Merge tag 'v4.9.220' into 4.9-2.3.x-imx

This is the 4.9.220 stable release

Conflicts:
	arch/arm/Kconfig.debug
	arch/arm/boot/dts/imx7s.dtsi
	arch/arm/mach-imx/common.h
	arch/arm/mach-imx/cpuidle-imx6q.c
	arch/arm/mach-imx/cpuidle-imx6sx.c
	arch/arm/mach-imx/suspend-imx6.S
	block/blk-core.c
	drivers/crypto/caam/caamalg.c
	drivers/crypto/mxs-dcp.c
	drivers/dma/imx-sdma.c
	drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
	drivers/input/keyboard/imx_keypad.c
	drivers/input/keyboard/snvs_pwrkey.c
	drivers/mmc/host/sdhci.c
	drivers/net/can/flexcan.c
	drivers/net/ethernet/freescale/fec_main.c
	drivers/net/phy/phy_device.c
	drivers/net/wireless/ath/ath10k/pci.c
	drivers/tty/serial/imx.c
	drivers/usb/dwc3/gadget.c
	drivers/usb/host/xhci.c
	include/linux/blkdev.h
	include/linux/cpu.h
	include/linux/platform_data/dma-imx-sdma.h
	kernel/cpu.c
	net/wireless/util.c
	sound/soc/fsl/Kconfig
	sound/soc/fsl/fsl_esai.c
	sound/soc/fsl/fsl_sai.c
	sound/soc/fsl/imx-sgtl5000.c

1 files changed, 29 insertions, 4 deletions

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 99becab2c1ce..8e8b903b7613 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -49,14 +49,30 @@ static void perf_output_put_handle(struct perf_output_handle *handle)
 	unsigned long head;
 
 again:
+	/*
+	 * In order to avoid publishing a head value that goes backwards,
+	 * we must ensure the load of @rb->head happens after we've
+	 * incremented @rb->nest.
+	 *
+	 * Otherwise we can observe a @rb->head value before one published
+	 * by an IRQ/NMI happening between the load and the increment.
+	 */
+	barrier();
 	head = local_read(&rb->head);
 
 	/*
-	 * IRQ/NMI can happen here, which means we can miss a head update.
+	 * IRQ/NMI can happen here and advance @rb->head, causing our
+	 * load above to be stale.
 	 */
 
-	if (!local_dec_and_test(&rb->nest))
+	/*
+	 * If this isn't the outermost nesting, we don't have to update
+	 * @rb->user_page->data_head.
+	 */
+	if (local_read(&rb->nest) > 1) {
+		local_dec(&rb->nest);
 		goto out;
+	}
 
 	/*
 	 * Since the mmap() consumer (userspace) can run on a different CPU:
@@ -88,9 +104,18 @@ again:
 	rb->user_page->data_head = head;
 
 	/*
-	 * Now check if we missed an update -- rely on previous implied
-	 * compiler barriers to force a re-read.
+	 * We must publish the head before decrementing the nest count,
+	 * otherwise an IRQ/NMI can publish a more recent head value and our
+	 * write will (temporarily) publish a stale value.
+	 */
+	barrier();
+	local_set(&rb->nest, 0);
+
+	/*
+	 * Ensure we decrement @rb->nest before we validate the @rb->head.
+	 * Otherwise we cannot be sure we caught the 'last' nested update.
 	 */
+	barrier();
 	if (unlikely(head != local_read(&rb->head))) {
 		local_inc(&rb->nest);
 		goto again;