commit a337b64f0d5717248a0c894e2618e658e6a9de9f upstream.
Infinite waits for completion of GPU activity have been observed in CI,
mostly inside __i915_active_wait(), triggered by igt@gem_barrier_race or
igt@perf@stress-open-close. Root cause analysis, based of ftrace dumps
generated with a lot of extra trace_printk() calls added to the code,
revealed loops of request dependencies being accidentally built,
preventing the requests from being processed, each waiting for completion
of another one's activity.
After we substitute a new request for a last active one tracked on a
timeline, we set up a dependency of our new request to wait on completion
of current activity of that previous one. While doing that, we must take
care of keeping the old request still in memory until we use its
attributes for setting up that await dependency, or we can happen to set
up the await dependency on an unrelated request that already reuses the
memory previously allocated to the old one, already released. Combined
with perf adding consecutive kernel context remote requests to different
user context timelines, unresolvable loops of await dependencies can be
built, leading do infinite waits.
We obtain a pointer to the previous request to wait upon when we
substitute it with a pointer to our new request in an active tracker,
e.g. in intel_timeline.last_request. In some processing paths we protect
that old request from being freed before we use it by getting a reference
to it under RCU protection, but in others, e.g. __i915_request_commit()
-> __i915_request_add_to_timeline() -> __i915_request_ensure_ordering(),
we don't. But anyway, since the requests' memory is SLAB_FAILSAFE_BY_RCU,
that RCU protection is not sufficient against reuse of memory.
We could protect i915_request's memory from being prematurely reused by
calling its release function via call_rcu() and using rcu_read_lock()
consequently, as proposed in v1. However, that approach leads to
significant (up to 10 times) increase of SLAB utilization by i915_request
SLAB cache. Another potential approach is to take a reference to the
previous active fence.
When updating an active fence tracker, we first lock the new fence,
substitute a pointer of the current active fence with the new one, then we
lock the substituted fence. With this approach, there is a time window
after the substitution and before the lock when the request can be
concurrently released by an interrupt handler and its memory reused, then
we may happen to lock and return a new, unrelated request.
Always get a reference to the current active fence first, before
replacing it with a new one. Having it protected from premature release
and reuse, lock it and then replace with the new one but only if not
yet signalled via a potential concurrent interrupt nor replaced with
another one by a potential concurrent thread, otherwise retry, starting
from getting a reference to the new current one. Adjust users to not
get a reference to the previous active fence themselves and always put the
reference got by __i915_active_fence_set() when no longer needed.
v3: Fix lockdep splat reports and other issues caused by incorrect use of
try_cmpxchg() (use (cmpxchg() != prev) instead)
v2: Protect request's memory by getting a reference to it in favor of
delegating its release to call_rcu() (Chris)
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/8211
Fixes: df9f85d858 ("drm/i915: Serialise i915_active_fence_set() with itself")
Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Cc: <stable@vger.kernel.org> # v5.6+
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230720093543.832147-2-janusz.krzysztofik@linux.intel.com
(cherry picked from commit 946e047a3d88d46d15b5c5af0414098e12b243f7)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit e0e6b416b25ee14716f3549e0cbec1011b193809 upstream.
Users reported oopses on list corruptions when using i915 perf with a
number of concurrently running graphics applications. Root cause analysis
pointed at an issue in barrier processing code -- a race among perf open /
close replacing active barriers with perf requests on kernel context and
concurrent barrier preallocate / acquire operations performed during user
context first pin / last unpin.
When adding a request to a composite tracker, we try to reuse an existing
fence tracker, already allocated and registered with that composite. The
tracker we obtain may already track another fence, may be an idle barrier,
or an active barrier.
If the tracker we get occurs a non-idle barrier then we try to delete that
barrier from a list of barrier tasks it belongs to. However, while doing
that we don't respect return value from a function that performs the
barrier deletion. Should the deletion ever fail, we would end up reusing
the tracker still registered as a barrier task. Since the same structure
field is reused with both fence callback lists and barrier tasks list,
list corruptions would likely occur.
Barriers are now deleted from a barrier tasks list by temporarily removing
the list content, traversing that content with skip over the node to be
deleted, then populating the list back with the modified content. Should
that intentionally racy concurrent deletion attempts be not serialized,
one or more of those may fail because of the list being temporary empty.
Related code that ignores the results of barrier deletion was initially
introduced in v5.4 by commit d8af05ff38 ("drm/i915: Allow sharing the
idle-barrier from other kernel requests"). However, all users of the
barrier deletion routine were apparently serialized at that time, then the
issue didn't exhibit itself. Results of git bisect with help of a newly
developed igt@gem_barrier_race@remote-request IGT test indicate that list
corruptions might start to appear after commit 311770173f ("drm/i915/gt:
Schedule request retirement when timeline idles"), introduced in v5.5.
Respect results of barrier deletion attempts -- mark the barrier as idle
only if successfully deleted from the list. Then, before proceeding with
setting our fence as the one currently tracked, make sure that the tracker
we've got is not a non-idle barrier. If that check fails then don't use
that tracker but go back and try to acquire a new, usable one.
v3: use unlikely() to document what outcome we expect (Andi),
- fix bad grammar in commit description.
v2: no code changes,
- blame commit 311770173f ("drm/i915/gt: Schedule request retirement
when timeline idles"), v5.5, not commit d8af05ff38 ("drm/i915: Allow
sharing the idle-barrier from other kernel requests"), v5.4,
- reword commit description.
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/6333
Fixes: 311770173f ("drm/i915/gt: Schedule request retirement when timeline idles")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@vger.kernel.org # v5.5
Cc: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230302120820.48740-1-janusz.krzysztofik@linux.intel.com
(cherry picked from commit 506006055769b10d1b2b4e22f636f3b45e0e9fc7)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit f6e98a1809faa02f40e0d089d6cfc1aa372a34c0 upstream.
The first thing the active retirement worker does is decrement the
i915_active count.
The first thing we do during i915_active_wait is try to increment the
i915_active count, but only if already active [non-zero].
The wait may see that the retirement is already started and so marked the
i915_active as idle, and skip waiting for the retirement handler.
However, the caller of i915_active_wait may immediately free the
i915_active upon returning (e.g. i915_vma_destroy) so we must not return
before the concurrent access from the worker is completed. We must
always flush the worker.
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2473
Fixes: 274cbf20fd ("drm/i915: Push the i915_active.retire into a worker")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: <stable@vger.kernel.org> # v5.5+
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210121232807.16618-1-chris@chris-wilson.co.uk
(cherry picked from commit 977a372e972cb42799746c284035a33c64ebace9)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Pull drm updates from Dave Airlie:
"Not a major amount of change, the i915 trees got split into display
and gt trees to better facilitate higher level review, and there's a
major refactoring of i915 GEM locking to use more core kernel concepts
(like ww-mutexes). msm gets per-process pagetables, older AMD SI cards
get DC support, nouveau got a bump in displayport support with common
code extraction from i915.
Outside of drm this contains a couple of patches for hexint
moduleparams which you've acked, and a virtio common code tree that
you should also get via it's regular path.
New driver:
- Cadence MHDP8546 DisplayPort bridge driver
core:
- cross-driver scatterlist cleanups
- devm_drm conversions
- remove drm_dev_init
- devm_drm_dev_alloc conversion
ttm:
- lots of refactoring and cleanups
bridges:
- chained bridge support in more drivers
panel:
- misc new panels
scheduler:
- cleanup priority levels
displayport:
- refactor i915 code into helpers for nouveau
i915:
- split into display and GT trees
- WW locking refactoring in GEM
- execbuf2 extension mechanism
- syncobj timeline support
- GEN 12 HOBL display powersaving
- Rocket Lake display additions
- Disable FBC on Tigerlake
- Tigerlake Type-C + DP improvements
- Hotplug interrupt refactoring
amdgpu:
- Sienna Cichlid updates
- Navy Flounder updates
- DCE6 (SI) support for DC
- Plane rotation enabled
- TMZ state info ioctl
- PCIe DPC recovery support
- DC interrupt handling refactor
- OLED panel fixes
amdkfd:
- add SMI events for thermal throttling
- SMI interface events ioctl update
- process eviction counters
radeon:
- move to dma_ for allocations
- expose sclk via sysfs
msm:
- DSI support for sm8150/sm8250
- per-process GPU pagetable support
- Displayport support
mediatek:
- move HDMI phy driver to PHY
- convert mtk-dpi to bridge API
- disable mt2701 tmds
tegra:
- bridge support
exynos:
- misc cleanups
vc4:
- dual display cleanups
ast:
- cleanups
gma500:
- conversion to GPIOd API
hisilicon:
- misc reworks
ingenic:
- clock handling and format improvements
mcde:
- DSI support
mgag200:
- desktop g200 support
mxsfb:
- i.MX7 + i.MX8M
- alpha plane support
panfrost:
- devfreq support
- amlogic SoC support
ps8640:
- EDID from eDP retrieval
tidss:
- AM65xx YUV workaround
virtio:
- virtio-gpu exported resources
rcar-du:
- R8A7742, R8A774E1 and R8A77961 support
- YUV planar format fixes
- non-visible plane handling
- VSP device reference count fix
- Kconfig fix to avoid displaying disabled options in .config"
* tag 'drm-next-2020-10-15' of git://anongit.freedesktop.org/drm/drm: (1494 commits)
drm/ingenic: Fix bad revert
drm/amdgpu: Fix invalid number of character '{' in amdgpu_acpi_init
drm/amdgpu: Remove warning for virtual_display
drm/amdgpu: kfd_initialized can be static
drm/amd/pm: setup APU dpm clock table in SMU HW initialization
drm/amdgpu: prevent spurious warning
drm/amdgpu/swsmu: fix ARC build errors
drm/amd/display: Fix OPTC_DATA_FORMAT programming
drm/amd/display: Don't allow pstate if no support in blank
drm/panfrost: increase readl_relaxed_poll_timeout values
MAINTAINERS: Update entry for st7703 driver after the rename
Revert "gpu/drm: ingenic: Add option to mmap GEM buffers cached"
drm/amd/display: HDMI remote sink need mode validation for Linux
drm/amd/display: Change to correct unit on audio rate
drm/amd/display: Avoid set zero in the requested clk
drm/amdgpu: align frag_end to covered address space
drm/amdgpu: fix NULL pointer dereference for Renoir
drm/vmwgfx: fix regression in thp code due to ttm init refactor.
drm/amdgpu/swsmu: add interrupt work handler for smu11 parts
drm/amdgpu/swsmu: add interrupt work function
...
Sometimes we have to be very careful not to allocate underneath a mutex
(or spinlock) and yet still want to track activity. Enter
i915_active_acquire_for_context(). This raises the activity counter on
i915_active prior to use and ensures that the fence-tree contains a slot
for the context.
v2: Refactor active_lookup() so it can be called again before/after
locking to resolve contention. Since we protect the rbtree until we
idle, we can do a lockfree lookup, with the caveat that if another
thread performs a concurrent insertion, the rotations from the insert
may cause us to not find our target. A second pass holding the treelock
will find the target if it exists, or the place to perform our
insertion.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Thomas Hellström <thomas.hellstrom@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200731085015.32368-3-chris@chris-wilson.co.uk
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
On Braswell and Broxton (also known as Valleyview and Apollolake), we
need to serialise updates of the GGTT using the big stop_machine()
hammer. This has the side effect of appearing to lockdep as a possible
reclaim (since it uses the cpuhp mutex and that is tainted by per-cpu
allocations). However, we want to use vm->mutex (including ggtt->mutex)
from within the shrinker and so must avoid such possible taints. For this
purpose, we introduced the asynchronous vma binding and we can apply it
to the PIN_GLOBAL so long as take care to add the necessary waits for
the worker afterwards.
Closes: https://gitlab.freedesktop.org/drm/intel/issues/211
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200130181710.2030251-3-chris@chris-wilson.co.uk
As we use a mutex to serialise the first acquire (as it may be a lengthy
operation), but only an atomic decrement for the release, we have to
be careful in case a second thread races and completes both
acquire/release as the first finishes its acquire.
Thread A Thread B
i915_active_acquire i915_active_acquire
atomic_read() == 0 atomic_read() == 0
mutex_lock() mutex_lock()
atomic_read() == 0
ref->active();
atomic_inc()
mutex_unlock()
atomic_read() == 1
i915_active_release
atomic_dec_and_test() -> 0
ref->retire()
atomic_inc() -> 1
mutex_unlock()
So thread A has acquired the ref->active_count but since the ref was
still active at the time, it did not initialise it. By switching the
check inside the mutex to an atomic increment only if already active, we
close the race.
Fixes: c9ad602fea ("drm/i915: Split i915_active.mutex into an irq-safe spinlock for the rbtree")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200126102346.1877661-3-chris@chris-wilson.co.uk
Allocate only an internal intel_context for the kernel_context, forgoing
a global GEM context for internal use as we only require a separate
address space (for our own protection).
Now having weaned GT from requiring ce->gem_context, we can stop
referencing it entirely. This also means we no longer have to create random
and unnecessary GEM contexts for internal use.
GEM contexts are now entirely for tracking GEM clients, and intel_context
the execution environment on the GPU.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Andi Shyti <andi.shyti@intel.com>
Acked-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191221160324.1073045-1-chris@chris-wilson.co.uk
Similar to for i915_active.mutex, we require each class of i915_active
to have distinct lockdep chains as some, but by no means all,
i915_active are used within the shrinker and so have much more severe
usage constraints. By using a lockclass local to i915_active_init() all
i915_active workers have the same lock class, and we may generate false
positives when waiting for the i915_active. If we push the lockclass
into the caller, each class of i915_active will have distinct lockdep
chains.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191202140133.2444217-1-chris@chris-wilson.co.uk
The expected downside to commit 58b4c1a07a ("drm/i915: Reduce nested
prepare_remote_context() to a trylock") was that it would need to return
-EAGAIN to userspace in order to resolve potential mutex inversion. Such
an unsightly round trip is unnecessary if we could atomically insert a
barrier into the i915_active_fence, so make it happen.
Currently, we use the timeline->mutex (or some other named outer lock)
to order insertion into the i915_active_fence (and so individual nodes
of i915_active). Inside __i915_active_fence_set, we only need then
serialise with the interrupt handler in order to claim the timeline for
ourselves.
However, if we remove the outer lock, we need to ensure the order is
intact between not only multiple threads trying to insert themselves
into the timeline, but also with the interrupt handler completing the
previous occupant. We use xchg() on insert so that we have an ordered
sequence of insertions (and each caller knows the previous fence on
which to wait, preserving the chain of all fences in the timeline), but
we then have to cmpxchg() in the interrupt handler to avoid overwriting
the new occupant. The only nasty side-effect is having to temporarily
strip off the RCU-annotations to apply the atomic operations, otherwise
the rules are much more conventional!
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112402
Fixes: 58b4c1a07a ("drm/i915: Reduce nested prepare_remote_context() to a trylock")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191127134527.3438410-1-chris@chris-wilson.co.uk
To flush idle barriers, and even inflight requests, we want to send a
preemptive 'pulse' along an engine. We use a no-op request along the
pinned kernel_context at high priority so that it should run or else
kick off the stuck requests. We can use this to ensure idle barriers are
immediately flushed, as part of a context cancellation mechanism, or as
part of a heartbeat mechanism to detect and reset a stuck GPU.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191021174339.5389-1-chris@chris-wilson.co.uk
Medium term goal is to eliminate the i915->engine[] array and to get there
we have recently introduced equivalent array in intel_gt. Now we need to
migrate the code further towards this state.
This next step is to eliminate usage of i915->engines[] from the
for_each_engine_masked iterator.
For this to work we also need to use engine->id as index when populating
the gt->engine[] array and adjust the default engine set indexing to use
engine->legacy_idx instead of assuming gt->engines[] indexing.
v2:
* Populate gt->engine[] earlier.
* Check that we don't duplicate engine->legacy_idx
v3:
* Work around the initialization order issue between default_engines()
and intel_engines_driver_register() which sets engine->legacy_idx for
now. It will be fixed properly later.
v4:
* Merge with forgotten v2.5.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191017161852.8836-1-tvrtko.ursulin@linux.intel.com
Forgo the struct_mutex serialisation for i915_active, and interpose its
own mutex handling for active/retire.
This is a multi-layered sleight-of-hand. First, we had to ensure that no
active/retire callbacks accidentally inverted the mutex ordering rules,
nor assumed that they were themselves serialised by struct_mutex. More
challenging though, is the rule over updating elements of the active
rbtree. Instead of the whole i915_active now being serialised by
struct_mutex, allocations/rotations of the tree are serialised by the
i915_active.mutex and individual nodes are serialised by the caller
using the i915_timeline.mutex (we need to use nested spinlocks to
interact with the dma_fence callback lists).
The pain point here is that instead of a single mutex around execbuf, we
now have to take a mutex for active tracker (one for each vma, context,
etc) and a couple of spinlocks for each fence update. The improvement in
fine grained locking allowing for multiple concurrent clients
(eventually!) should be worth it in typical loads.
v2: Add some comments that barely elucidate anything :(
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004134015.13204-6-chris@chris-wilson.co.uk
Replace the struct_mutex requirement for pinning the i915_vma with the
local vm->mutex instead. Note that the vm->mutex is tainted by the
shrinker (we require unbinding from inside fs-reclaim) and so we cannot
allocate while holding that mutex. Instead we have to preallocate
workers to do allocate and apply the PTE updates after we have we
reserved their slot in the drm_mm (using fences to order the PTE writes
with the GPU work and with later unbind).
In adding the asynchronous vma binding, one subtle requirement is to
avoid coupling the binding fence into the backing object->resv. That is
the asynchronous binding only applies to the vma timeline itself and not
to the pages as that is a more global timeline (the binding of one vma
does not need to be ordered with another vma, nor does the implicit GEM
fencing depend on a vma, only on writes to the backing store). Keeping
the vma binding distinct from the backing store timelines is verified by
a number of async gem_exec_fence and gem_exec_schedule tests. The way we
do this is quite simple, we keep the fence for the vma binding separate
and only wait on it as required, and never add it to the obj->resv
itself.
Another consequence in reducing the locking around the vma is the
destruction of the vma is no longer globally serialised by struct_mutex.
A natural solution would be to add a kref to i915_vma, but that requires
decoupling the reference cycles, possibly by introducing a new
i915_mm_pages object that is own by both obj->mm and vma->pages.
However, we have not taken that route due to the overshadowing lmem/ttm
discussions, and instead play a series of complicated games with
trylocks to (hopefully) ensure that only one destruction path is called!
v2: Add some commentary, and some helpers to reduce patch churn.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004134015.13204-4-chris@chris-wilson.co.uk
The request->timeline is only valid until the request is retired (i.e.
before it is completed). Upon retiring the request, the context may be
unpinned and freed, and along with it the timeline may be freed. We
therefore need to be very careful when chasing rq->timeline that the
pointer does not disappear beneath us. The vast majority of users are in
a protected context, either during request construction or retirement,
where the timeline->mutex is held and the timeline cannot disappear. It
is those few off the beaten path (where we access a second timeline) that
need extra scrutiny -- to be added in the next patch after first adding
the warnings about dangerous access.
One complication, where we cannot use the timeline->mutex itself, is
during request submission onto hardware (under spinlocks). Here, we want
to check on the timeline to finalize the breadcrumb, and so we need to
impose a second rule to ensure that the request->timeline is indeed
valid. As we are submitting the request, it's context and timeline must
be pinned, as it will be used by the hardware. Since it is pinned, we
know the request->timeline must still be valid, and we cannot submit the
idle barrier until after we release the engine->active.lock, ergo while
submitting and holding that spinlock, a second thread cannot release the
timeline.
v2: Don't be lazy inside selftests; hold the timeline->mutex for as long
as we need it, and tidy up acquiring the timeline with a bit of
refactoring (i915_active_add_request)
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190919111912.21631-1-chris@chris-wilson.co.uk
We use the request pointer inside the i915_active_node as the indicator
of the barrier's status; we mark it as used during
i915_request_add_active_barriers(), and search for an available barrier
in reuse_idle_barrier(). That check must be carefully serialised to
ensure we do use an engine for the barrier and not just a random
pointer. (Along the other reuse path, we are fully serialised by the
timeline->mutex.) The acquisition of the barrier itself is ordered through
the strong memory barrier in llist_del_all().
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111397
Fixes: d8af05ff38 ("drm/i915: Allow sharing the idle-barrier from other kernel requests")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190813200905.11369-1-chris@chris-wilson.co.uk
By placing our idle-barriers in the i915_active fence tree, we expose
those for reuse by other components that are issuing requests along the
kernel_context. Reusing the proto-barrier active_node is perfectly fine
as the new request implies a context-switch, and so an opportune point
to run the idle-barrier. However, the proto-barrier is not equivalent
to a normal active_node and care must be taken to avoid dereferencing the
ERR_PTR used as its request marker.
v2: Comment the more egregious cheek
v3: A glossary!
Reported-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: ce476c80b8 ("drm/i915: Keep contexts pinned until after the next kernel context switch")
Fixes: a9877da2d6 ("drm/i915/oa: Reconfigure contexts on the fly")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190802100015.1281-1-chris@chris-wilson.co.uk
