[Intel-gfx] [PATCH] drm/i915: Keep drm_i915_file_private around under RCU

[Matthew Auld]

On Fri, 23 Aug 2019 at 19:15, Chris Wilson <chris at chris-wilson.co.uk> wrote:
>
> Ensure that the drm_i915_file_private continues to exist as we attempt
> to remove a request from its list, which may race with the destruction
> of the file.
>
> <6> [38.380714] [IGT] gem_ctx_create: starting subtest basic-files
> <0> [42.201329] BUG: spinlock bad magic on CPU#0, kworker/u16:0/7
> <4> [42.201356] general protection fault: 0000 [#1] PREEMPT SMP PTI
> <4> [42.201371] CPU: 0 PID: 7 Comm: kworker/u16:0 Tainted: G     U            5.3.0-rc5-CI-Patchwork_14169+ #1
> <4> [42.201391] Hardware name: Dell Inc.                 OptiPlex 745                 /0GW726, BIOS 2.3.1  05/21/2007
> <4> [42.201594] Workqueue: i915 retire_work_handler [i915]
> <4> [42.201614] RIP: 0010:spin_dump+0x5a/0x90
> <4> [42.201625] Code: 00 48 8d 88 c0 06 00 00 48 c7 c7 00 71 09 82 e8 35 ef 00 00 48 85 db 44 8b 4d 08 41 b8 ff ff ff ff 48 c7 c1 0b cd 0f 82 74 0e <44> 8b 83 e0 04 00 00 48 8d 8b c0 06 00 00 8b 55 04 48 89 ee 48 c7
> <4> [42.201660] RSP: 0018:ffffc9000004bd80 EFLAGS: 00010202
> <4> [42.201673] RAX: 0000000000000031 RBX: 6b6b6b6b6b6b6b6b RCX: ffffffff820fcd0b
> <4> [42.201688] RDX: 0000000000000000 RSI: ffff88803de266f8 RDI: 00000000ffffffff
> <4> [42.201703] RBP: ffff888038381ff8 R08: 00000000ffffffff R09: 000000006b6b6b6b
> <4> [42.201718] R10: 0000000041cb0b89 R11: 646162206b636f6c R12: ffff88802a618500
> <4> [42.201733] R13: ffff88802b32c288 R14: ffff888038381ff8 R15: ffff88802b32c250
> <4> [42.201748] FS:  0000000000000000(0000) GS:ffff88803de00000(0000) knlGS:0000000000000000
> <4> [42.201765] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> <4> [42.201778] CR2: 00007f2cefc6d180 CR3: 00000000381ee000 CR4: 00000000000006f0
> <4> [42.201793] Call Trace:
> <4> [42.201805]  do_raw_spin_lock+0x66/0xb0
> <4> [42.201898]  i915_request_retire+0x548/0x7c0 [i915]
> <4> [42.201989]  retire_requests+0x4d/0x60 [i915]
> <4> [42.202078]  i915_retire_requests+0x144/0x2e0 [i915]
> <4> [42.202169]  retire_work_handler+0x10/0x40 [i915]
>
> Recently, in commit 44c22f3f1a0a ("drm/i915: Serialize insertion into the
> file->mm.request_list"), we fixed a race on insertion. Now, it appears
> we also have a race with destruction!
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Matthew Auld <matthew.auld at intel.com>
Reviewed-by: Matthew Auld <matthew.auld at intel.com>