.patch
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