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From: Alex Constantino <dreaming.about.electric.sheep@gmail.com>
To: mripard@kernel.org
Cc: 1054514@bugs.debian.org,
	airlied@redhat.com,
	carnil@debian.org,
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	timo.lindfors@iki.fi,
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Subject: [PATCH v2 0/1] Revert "drm/qxl: simplify qxl_fence_wait"
Date: Thu,  4 Apr 2024 19:14:47 +0100
Message-Id: <20240404181448.1643-1-dreaming.about.electric.sheep@gmail.com>
In-Reply-To: <20240327-cuddly-smooth-trogon-59c02d@houat>
References: <20240327-cuddly-smooth-trogon-59c02d@houat>
Precedence: bulk
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Changes since v1:
- replace new code logic in v1 with past code version by reverting
  commit 5a838e5d5825 ("drm/qxl: simplify qxl_fence_wait")
- add missing code dependency from
  commit d72277b6c37d ("dma-buf: nuke DMA_FENCE_TRACE macros v2")

---

Hi,

To clarify, the reason for my original patch, as explained in more detail
in my previous email, was that it fixed the issue while keeping the code
simpler (which was the original reason for the commit being reverted here).
But I perfectly understand opting for previously battle tested code. Makes
sense.

As requested I've reverted commit 5a838e5d5825 ("drm/qxl: simplify qxl_fence_wait")
and then executed both Timo's and my test cases, and 1h video playback.
I was unable to reproduce the bug with any of those cases. So the revert
seems to fix the bug.
Please note, and as stated in the commit message, due to a dependency to
DMA_FENCE_WARN this patch also restores the relevant code deleted
by commit d72277b6c37d ("dma-buf: nuke DMA_FENCE_TRACE macros v2").

A couple of things I've observed from dmesg:
- (1) it always triggers a single warning at boot, this is issued by
  `WARN_ON(list_empty(&release->bos));` @ qxl_release_free @ qxl_release.c
  Maybe better for this to be addressed separately from this patch?
- (2) there are quite a few `failed to wait on release xx after spincount
  301` messages as printed by the patch v2 code when the test case shell
  scripts are being executed.
- (3) there can be a single error message `[drm:qxl_release_from_id_locked
  [qxl]] *ERROR* failed to find id in release_idr`
- (4) occasional error messages about `[drm:drm_atomic_helper_commit_planes
  [drm_kms_helper]] *ERROR* head 9 wrong:`.

Issue (1) relates to this patch v2 and also happened with kernel from
base-commit 1870cdc0e8de (March 1st).
Issue (2) also relates to this patch v2 but only happens with kernel from
base-commit a6bd6c933339 (March 30th).
Both (3) and (4) are unrelated to this patch as they can occur
independently of it and I'm guessing these may be related to the recent
changes discussed in
https://lore.kernel.org/dri-devel/38d38331-3848-4995-b78e-a87ecae722d5@linux.intel.com/T/#u


For reference here is the output of (1):
```
[   20.779514] ------------[ cut here ]------------
[   20.779525] workqueue: WQ_MEM_RECLAIM ttm:ttm_bo_delayed_delete [ttm] is flushing !WQ_MEM_RECLAIM events:qxl_gc_work [qxl]
[   20.779666] WARNING: CPU: 1 PID: 601 at kernel/workqueue.c:3692 check_flush_dependency+0xfa/0x110
[   20.779683] Modules linked in: nfsv3 nfs_acl nfs lockd grace intel_rapl_msr intel_rapl_common intel_pmc_core intel_vsec pmt_telemetry pmt_class kvm_intel rfkill kvm snd_hda_codec_generic crct10dif_pclmul crct10dif_common crc32_pclmul ghash_clmulni_intel snd_hda_intel snd_intel_dspcfg sha512_ssse3 sha512_generic snd_hda_codec sha256_ssse3 snd_hwdep sha1_ssse3 snd_hda_core sunrpc binfmt_misc snd_pcm aesni_intel qxl drm_ttm_helper ttm crypto_simd snd_timer cryptd rapl snd virtio_balloon virtio_console drm_kms_helper pcspkr soundcore button evdev joydev serio_raw drm loop fuse efi_pstore dm_mod configfs qemu_fw_cfg virtio_rng autofs4 ext4 crc32c_generic crc16 mbcache jbd2 virtio_net ata_generic net_failover virtio_blk failover uhci_hcd ata_piix ehci_hcd libata scsi_mod usbcore crc32c_intel i2c_piix4 virtio_pci virtio psmouse virtio_pci_legacy_dev virtio_pci_modern_dev virtio_ring floppy scsi_common usb_common
[   20.779825] CPU: 1 PID: 601 Comm: kworker/u13:1 Not tainted 6.9.0-rc1-next-20240328-amd64-00001-g756220c4615c #81
[   20.779833] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
[   20.779837] Workqueue: ttm ttm_bo_delayed_delete [ttm]
[   20.779862] RIP: 0010:check_flush_dependency+0xfa/0x110
[   20.779869] Code: ff ff 49 8b 55 18 48 8d 8b c0 00 00 00 49 89 e8 48 81 c6 c0 00 00 00 48 c7 c7 c0 16 44 8d c6 05 e7 75 b3 01 01 e8 86 97 fd ff <0f> 0b e9 21 ff ff ff 80 3d d5 75 b3 01 00 75 96 e9 4d ff ff ff 90
[   20.779875] RSP: 0000:ffffb59600dd7cc8 EFLAGS: 00010082
[   20.779880] RAX: 0000000000000000 RBX: ffff9af88104ee00 RCX: 0000000000000027
[   20.779902] RDX: ffff9af8fdd21708 RSI: 0000000000000001 RDI: ffff9af8fdd21700
[   20.779906] RBP: ffffffffc0882570 R08: 0000000000000000 R09: 0000000000000003
[   20.779910] R10: ffffb59600dd7b58 R11: ffffffff8dcc83e8 R12: ffff9af894498000
[   20.779914] R13: ffff9af89558d780 R14: ffffb59600dd7cf8 R15: 0000000000000001
[   20.779918] FS:  0000000000000000(0000) GS:ffff9af8fdd00000(0000) knlGS:0000000000000000
[   20.779924] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   20.779928] CR2: 00005574b0bd4148 CR3: 000000001fb40002 CR4: 0000000000370ef0
[   20.779994] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   20.779999] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   20.780003] Call Trace:
[   20.780135]  <TASK>
[   20.780144]  ? __warn+0x7c/0x120
[   20.780153]  ? check_flush_dependency+0xfa/0x110
[   20.780161]  ? report_bug+0x160/0x190
[   20.780169]  ? prb_read_valid+0x17/0x20
[   20.780179]  ? handle_bug+0x41/0x70
[   20.780186]  ? exc_invalid_op+0x13/0x60
[   20.780193]  ? asm_exc_invalid_op+0x16/0x20
[   20.780201]  ? __pfx_qxl_gc_work+0x10/0x10 [qxl]
[   20.780221]  ? check_flush_dependency+0xfa/0x110
[   20.780228]  ? check_flush_dependency+0xfa/0x110
[   20.780234]  __flush_work+0xce/0x2c0
[   20.780244]  qxl_queue_garbage_collect+0x7f/0x90 [qxl]
[   20.780268]  qxl_fence_wait+0xa0/0x190 [qxl]
[   20.780287]  dma_fence_wait_timeout+0x5e/0x130
[   20.780313]  dma_resv_wait_timeout+0x7b/0xe0
[   20.780327]  ttm_bo_delayed_delete+0x26/0x80 [ttm]
[   20.780359]  process_one_work+0x184/0x3a0
[   20.780370]  worker_thread+0x273/0x390
[   20.780379]  ? __pfx_worker_thread+0x10/0x10
[   20.780388]  kthread+0xcb/0x100
[   20.780396]  ? __pfx_kthread+0x10/0x10
[   20.780404]  ret_from_fork+0x2d/0x50
[   20.780416]  ? __pfx_kthread+0x10/0x10
[   20.780421]  ret_from_fork_asm+0x1a/0x30
[   20.780435]  </TASK>
[   20.780437] ---[ end trace 0000000000000000 ]---
```


TLDR: this patch fixes the instability issues. But there may be warnings
in dmesg. Errors in dmesg were observed too but they are unrelated to this
patch.


Thank you for your time.

---

Alex Constantino (1):
  Revert "drm/qxl: simplify qxl_fence_wait"

 drivers/gpu/drm/qxl/qxl_release.c | 50 +++++++++++++++++++++++++++----
 include/linux/dma-fence.h         |  7 +++++
 2 files changed, 52 insertions(+), 5 deletions(-)


base-commit: a6bd6c9333397f5a0e2667d4d82fef8c970108f2
-- 
2.39.2