dma-buf/dma-resv: Add a way to set fence deadline

Add a way to set a deadline on remaining resv fences according to the
requested usage.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Christian König <christian.koenig@amd.com>

dma-buf/dma_resv_usage: update explicit sync documentation

Make it clear that DMA_RESV_USAGE_BOOKKEEP can be used for explicit synced
user space submissions as well and document the rules around adding the
same fence with different usages.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220712131201.131475-1-christian.koenig@amd.com

dma-buf: drop seq count based update

This should be possible now since we don't have the distinction
between exclusive and shared fences any more.

The only possible pitfall is that a dma_fence would be reused during the
RCU grace period, but even that could be handled with a single extra check.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220407085946.744568-15-christian.koenig@amd.com

dma-buf: add DMA_RESV_USAGE_BOOKKEEP v3

Add an usage for submissions independent of implicit sync but still
interesting for memory management.

v2: cleanup the kerneldoc a bit
v3: separate amdgpu changes from this

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220407085946.744568-10-christian.koenig@amd.com

dma-buf: add DMA_RESV_USAGE_KERNEL v3

Add an usage for kernel submissions. Waiting for those are mandatory for
dynamic DMA-bufs.

As a precaution this patch also changes all occurrences where fences are
added as part of memory management in TTM, VMWGFX and i915 to use the
new value because it now becomes possible for drivers to ignore fences
with the WRITE usage.

v2: use "must" in documentation, fix whitespaces
v3: separate out some driver changes and better document why some
changes should still be part of this patch.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220407085946.744568-5-christian.koenig@amd.com

dma-buf & drm/amdgpu: remove dma_resv workaround

Rework the internals of the dma_resv object to allow adding more than one
write fence and remember for each fence what purpose it had.

This allows removing the workaround from amdgpu which used a container for
this instead.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20220407085946.744568-4-christian.koenig@amd.com

dma-buf: specify usage while adding fences to dma_resv obj v7

Instead of distingting between shared and exclusive fences specify
the fence usage while adding fences.

Rework all drivers to use this interface instead and deprecate the old one.

v2: some kerneldoc comments suggested by Daniel
v3: fix a missing case in radeon
v4: rebase on nouveau changes, fix lockdep and temporary disable warning
v5: more documentation updates
v6: separate internal dma_resv changes from this patch, avoids to
disable warning temporary, rebase on upstream changes
v7: fix missed case in lima driver, minimize changes to i915_gem_busy_ioctl

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220407085946.744568-3-christian.koenig@amd.com

dma-buf: add enum dma_resv_usage v4

This change adds the dma_resv_usage enum and allows us to specify why a
dma_resv object is queried for its containing fences.

Additional to that a dma_resv_usage_rw() helper function is added to aid
retrieving the fences for a read or write userspace submission.

This is then deployed to the different query functions of the dma_resv
object and all of their users. When the write paratermer was previously
true we now use DMA_RESV_USAGE_WRITE and DMA_RESV_USAGE_READ otherwise.

v2: add KERNEL/OTHER in separate patch
v3: some kerneldoc suggestions by Daniel
v4: some more kerneldoc suggestions by Daniel, fix missing cases lost in
the rebase pointed out by Bas.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220407085946.744568-2-christian.koenig@amd.com

dma-buf/drivers: make reserving a shared slot mandatory v4

Audit all the users of dma_resv_add_excl_fence() and make sure they
reserve a shared slot also when only trying to add an exclusive fence.

This is the next step towards handling the exclusive fence like a
shared one.

v2: fix missed case in amdgpu
v3: and two more radeon, rename function
v4: add one more case to TTM, fix i915 after rebase

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220406075132.3263-2-christian.koenig@amd.com

dma-buf: finally make dma_resv_excl_fence private v2

Drivers should never touch this directly.

v2: fix rebase clash

Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220321135856.1331-10-christian.koenig@amd.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

dma-buf: add dma_resv_get_singleton v2

Add a function to simplify getting a single fence for all the fences in
the dma_resv object.

v2: fix ref leak in error handling

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220321135856.1331-3-christian.koenig@amd.com

dma-buf: drop the DAG approach for the dma_resv object v3

So far we had the approach of using a directed acyclic
graph with the dma_resv obj.

This turned out to have many downsides, especially it means
that every single driver and user of this interface needs
to be aware of this restriction when adding fences. If the
rules for the DAG are not followed then we end up with
potential hard to debug memory corruption, information
leaks or even elephant big security holes because we allow
userspace to access freed up memory.

Since we already took a step back from that by always
looking at all fences we now go a step further and stop
dropping the shared fences when a new exclusive one is
added.

v2: Drop some now superflous documentation
v3: Add some more documentation for the new handling.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220321135856.1331-11-christian.koenig@amd.com

dma-buf: finally make the dma_resv_list private v2

Drivers should never touch this directly.

v2: drop kerneldoc for now internal handling

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220321135856.1331-2-christian.koenig@amd.com

dma-buf: add dma_resv_replace_fences v2

This function allows to replace fences from the shared fence list when
we can gurantee that the operation represented by the original fence has
finished or no accesses to the resources protected by the dma_resv
object any more when the new fence finishes.

Then use this function in the amdkfd code when BOs are unmapped from the
process.

v2: add an example when this is usefull.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220321135856.1331-1-christian.koenig@amd.com

dma-resv: some doc polish for iterators

Hammer it a bit more in that iterators can be restarted and when that
matters, plus suggest to prefer the locked version whenver.

Also delete the two leftover kerneldoc for static functions plus
sprinkle some more links while at it.

v2: Keep some comments (Christian)

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Link: https://patchwork.freedesktop.org/patch/msgid/20211130152756.1388106-1-daniel.vetter@ffwll.ch

dma-buf: drop excl_fence parameter from dma_resv_get_fences

Returning the exclusive fence separately is no longer used.

Instead add a write parameter to indicate the use case.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20211207123411.167006-4-christian.koenig@amd.com

dma-buf: nuke dma_resv_get_excl_unlocked

Heureka, that's finally not used any more.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210917123513.1106-27-christian.koenig@amd.com

dma-buf: add dma_fence_describe and dma_resv_describe v2

Add functions to dump dma_fence and dma_resv objects into a seq_file and
use them for printing the debugfs information.

v2: fix missing include reported by test robot.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211103081231.18578-2-christian.koenig@amd.com

dma-resv: Fix dma_resv_get_fences and dma_resv_copy_fences after conversion

Cache the count of shared fences in the iterator to avoid dereferencing
the dma_resv_object outside the RCU protection. Otherwise iterator and its
users can observe an incosistent state which makes it impossible to use
safely. Such as:

<6> [187.517041] [IGT] gem_sync: executing
<7> [187.536343] i915 0000:00:02.0: [drm:i915_gem_context_create_ioctl [i915]] HW context 1 created
<7> [187.536793] i915 0000:00:02.0: [drm:i915_gem_context_create_ioctl [i915]] HW context 1 created
<6> [187.551235] [IGT] gem_sync: starting subtest basic-many-each
<1> [188.935462] BUG: kernel NULL pointer dereference, address: 0000000000000010
<1> [188.935485] #PF: supervisor write access in kernel mode
<1> [188.935495] #PF: error_code(0x0002) - not-present page
<6> [188.935504] PGD 0 P4D 0
<4> [188.935512] Oops: 0002 [#1] PREEMPT SMP NOPTI
<4> [188.935521] CPU: 2 PID: 1467 Comm: gem_sync Not tainted 5.15.0-rc4-CI-Patchwork_21264+ #1
<4> [188.935535] Hardware name: /NUC6CAYB, BIOS AYAPLCEL.86A.0049.2018.0508.1356 05/08/2018
<4> [188.935546] RIP: 0010:dma_resv_get_fences+0x116/0x2d0
<4> [188.935560] Code: 10 85 c0 7f c9 be 03 00 00 00 e8 15 8b df ff eb bd e8 8e c6 ff ff eb b6 41 8b 04 24 49 8b 55 00 48 89 e7 8d 48 01 41 89 0c 24 <4c> 89 34 c2 e8 41 f2 ff ff 49 89 c6 48 85 c0 75 8c 48 8b 44 24 10
<4> [188.935583] RSP: 0018:ffffc900011dbcc8 EFLAGS: 00010202
<4> [188.935593] RAX: 0000000000000000 RBX: 00000000ffffffff RCX: 0000000000000001
<4> [188.935603] RDX: 0000000000000010 RSI: ffffffff822e343c RDI: ffffc900011dbcc8
<4> [188.935613] RBP: ffffc900011dbd48 R08: ffff88812d255bb8 R09: 00000000fffffffe
<4> [188.935623] R10: 0000000000000001 R11: 0000000000000000 R12: ffffc900011dbd44
<4> [188.935633] R13: ffffc900011dbd50 R14: ffff888113d29cc0 R15: 0000000000000000
<4> [188.935643] FS: 00007f68d17e9700(0000) GS:ffff888277900000(0000) knlGS:0000000000000000
<4> [188.935655] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
<4> [188.935665] CR2: 0000000000000010 CR3: 000000012d0a4000 CR4: 00000000003506e0
<4> [188.935676] Call Trace:
<4> [188.935685] i915_gem_object_wait+0x1ff/0x410 [i915]
<4> [188.935988] i915_gem_wait_ioctl+0xf2/0x2a0 [i915]
<4> [188.936272] ? i915_gem_object_wait+0x410/0x410 [i915]
<4> [188.936533] drm_ioctl_kernel+0xae/0x140
<4> [188.936546] drm_ioctl+0x201/0x3d0
<4> [188.936555] ? i915_gem_object_wait+0x410/0x410 [i915]
<4> [188.936820] ? __fget_files+0xc2/0x1c0
<4> [188.936830] ? __fget_files+0xda/0x1c0
<4> [188.936839] __x64_sys_ioctl+0x6d/0xa0
<4> [188.936848] do_syscall_64+0x3a/0xb0
<4> [188.936859] entry_SYSCALL_64_after_hwframe+0x44/0xae

If the shared object has changed during the RCU unlocked period
callers will correctly handle the restart on the next iteration.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: 96601e8a4755 ("dma-buf: use new iterator in dma_resv_copy_fences")
Fixes: d3c80698c9f5 ("dma-buf: use new iterator in dma_resv_get_fences v3")
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4274
Cc: Christian König <christian.koenig@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org
Link: https://patchwork.freedesktop.org/patch/msgid/20211008095007.972693-1-tvrtko.ursulin@linux.intel.com
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>

dma-buf: add dma_resv_for_each_fence v3

A simpler version of the iterator to be used when the dma_resv object is
locked.

v2: fix index check here as well
v3: minor coding improvement, some documentation cleanup

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211006123609.2026-1-christian.koenig@amd.com

dma-buf: add dma_resv_for_each_fence_unlocked v8

Abstract the complexity of iterating over all the fences
in a dma_resv object.

The new loop handles the whole RCU and retry dance and
returns only fences where we can be sure we grabbed the
right one.

v2: fix accessing the shared fences while they might be freed,
improve kerneldoc, rename _cursor to _iter, add
dma_resv_iter_is_exclusive, add dma_resv_iter_begin/end

v3: restructor the code, move rcu_read_lock()/unlock() into the
iterator, add dma_resv_iter_is_restarted()

v4: fix NULL deref when no explicit fence exists, drop superflous
rcu_read_lock()/unlock() calls.

v5: fix typos in the documentation

v6: fix coding error when excl fence is NULL

v7: one more logic fix

v8: fix index check in dma_resv_iter_is_exclusive()

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> (v7)
Link: https://patchwork.freedesktop.org/patch/msgid/20211005113742.1101-2-christian.koenig@amd.com

dma-resv: Give the docs a do-over

Specifically document the new/clarified rules around how the shared
fences do not have any ordering requirements against the exclusive
fence.

But also document all the things a bit better, given how central
struct dma_resv to dynamic buffer management the docs have been very
inadequat.

- Lots more links to other pieces of the puzzle. Unfortunately
ttm_buffer_object has no docs, so no links :-(

- Explain/complain a bit about dma_resv_locking_ctx(). I still don't
like that one, but fixing the ttm call chains is going to be
horrible. Plus we want to plug in real slowpath locking when we do
that anyway.

- Main part of the patch is some actual docs for struct dma_resv.

Overall I think we still have a lot of bad naming in this area (e.g.
dma_resv.fence is singular, but contains the multiple shared fences),
but I think that's more indicative of how the semantics and rules are
just not great.

Another thing that's real awkard is how chaining exclusive fences
right now means direct dma_resv.exclusive_fence pointer access with an
rcu_assign_pointer. Not so great either.

v2:
- Fix a pile of typos (Matt, Jason)
- Hammer it in that breaking the rules leads to use-after-free issues
around dma-buf sharing (Christian)

Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Link: https://patchwork.freedesktop.org/patch/msgid/20210805104705.862416-21-daniel.vetter@ffwll.ch

kernel/locking: Add context to ww_mutex_trylock()

i915 will soon gain an eviction path that trylock a whole lot of locks
for eviction, getting dmesg failures like below:

BUG: MAX_LOCK_DEPTH too low!
turning off the locking correctness validator.
depth: 48 max: 48!
48 locks held by i915_selftest/5776:
#0: ffff888101a79240 (&dev->mutex){....}-{3:3}, at: __driver_attach+0x88/0x160
#1: ffffc900009778c0 (reservation_ww_class_acquire){+.+.}-{0:0}, at: i915_vma_pin.constprop.63+0x39/0x1b0 [i915]
#2: ffff88800cf74de8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_vma_pin.constprop.63+0x5f/0x1b0 [i915]
#3: ffff88810c7f9e38 (&vm->mutex/1){+.+.}-{3:3}, at: i915_vma_pin_ww+0x1c4/0x9d0 [i915]
#4: ffff88810bad5768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
#5: ffff88810bad60e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
...
#46: ffff88811964d768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
#47: ffff88811964e0e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
INFO: lockdep is turned off.

Fixing eviction to nest into ww_class_acquire is a high priority, but
it requires a rework of the entire driver, which can only be done one
step at a time.

As an intermediate solution, add an acquire context to
ww_mutex_trylock, which allows us to do proper nesting annotations on
the trylocks, making the above lockdep splat disappear.

This is also useful in regulator_lock_nested, which may avoid dropping
regulator_nesting_mutex in the uncontended path, so use it there.

TTM may be another user for this, where we could lock a buffer in a
fastpath with list locks held, without dropping all locks we hold.

[peterz: rework actual ww_mutex_trylock() implementations]
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/YUBGPdDDjKlxAuXJ@hirez.programming.kicks-ass.net

dma-resv: Fix kerneldoc

Oversight from

commit 6edbd6abb783d54f6ac4c3ed5cd9e50cff6c15e9
Author: Christian König <christian.koenig@amd.com>
Date: Mon May 10 16:14:09 2021 +0200

dma-buf: rename and cleanup dma_resv_get_excl v3

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Link: https://patchwork.freedesktop.org/patch/msgid/20210622165511.3169559-2-daniel.vetter@ffwll.ch

<linux/dma-resv.h>: correct a function name in kernel-doc

Fix kernel-doc function name warning:

../include/linux/dma-resv.h:227: warning: expecting prototype for dma_resv_exclusive(). Prototype was for dma_resv_excl_fence() instead

Fixes: 6edbd6abb783d ("dma-buf: rename and cleanup dma_resv_get_excl v3")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Christian König <christian.koenig@amd.com>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210628004012.6792-1-rdunlap@infradead.org

dma-buf: drop the _rcu postfix on function names v3

The functions can be called both in _rcu context as well
as while holding the lock.

v2: add some kerneldoc as suggested by Daniel
v3: fix indentation

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210602111714.212426-7-christian.koenig@amd.com

dma-buf: rename dma_resv_get_excl_rcu to _unlocked

That describes much better what the function is doing here.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210602111714.212426-6-christian.koenig@amd.com

dma-buf: rename and cleanup dma_resv_get_list v2

When the comment needs to state explicitly that this is doesn't get a reference
to the object then the function is named rather badly.

Rename the function and use it in even more places.

v2: use dma_resv_shared_list as new name

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210602111714.212426-5-christian.koenig@amd.com

dma-buf: rename and cleanup dma_resv_get_excl v3

When the comment needs to state explicitly that this
doesn't get a reference to the object then the function
is named rather badly.

Rename the function and use rcu_dereference_check(), this
way it can be used from both rcu as well as lock protected
critical sections.

v2: improve kerneldoc as suggested by Daniel
v3: use dma_resv_excl_fence as function name

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20210602111714.212426-4-christian.koenig@amd.com

dma-buf: cleanup dma-resv shared fence debugging a bit v2

Make that a function instead of inline.

v2: improve the kerneldoc wording as suggested by Daniel

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210602111714.212426-3-christian.koenig@amd.com

dma-buf: Use sequence counter with associated wound/wait mutex

A sequence counter write side critical section must be protected by some
form of locking to serialize writers. If the serialization primitive is
not disabling preemption implicitly, preemption has to be explicitly
disabled before entering the sequence counter write side critical
section.

The dma-buf reservation subsystem uses plain sequence counters to manage
updates to reservations. Writer serialization is accomplished through a
wound/wait mutex.

Acquiring a wound/wait mutex does not disable preemption, so this needs
to be done manually before and after the write side critical section.

Use the newly-added seqcount_ww_mutex_t instead:

- It associates the ww_mutex with the sequence count, which enables
lockdep to validate that the write side critical section is properly
serialized.

- It removes the need to explicitly add preempt_disable/enable()
around the write side critical section because the write_begin/end()
functions for this new data type automatically do this.

If lockdep is disabled this ww_mutex lock association is compiled out
and has neither storage size nor runtime overhead.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://lkml.kernel.org/r/20200720155530.1173732-13-a.darwish@linutronix.de

dma-buf: Remove custom seqcount lockdep class key

Commit 3c3b177a9369 ("reservation: add support for read-only access
using rcu") introduced a sequence counter to manage updates to
reservations. Back then, the reservation object initializer
reservation_object_init() was always inlined.

Having the sequence counter initialization inlined meant that each of
the call sites would have a different lockdep class key, which would've
broken lockdep's deadlock detection. The aforementioned commit thus
introduced, and exported, a custom seqcount lockdep class key and name.

The commit 8735f16803f00 ("dma-buf: cleanup reservation_object_init...")
transformed the reservation object initializer to a normal non-inlined C
function. seqcount_init(), which automatically defines the seqcount
lockdep class key and must be called non-inlined, can now be safely used.

Remove the seqcount custom lockdep class key, name, and export. Use
seqcount_init() inside the dma reservation object initializer.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://lkml.kernel.org/r/20200720155530.1173732-12-a.darwish@linutronix.de

dma-buf: Restore seqlock around dma_resv updates

This reverts
67c97fb79a7f ("dma-buf: add reservation_object_fences helper")
dd7a7d1ff2f1 ("drm/i915: use new reservation_object_fences helper")
0e1d8083bddb ("dma-buf: further relax reservation_object_add_shared_fence")
5d344f58da76 ("dma-buf: nuke reservation_object seq number")

The scenario that defeats simply grabbing a set of shared/exclusive
fences and using them blissfully under RCU is that any of those fences
may be reallocated by a SLAB_TYPESAFE_BY_RCU fence slab cache. In this
scenario, while keeping the rcu_read_lock we need to establish that no
fence was changed in the dma_resv after a read (or full) memory barrier.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190814182401.25009-1-chris@chris-wilson.co.uk

dma-buf: rename reservation_object to dma_resv

Be more consistent with the naming of the other DMA-buf objects.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/323401/