Commit Graph

25 Commits

Author SHA1 Message Date
Christian König
64a8f92fd7 dma-buf: add dma_fence_unwrap v2
Add a general purpose helper to deep dive into dma_fence_chain/dma_fence_array
structures and iterate over all the fences in them.

This is useful when we need to flatten out all fences in those structures.

v2: some selftests cleanup, improved function naming and documentation

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220311110244.1245-1-christian.koenig@amd.com
2022-03-25 14:18:28 +01:00
Lucas De Marchi
7938f42181 dma-buf-map: Rename to iosys-map
Rename struct dma_buf_map to struct iosys_map and corresponding APIs.
Over time dma-buf-map grew up to more functionality than the one used by
dma-buf: in fact it's just a shim layer to abstract system memory, that
can be accessed via regular load and store, from IO memory that needs to
be acessed via arch helpers.

The idea is to extend this API so it can fulfill other needs, internal
to a single driver. Example: in the i915 driver it's desired to share
the implementation for integrated graphics, which uses mostly system
memory, with discrete graphics, which may need to access IO memory.

The conversion was mostly done with the following semantic patch:

	@r1@
	@@
	- struct dma_buf_map
	+ struct iosys_map

	@r2@
	@@
	(
	- DMA_BUF_MAP_INIT_VADDR
	+ IOSYS_MAP_INIT_VADDR
	|
	- dma_buf_map_set_vaddr
	+ iosys_map_set_vaddr
	|
	- dma_buf_map_set_vaddr_iomem
	+ iosys_map_set_vaddr_iomem
	|
	- dma_buf_map_is_equal
	+ iosys_map_is_equal
	|
	- dma_buf_map_is_null
	+ iosys_map_is_null
	|
	- dma_buf_map_is_set
	+ iosys_map_is_set
	|
	- dma_buf_map_clear
	+ iosys_map_clear
	|
	- dma_buf_map_memcpy_to
	+ iosys_map_memcpy_to
	|
	- dma_buf_map_incr
	+ iosys_map_incr
	)

	@@
	@@
	- #include <linux/dma-buf-map.h>
	+ #include <linux/iosys-map.h>

Then some files had their includes adjusted and some comments were
update to remove mentions to dma-buf-map.

Since this is not specific to dma-buf anymore, move the documentation to
the "Bus-Independent Device Accesses" section.

v2:
  - Squash patches

v3:
  - Fix wrong removal of dma-buf.h from MAINTAINERS
  - Move documentation from dma-buf.rst to device-io.rst

v4:
  - Change documentation title and level

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220204170541.829227-1-lucas.demarchi@intel.com
2022-02-07 16:35:35 -08:00
Christian König
cba3ae8b32 dma-buf: cleanup kerneldoc of removed component
The seqno-fence was removed, cleanup the kerneldoc include as well.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Fixes: 992c238188 ("dma-buf: nuke seqno-fence")
Link: https://patchwork.freedesktop.org/patch/msgid/20210901080002.5892-1-christian.koenig@amd.com
2021-09-02 13:14:40 +02:00
Jason Ekstrand
51f52547df dma-buf: Document DMA_BUF_IOCTL_SYNC (v3)
This adds a new "DMA Buffer ioctls" section to the dma-buf docs and adds
documentation for DMA_BUF_IOCTL_SYNC.

v2 (Daniel Vetter):
 - Fix a couple typos
 - Add commentary about synchronization with other devices
 - Use item list format for describing flags

v3 (Pekka Paalanen):
 - Clarify stalling requirements.
 - Be more clear that that DMA_BUF_IOCTL_SYNC with SINC_END has to be
   called before more GPU work happens.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210617194258.579011-1-jason@jlekstrand.net
2021-06-17 21:46:37 +02:00
Hridya Valsaraju
bdb8d06dfe dmabuf: Add the capability to expose DMA-BUF stats in sysfs
Overview
========
The patch adds DMA-BUF statistics to /sys/kernel/dmabuf/buffers. It
allows statistics to be enabled for each DMA-BUF in sysfs by enabling
the config CONFIG_DMABUF_SYSFS_STATS.

The following stats will be exposed by the interface:

/sys/kernel/dmabuf/buffers/<inode_number>/exporter_name
/sys/kernel/dmabuf/buffers/<inode_number>/size
/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/device
/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/map_counter

The inode_number is unique for each DMA-BUF and was added earlier [1]
in order to allow userspace to track DMA-BUF usage across different
processes.

Use Cases
=========
The interface provides a way to gather DMA-BUF per-buffer statistics
from production devices. These statistics will be used to derive DMA-BUF
per-exporter stats and per-device usage stats for Android Bug reports.
The corresponding userspace changes can be found at [2].
Telemetry tools will also capture this information(along with other
memory metrics) periodically as well as on important events like a
foreground app kill (which might have been triggered by Low Memory
Killer). It will also contribute to provide a snapshot of the system
memory usage on other events such as OOM kills and Application Not
Responding events.

Background
==========
Currently, there are two existing interfaces that provide information
about DMA-BUFs.
1) /sys/kernel/debug/dma_buf/bufinfo
debugfs is however unsuitable to be mounted in production systems and
cannot be considered as an alternative to the sysfs interface being
proposed.
2) proc/<pid>/fdinfo/<fd>
The proc/<pid>/fdinfo/<fd> files expose information about DMA-BUF fds.
However, the existing procfs interfaces can only provide information
about the buffers for which processes hold fds or have the buffers
mmapped into their address space. Since the procfs interfaces alone
cannot provide a full picture of all DMA-BUFs in the system, there is
the need for an alternate interface to provide this information on
production systems.

The patch contains the following major improvements over v1:
1) Each attachment is represented by its own directory to allow creating
a symlink to the importing device and to also provide room for future
expansion.
2) The number of distinct mappings of each attachment is exposed in a
separate file.
3) The per-buffer statistics are now in /sys/kernel/dmabuf/buffers
inorder to make the interface expandable in future.

All of the improvements above are based on suggestions/feedback from
Daniel Vetter and Christian König.

A shell script that can be run on a classic Linux environment to read
out the DMA-BUF statistics can be found at [3](suggested by John
Stultz).

[1]: https://lore.kernel.org/patchwork/patch/1088791/
[2]: https://android-review.googlesource.com/q/topic:%22dmabuf-sysfs%22+(status:open%20OR%20status:merged)
[3]: https://android-review.googlesource.com/c/platform/system/memory/libmeminfo/+/1549734

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Hridya Valsaraju <hridya@google.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210603214758.2955251-1-hridya@google.com
2021-06-15 11:50:24 +02:00
Daniel Vetter
b970b8e9fb drm/doc: Include fence chain api
We have this nice kerneldoc, but forgot to include it.

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/20210521082457.1656333-1-daniel.vetter@ffwll.ch
2021-06-03 10:32:49 +02:00
Daniel Vetter
8613385cb2 dma-fence: Document recoverable page fault implications
Recently there was a fairly long thread about recoreable hardware page
faults, how they can deadlock, and what to do about that.

While the discussion is still fresh I figured good time to try and
document the conclusions a bit. This documentation section explains
what's the potential problem, and the remedies we've discussed,
roughly ordered from best to worst.

v2: Linus -> Linux typoe (Dave)

v3:
- Make it clear drivers only need to implement one option (Christian)
- Make it clearer that implicit sync is out the window with exclusive
  fences (Christian)
- Add the fairly theoretical option of segementing the memory (either
  statically or through dynamic checks at runtime for which piece of
  memory is managed how) and explain why it's not a great idea (Felix)

References: https://lore.kernel.org/dri-devel/20210107030127.20393-1-Felix.Kuehling@amd.com/
Reviewed-by: Christian König <christian.koenig@amd.com>
Acked-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
c: Dave Airlie <airlied@gmail.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Thomas Hellström <thomas.hellstrom@intel.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Link: https://patchwork.freedesktop.org/patch/msgid/20210203152921.2429937-1-daniel.vetter@ffwll.ch
2021-03-12 15:10:03 +01:00
Daniel Vetter
26e08a6da5 dma-buf: Fix kerneldoc formatting
I wanted to look up something and noticed the hyperlink doesn't work.
While fixing that also noticed a trivial kerneldoc comment typo in the
same section, fix that too.

Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Reviewed-by: Simon Ser <contact@emersion.fr>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201204200242.2671481-1-daniel.vetter@ffwll.ch
2020-12-11 17:16:55 +01:00
Maxime Ripard
c489573b5b
Merge drm/drm-next into drm-misc-next
Daniel needs -rc2 in drm-misc-next to merge some patches

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
2020-11-02 11:17:54 +01:00
Linus Torvalds
50d228345a As hoped, things calmed down for docs this cycle; fewer changes and almost
no conflicts at all.  This pull includes:
 
  - A reworked and expanded user-mode Linux document
  - Some simplifications and improvements for submitting-patches.rst
  - An emergency fix for (some) problems with Sphinx 3.x
  - Some welcome automarkup improvements to automatically generate
    cross-references to struct definitions and other documents
  - The usual collection of translation updates, typo fixes, etc.
 -----BEGIN PGP SIGNATURE-----
 
 iQFDBAABCAAtFiEEIw+MvkEiF49krdp9F0NaE2wMflgFAl+ErNYPHGNvcmJldEBs
 d24ubmV0AAoJEBdDWhNsDH5Y284H/3bv9fahbg16AJcKYqJXFHGpDs3CsASPnJqQ
 9HQoV5tg6Qd4kI3oFb+30l8SK73Wr2t685/DhOPDRR/vN3B5M1vOQvPRL/dEqiwi
 aUEhtMbnC/trSbteXsjGDWT+1EnI/+R3NFV++WiRp1XxE4DRXL3xySTeviR0IW+V
 rQxU7VCcVp0bklVH+gqjrsvqU5iZeckyZB6evc8X92ThhzjNprR5KVxxgl1wxcu/
 dPYizHoKYVoLVNw50rwPGt2hmq9RpyDM6Xh9UhLHcA57ENyzr8NNTJBOT0tVMTWV
 smU01X/ECoy54kj1w8AKP+f7F0G7DUU+Jz68X0X/kYPq520dUs4=
 =Ovox
 -----END PGP SIGNATURE-----

Merge tag 'docs-5.10' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "As hoped, things calmed down for docs this cycle; fewer changes and
  almost no conflicts at all. This includes:

   - A reworked and expanded user-mode Linux document

   - Some simplifications and improvements for submitting-patches.rst

   - An emergency fix for (some) problems with Sphinx 3.x

   - Some welcome automarkup improvements to automatically generate
     cross-references to struct definitions and other documents

   - The usual collection of translation updates, typo fixes, etc"

* tag 'docs-5.10' of git://git.lwn.net/linux: (81 commits)
  gpiolib: Update indentation in driver.rst for code excerpts
  Documentation/admin-guide: tainted-kernels: Fix typo occured
  Documentation: better locations for sysfs-pci, sysfs-tagging
  docs: programming-languages: refresh blurb on clang support
  Documentation: kvm: fix a typo
  Documentation: Chinese translation of Documentation/arm64/amu.rst
  doc: zh_CN: index files in arm64 subdirectory
  mailmap: add entry for <mstarovoitov@marvell.com>
  doc: seq_file: clarify role of *pos in ->next()
  docs: trace: ring-buffer-design.rst: use the new SPDX tag
  Documentation: kernel-parameters: clarify "module." parameters
  Fix references to nommu-mmap.rst
  docs: rewrite admin-guide/sysctl/abi.rst
  docs: fb: Remove vesafb scrollback boot option
  docs: fb: Remove sstfb scrollback boot option
  docs: fb: Remove matroxfb scrollback boot option
  docs: fb: Remove framebuffer scrollback boot option
  docs: replace the old User Mode Linux HowTo with a new one
  Documentation/admin-guide: blockdev/ramdisk: remove use of "rdev"
  Documentation/admin-guide: README & svga: remove use of "rdev"
  ...
2020-10-12 16:21:29 -07:00
Thomas Zimmermann
ccc22d41bd dma-buf: Document struct dma_buf_map
This patch adds struct dma_buf_map and its helpers to the documentation. A
short tutorial is included.

v3:
	* update documentation in a separate patch
	* expand docs (Daniel)
	* carry-over acks from patch 1

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200925115601.23955-5-tzimmermann@suse.de
2020-09-29 12:41:27 +02:00
Mauro Carvalho Chehab
b899353d22 docs: dma-buf: fix some warnings
Fix those warnings:

	Documentation/driver-api/dma-buf.rst:182: WARNING: Title underline too short.

	Indefinite DMA Fences
	~~~~~~~~~~~~~~~~~~~~

	Documentation/driver-api/dma-buf.rst:88: WARNING: Unknown target name: "fence poll support".

The first one is due to a shorter markup. The second one is
because the chapter name was wrong.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/b2bc0bc88eb913635cfece13cc9f6eff7668d333.1599660067.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2020-09-10 10:49:43 -06:00
Randy Dunlap
6546d28f0e Documentation: fix dma-buf.rst underline length warning
/home/rdunlap/lnx/lnx-59-rc2/Documentation/driver-api/dma-buf.rst:182: WARNING: Title underline too short.
Indefinite DMA Fences
~~~~~~~~~~~~~~~~~~~~

Fixes: 72b6ede736 ("dma-buf.rst: Document why indefinite fences are a bad idea")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Dave Airlie <airlied@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1b22d4c3-4ea5-c633-9e35-71ce65d8dbcc@infradead.org
2020-09-01 09:59:53 +02:00
Daniel Vetter
72b6ede736 dma-buf.rst: Document why indefinite fences are a bad idea
Comes up every few years, gets somewhat tedious to discuss, let's
write this down once and for all.

What I'm not sure about is whether the text should be more explicit in
flat out mandating the amdkfd eviction fences for long running compute
workloads or workloads where userspace fencing is allowed.

v2: Now with dot graph!

v3: Typo (Dave Airlie)

Reviewed-by: Thomas Hellstrom <thomas.hellstrom@intel.com>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Jesse Natalie <jenatali@microsoft.com>
Cc: Steve Pronovost <spronovo@microsoft.com>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Thomas Hellstrom <thomas.hellstrom@intel.com>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Cc: linux-rdma@vger.kernel.org
Cc: amd-gfx@lists.freedesktop.org
Cc: intel-gfx@lists.freedesktop.org
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200709123339.547390-1-daniel.vetter@ffwll.ch
2020-07-21 09:42:19 +02:00
Daniel Vetter
d0b9a9aef0 dma-fence: prime lockdep annotations
Two in one go:
- it is allowed to call dma_fence_wait() while holding a
  dma_resv_lock(). This is fundamental to how eviction works with ttm,
  so required.

- it is allowed to call dma_fence_wait() from memory reclaim contexts,
  specifically from shrinker callbacks (which i915 does), and from mmu
  notifier callbacks (which amdgpu does, and which i915 sometimes also
  does, and probably always should, but that's kinda a debate). Also
  for stuff like HMM we really need to be able to do this, or things
  get real dicey.

Consequence is that any critical path necessary to get to a
dma_fence_signal for a fence must never a) call dma_resv_lock nor b)
allocate memory with GFP_KERNEL. Also by implication of
dma_resv_lock(), no userspace faulting allowed. That's some supremely
obnoxious limitations, which is why we need to sprinkle the right
annotations to all relevant paths.

The one big locking context we're leaving out here is mmu notifiers,
added in

commit 23b68395c7
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Mon Aug 26 22:14:21 2019 +0200

    mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end

that one covers a lot of other callsites, and it's also allowed to
wait on dma-fences from mmu notifiers. But there's no ready-made
functions exposed to prime this, so I've left it out for now.

v2: Also track against mmu notifier context.

v3: kerneldoc to spec the cross-driver contract. Note that currently
i915 throws in a hard-coded 10s timeout on foreign fences (not sure
why that was done, but it's there), which is why that rule is worded
with SHOULD instead of MUST.

Also some of the mmu_notifier/shrinker rules might surprise SoC
drivers, I haven't fully audited them all. Which is infeasible anyway,
we'll need to run them with lockdep and dma-fence annotations and see
what goes boom.

v4: A spelling fix from Mika

v5: #ifdef for CONFIG_MMU_NOTIFIER. Reported by 0day. Unfortunately
this means lockdep enforcement is slightly inconsistent, it won't spot
GFP_NOIO and GFP_NOFS allocations in the wrong spot if
CONFIG_MMU_NOTIFIER is disabled in the kernel config. Oh well.

v5: Note that only drivers/gpu has a reasonable (or at least
historical) excuse to use dma_fence_wait() from shrinker and mmu
notifier callbacks. Everyone else should either have a better memory
manager model, or better hardware. This reflects discussions with
Jason Gunthorpe.

Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: kernel test robot <lkp@intel.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@intel.com> (v4)
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Thomas Hellstrom <thomas.hellstrom@intel.com>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Cc: linux-rdma@vger.kernel.org
Cc: amd-gfx@lists.freedesktop.org
Cc: intel-gfx@lists.freedesktop.org
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200707201229.472834-3-daniel.vetter@ffwll.ch
2020-07-21 09:42:19 +02:00
Daniel Vetter
5fbff813a4 dma-fence: basic lockdep annotations
Design is similar to the lockdep annotations for workers, but with
some twists:

- We use a read-lock for the execution/worker/completion side, so that
  this explicit annotation can be more liberally sprinkled around.
  With read locks lockdep isn't going to complain if the read-side
  isn't nested the same way under all circumstances, so ABBA deadlocks
  are ok. Which they are, since this is an annotation only.

- We're using non-recursive lockdep read lock mode, since in recursive
  read lock mode lockdep does not catch read side hazards. And we
  _very_ much want read side hazards to be caught. For full details of
  this limitation see

  commit e914985897
  Author: Peter Zijlstra <peterz@infradead.org>
  Date:   Wed Aug 23 13:13:11 2017 +0200

      locking/lockdep/selftests: Add mixed read-write ABBA tests

- To allow nesting of the read-side explicit annotations we explicitly
  keep track of the nesting. lock_is_held() allows us to do that.

- The wait-side annotation is a write lock, and entirely done within
  dma_fence_wait() for everyone by default.

- To be able to freely annotate helper functions I want to make it ok
  to call dma_fence_begin/end_signalling from soft/hardirq context.
  First attempt was using the hardirq locking context for the write
  side in lockdep, but this forces all normal spinlocks nested within
  dma_fence_begin/end_signalling to be spinlocks. That bollocks.

  The approach now is to simple check in_atomic(), and for these cases
  entirely rely on the might_sleep() check in dma_fence_wait(). That
  will catch any wrong nesting against spinlocks from soft/hardirq
  contexts.

The idea here is that every code path that's critical for eventually
signalling a dma_fence should be annotated with
dma_fence_begin/end_signalling. The annotation ideally starts right
after a dma_fence is published (added to a dma_resv, exposed as a
sync_file fd, attached to a drm_syncobj fd, or anything else that
makes the dma_fence visible to other kernel threads), up to and
including the dma_fence_wait(). Examples are irq handlers, the
scheduler rt threads, the tail of execbuf (after the corresponding
fences are visible), any workers that end up signalling dma_fences and
really anything else. Not annotated should be code paths that only
complete fences opportunistically as the gpu progresses, like e.g.
shrinker/eviction code.

The main class of deadlocks this is supposed to catch are:

Thread A:

	mutex_lock(A);
	mutex_unlock(A);

	dma_fence_signal();

Thread B:

	mutex_lock(A);
	dma_fence_wait();
	mutex_unlock(A);

Thread B is blocked on A signalling the fence, but A never gets around
to that because it cannot acquire the lock A.

Note that dma_fence_wait() is allowed to be nested within
dma_fence_begin/end_signalling sections. To allow this to happen the
read lock needs to be upgraded to a write lock, which means that any
other lock is acquired between the dma_fence_begin_signalling() call and
the call to dma_fence_wait(), and still held, this will result in an
immediate lockdep complaint. The only other option would be to not
annotate such calls, defeating the point. Therefore these annotations
cannot be sprinkled over the code entirely mindless to avoid false
positives.

Originally I hope that the cross-release lockdep extensions would
alleviate the need for explicit annotations:

https://lwn.net/Articles/709849/

But there's a few reasons why that's not an option:

- It's not happening in upstream, since it got reverted due to too
  many false positives:

	commit e966eaeeb6
	Author: Ingo Molnar <mingo@kernel.org>
	Date:   Tue Dec 12 12:31:16 2017 +0100

	    locking/lockdep: Remove the cross-release locking checks

	    This code (CONFIG_LOCKDEP_CROSSRELEASE=y and CONFIG_LOCKDEP_COMPLETIONS=y),
	    while it found a number of old bugs initially, was also causing too many
	    false positives that caused people to disable lockdep - which is arguably
	    a worse overall outcome.

- cross-release uses the complete() call to annotate the end of
  critical sections, for dma_fence that would be dma_fence_signal().
  But we do not want all dma_fence_signal() calls to be treated as
  critical, since many are opportunistic cleanup of gpu requests. If
  these get stuck there's still the main completion interrupt and
  workers who can unblock everyone. Automatically annotating all
  dma_fence_signal() calls would hence cause false positives.

- cross-release had some educated guesses for when a critical section
  starts, like fresh syscall or fresh work callback. This would again
  cause false positives without explicit annotations, since for
  dma_fence the critical sections only starts when we publish a fence.

- Furthermore there can be cases where a thread never does a
  dma_fence_signal, but is still critical for reaching completion of
  fences. One example would be a scheduler kthread which picks up jobs
  and pushes them into hardware, where the interrupt handler or
  another completion thread calls dma_fence_signal(). But if the
  scheduler thread hangs, then all the fences hang, hence we need to
  manually annotate it. cross-release aimed to solve this by chaining
  cross-release dependencies, but the dependency from scheduler thread
  to the completion interrupt handler goes through hw where
  cross-release code can't observe it.

In short, without manual annotations and careful review of the start
and end of critical sections, cross-relese dependency tracking doesn't
work. We need explicit annotations.

v2: handle soft/hardirq ctx better against write side and dont forget
EXPORT_SYMBOL, drivers can't use this otherwise.

v3: Kerneldoc.

v4: Some spelling fixes from Mika

v5: Amend commit message to explain in detail why cross-release isn't
the solution.

v6: Pull out misplaced .rst hunk.

Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Thomas Hellstrom <thomas.hellstrom@intel.com>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Cc: linux-rdma@vger.kernel.org
Cc: amd-gfx@lists.freedesktop.org
Cc: intel-gfx@lists.freedesktop.org
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200707201229.472834-2-daniel.vetter@ffwll.ch
2020-07-21 09:42:19 +02:00
Daniel Vetter
102514ec73 dma-buf: minor doc touch-ups
Just some tiny edits:
- fix link to struct dma_fence
- give slightly more meaningful title - the polling here is about
  implicit fences, explicit fences (in sync_file or drm_syncobj) also
  have their own polling

v2: I misplaced the .rst include change corresponding to this patch.

Reviewed-by: Thomas Hellstrom <thomas.hellstrom@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200612070535.1778368-1-daniel.vetter@ffwll.ch
2020-06-24 16:44:08 +02:00
Gal Pressman
776d58823a dma-buf: Couple of documentation typo fixes
Fix a couple of typos: "as" -> "has" and "int" -> "in".

Signed-off-by: Gal Pressman <galpress@amazon.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200420074115.23931-1-galpress@amazon.com
2020-04-21 14:37:51 +02:00
Anna Karas
0f54621701 doc: drm: Update references to previously renamed files
Update references to reservation.c and reservation.h since these files
have been renamed to dma-resv.c and dma-resv.h respectively.

Cc: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/323401/?series=65037&rev=1
Signed-off-by: Anna Karas <anna.karas@intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190927111504.20136-1-anna.karas@intel.com
2019-10-25 12:46:32 +01:00
Daniel Vetter
4dd3cdb281 dma-fence: Polish kernel-doc for dma-fence.c
- Intro section that links to how this is exposed to userspace.
- Lots more hyperlinks.
- Minor clarifications and style polish

v2: Add misplaced hunk of kerneldoc from a different patch.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Link: https://patchwork.freedesktop.org/patch/msgid/20180704092909.6599-6-daniel.vetter@ffwll.ch
2018-07-04 12:18:37 +02:00
Jonathan Corbet
9b158d860f docs: Do not include from .../seqno-fence.c
There are no kerneldoc comments in drivers/dma-buf/seqno-fence.c, and it
appears there never have been.  Stop looking for comments there to
eliminate this warning:

    ./drivers/dma-buf/seqno-fence.c:1: warning: no structured comments found

Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2017-07-17 14:07:49 -06:00
Daniel Vetter
e7e21c72b1 dma-buf: Final bits of doc polish
- Put all the remaing bits of the old doc into suitable places in the
  new sphinx world.
- Also document the poll support, we forgot to do that.
- Delete dma-buf-sharing.txt.

v2: Don't forget to update MAINTAINERS.

Cc: linux-doc@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20161209215055.3492-1-daniel.vetter@ffwll.ch
2016-12-13 17:54:28 +05:30
Daniel Vetter
0959a1683d dma-buf: Update cpu access documentation
- Again move the information relevant for driver writers next to the
  callbacks.
- Put the overview and userspace interface documentation into a DOC:
  section within the code.
- Remove the text that mmap needs to be coherent - since the
  DMA_BUF_IOCTL_SYNC landed that's no longer the case. But keep the text
  that for pte zapping exporters need to adjust the address space.
- Add a FIXME that kmap and the new begin/end stuff used by the SYNC
  ioctl don't really mix correctly. That's something I just realized
  while doing this doc rework.
- Augment function and structure docs like usual.

Cc: linux-doc@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
  [sumits: fix cosmetic issues]
Link: http://patchwork.freedesktop.org/patch/msgid/20161209185309.1682-5-daniel.vetter@ffwll.ch
2016-12-13 17:53:32 +05:30
Daniel Vetter
2904a8c131 dma-buf: Reorganize device dma access docs
- Put the initial overview for dma-buf into dma-buf.rst.
- Put all the comments about detailed semantics into the right
  kernel-doc comment for functions or ops structure member.
- To allow that detail, switch the reworked kerneldoc to inline style
  for dma_buf_ops.
- Tie everything together into a much more streamlined overview
  comment, relying on the hyperlinks for all the details.
- Also sprinkle some links into the kerneldoc for dma_buf and
  dma_buf_attachment to tie it all together.

Cc: linux-doc@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20161209185309.1682-4-daniel.vetter@ffwll.ch
2016-12-13 17:09:51 +05:30
Daniel Vetter
868c97a846 dma-buf: Extract dma-buf.rst
Just prep work to polish and consolidate all the dma-buf related
documenation.

Unfortunately I didn't discover a way to both integrate this new file
into the overall toc while keeping it at the current place. Work
around that by moving it into the overall driver-api/index.rst.

Cc: linux-doc@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2016-12-11 13:37:55 -07:00