mirror of
https://github.com/hardkernel/linux.git
synced 2026-06-08 03:40:35 +09:00
035e304f95
[ Upstream commitc54c7374ff] 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>
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.