ARM: prevent tracing IPI_CPU_BACKTRACE

Patch series "compiler: allow all arches to enable
CONFIG_OPTIMIZE_INLINING", v3.

This patch (of 11):

When function tracing for IPIs is enabled, we get a warning for an
overflow of the ipi_types array with the IPI_CPU_BACKTRACE type as
triggered by raise_nmi():

  arch/arm/kernel/smp.c: In function 'raise_nmi':
  arch/arm/kernel/smp.c:489:2: error: array subscript is above array bounds [-Werror=array-bounds]
    trace_ipi_raise(target, ipi_types[ipinr]);

This is a correct warning as we actually overflow the array here.

This patch raise_nmi() to call __smp_cross_call() instead of
smp_cross_call(), to avoid calling into ftrace.  For clarification, I'm
also adding a two new code comments describing how this one is special.

The warning appears to have shown up after commit e7273ff49acf ("ARM:
8488/1: Make IPI_CPU_BACKTRACE a "non-secure" SGI"), which changed the
number assignment from '15' to '8', but as far as I can tell has existed
since the IPI tracepoints were first introduced.  If we decide to
backport this patch to stable kernels, we probably need to backport
e7273ff49acf as well.

[[email protected]: rebase on v5.1-rc1]
Link: http://lkml.kernel.org/r/[email protected]
Fixes: e7273ff49acf ("ARM: 8488/1: Make IPI_CPU_BACKTRACE a "non-secure" SGI")
Fixes: 365ec7b17327 ("ARM: add IPI tracepoints") # v3.17
Signed-off-by: Arnd Bergmann <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Mathieu Malaterre <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Stefan Agner <[email protected]>
Cc: Boris Brezillon <[email protected]>
Cc: Miquel Raynal <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: Brian Norris <[email protected]>
Cc: Marek Vasut <[email protected]>
Cc: Russell King <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Mark Rutland <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

2 files changed, 6 insertions, 1 deletions

diff --git a/arch/arm/include/asm/hardirq.h b/arch/arm/include/asm/hardirq.h
index cba23eaa6072..7a88f160b1fb 100644
--- a/arch/arm/include/asm/hardirq.h
+++ b/arch/arm/include/asm/hardirq.h
@@ -6,6 +6,7 @@
 #include <linux/threads.h>
 #include <asm/irq.h>
 
+/* number of IPIS _not_ including IPI_CPU_BACKTRACE */
 #define NR_IPI	7
 
 typedef struct {
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index facd4240ca02..c93fe0f256de 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -70,6 +70,10 @@ enum ipi_msg_type {
 	IPI_CPU_STOP,
 	IPI_IRQ_WORK,
 	IPI_COMPLETION,
+	/*
+	 * CPU_BACKTRACE is special and not included in NR_IPI
+	 * or tracable with trace_ipi_*
+	 */
 	IPI_CPU_BACKTRACE,
 	/*
 	 * SGI8-15 can be reserved by secure firmware, and thus may
@@ -797,7 +801,7 @@ core_initcall(register_cpufreq_notifier);
 
 static void raise_nmi(cpumask_t *mask)
 {
-	smp_cross_call(mask, IPI_CPU_BACKTRACE);
+	__smp_cross_call(mask, IPI_CPU_BACKTRACE);
 }
 
 void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)