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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:
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| 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.
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.