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Lyude Paul 035e304f95 drm/dp_mst: Skip validating ports during destruction, just ref 
[ Upstream commit c54c7374ff ]

Jerry Zuo pointed out a rather obscure hotplugging issue that it seems I
accidentally introduced into DRM two years ago.

Pretend we have a topology like this:

|- DP-1: mst_primary
   |- DP-4: active display
   |- DP-5: disconnected
   |- DP-6: active hub
      |- DP-7: active display
      |- DP-8: disconnected
      |- DP-9: disconnected

If we unplug DP-6, the topology starting at DP-7 will be destroyed but
it's payloads will live on in DP-1's VCPI allocations and thus require
removal. However, this removal currently fails because
drm_dp_update_payload_part1() will (rightly so) try to validate the port
before accessing it, fail then abort. If we keep going, eventually we
run the MST hub out of bandwidth and all new allocations will start to
fail (or in my case; all new displays just start flickering a ton).

We could just teach drm_dp_update_payload_part1() not to drop the port
ref in this case, but then we also need to teach
drm_dp_destroy_payload_step1() to do the same thing, then hope no one
ever adds anything to the that requires a validated port reference in
drm_dp_destroy_connector_work(). Kind of sketchy.

So let's go with a more clever solution: any port that
drm_dp_destroy_connector_work() interacts with is guaranteed to still
exist in memory until we say so. While said port might not be valid we
don't really care: that's the whole reason we're destroying it in the
first place! So, teach drm_dp_get_validated_port_ref() to use the all
mighty current_work() function to avoid attempting to validate ports
from the context of mgr->destroy_connector_work. I can't see any
situation where this wouldn't be safe, and this avoids having to play
whack-a-mole in the future of trying to work around port validation.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Fixes: 263efde31f ("drm/dp/mst: Get validated port ref in drm_dp_update_payload_part1()")
Reported-by: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Harry Wentland <Harry.Wentland@amd.com>
Cc: <stable@vger.kernel.org> # v4.6+
Reviewed-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181113224613.28809-1-lyude@redhat.com
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2020-01-27 14:50:03 +01:00
arch ARM: dts: bcm283x: Correct mailbox register sizes 2020-01-27 14:50:01 +01:00
block block: fix an integer overflow in logical block size 2020-01-23 08:21:29 +01:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto pcrypt: use format specifier in kobject_add 2020-01-27 14:50:02 +01:00
Documentation bus: ti-sysc: Add mcasp optional clocks flag 2020-01-27 14:50:02 +01:00
drivers drm/dp_mst: Skip validating ports during destruction, just ref 2020-01-27 14:50:03 +01:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:21:29 +01:00
fs exportfs: fix 'passing zero to ERR_PTR()' warning 2020-01-27 14:50:02 +01:00
include ASoC: wm97xx: fix uninitialized regmap pointer problem 2020-01-27 14:50:01 +01:00
init fork: fix some -Wmissing-prototypes warnings 2019-12-05 09:21:04 +01:00
ipc ipc/mqueue.c: only perform resource calculation if user valid 2019-08-06 19:06:52 +02:00
kernel genirq/debugfs: Reinstate full OF path for domain name 2020-01-27 14:49:56 +01:00
lib idr: Fix idr_get_next_ul race with idr_remove 2019-12-17 20:36:02 +01:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mm/huge_memory.c: thp: fix conflict of above-47bit hint address and PMD alignment 2020-01-23 08:21:32 +01:00
net net: always initialize pagedlen 2020-01-27 14:50:03 +01:00
samples samples: bpf: fix syscall_tp due to unused syscall 2020-01-12 12:17:13 +01:00
scripts kconfig: don't crash on NULL expressions in expr_eq() 2020-01-12 12:17:19 +01:00
security apparmor: don't try to replace stale label in ptrace access check 2020-01-27 14:49:55 +01:00
sound ASoC: sun8i-codec: add missing route for ADC 2020-01-27 14:50:02 +01:00
tools perf map: No need to adjust the long name of modules 2020-01-27 14:49:53 +01:00
usr kbuild: clean compressed initramfs image 2019-10-07 18:57:16 +02:00
virt KVM: arm/arm64: vgic: Don't rely on the wrong pending table 2019-12-13 08:52:45 +01:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS USB: rio500: Remove Rio 500 kernel driver 2019-10-17 13:44:47 -07:00
Makefile Linux 4.19.98 2020-01-23 08:21:39 +01:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.