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[PATCH 4.9 11/22] drm/dp/mst: fix kernel oops when turning off secondary monitor

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4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>

commit bb08c04dc867b5f392caec635c097d5d5fcd8c9f upstream.

100% reproducible issue found on SKL SkullCanyon NUC with two external
DP daisy-chained monitors in DP/MST mode. When turning off or changing
the input of the second monitor the machine stops with a kernel
oops. This issue happened with 4.8.8 as well as drm/drm-intel-nightly.

This issue is traced to an inconsistent control flow in
drm_dp_update_payload_part1(): the 'port' pointer is set to NULL at the
same time as 'req_payload.num_slots' is set to zero, but the pointer is
dereferenced even when req_payload.num_slot is zero.

The problematic dereference was introduced in commit dfda0df34
("drm/mst: rework payload table allocation to conform better") and may
impact all versions since v3.18

The fix suggested by Chris Wilson removes the kernel oops and was found to
work well after 10mn of monkey-testing with the second monitor power and
input buttons

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98990
Fixes: dfda0df34264 ("drm/mst: rework payload table allocation to conform better.")
Cc: Dave Airlie <airlied@redhat.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Nathan D Ciobanu <nathan.d.ciobanu@linux.intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Tested-by: Nathan D Ciobanu <nathan.d.ciobanu@linux.intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1487076561-2169-1-git-send-email-jani.nikula@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpu/drm/drm_dp_mst_topology.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1817,7 +1817,7 @@ int drm_dp_update_payload_part1(struct d
 				mgr->payloads[i].vcpi = req_payload.vcpi;
 			} else if (mgr->payloads[i].num_slots) {
 				mgr->payloads[i].num_slots = 0;
-				drm_dp_destroy_payload_step1(mgr, port, port->vcpi.vcpi, &mgr->payloads[i]);
+				drm_dp_destroy_payload_step1(mgr, port, mgr->payloads[i].vcpi, &mgr->payloads[i]);
 				req_payload.payload_state = mgr->payloads[i].payload_state;
 				mgr->payloads[i].start_slot = 0;
 			}

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[PATCH 4.9 00/22] 4.9.12-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 06/22] powerpc/64: Disable use of radix under a hypervisor Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 19/22] ntb: ntb_perf missing dmaengine_unmap_put Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 13/22] ARM: 8658/1: uaccess: fix zeroing of 64-bit get_user() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 16/22] printk: use rcuidle console tracepoint Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 17/22] timekeeping: Use deferred printk() in debug code Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 22/22] [media] videodev2.h: go back to limited range YCbCr for SRGB and, ADOBERGB Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 08/22] Fix missing sanity check in /dev/sg Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 21/22] bcache: Make gc wakeup sane, remove set_task_state() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 07/22] scsi: dont BUG_ON() empty DMA transfers Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 09/22] Input: elan_i2c - add ELAN0605 to the ACPI table Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 12/22] futex: Move futex_init() to core_initcall Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 02/22] [media] siano: make it work again with CONFIG_VMAP_STACK Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 14/22] Revert "i2c: designware: detect when dynamic tar update is possible" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 01/22] vfs: fix uninitialized flags in splice_to_pipe() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 04/22] fuse: fix uninitialized flags in pipe_buffer Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 20/22] ntb_transport: Pick an unused queue Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 18/22] NTB: ntb_transport: fix debugfs_remove_recursive Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 05/22] mmc: core: fix multi-bit bus width without high-speed mode Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:10 +0100
  [PATCH 4.9 11/22] drm/dp/mst: fix kernel oops when turning off secondary monitor Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-21 14:20 +0100
  Re: [PATCH 4.9 00/22] 4.9.12-stable review Guenter Roeck <linux@roeck-us.net> - 2017-02-21 17:20 +0100
    Re: [PATCH 4.9 00/22] 4.9.12-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-23 18:00 +0100
  Re: [PATCH 4.9 00/22] 4.9.12-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-02-22 00:50 +0100
    Re: [PATCH 4.9 00/22] 4.9.12-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-23 18:00 +0100
  Re: [PATCH 4.9 00/22] 4.9.12-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-23 18:00 +0100

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