Re: [PATCH] drm/nouveau: don't bump pin count on failed re-pin in nouveau_bo_pin_locked()

From: Peiyang He

Date: Thu Sep 17 2026 - 23:00:50 EST

On 2026/9/18 05:20, lyude@xxxxxxxxxx wrote:
> On Thu, 2026-09-10 at 16:06 +0800, Peiyang He wrote:
>> nouveau_bo_pin_locked() checks whether an already pinned BO is in a
>> memory domain compatible with a new pin request. When the domains are
>> incompatible, it sets -EBUSY but still calls ttm_bo_pin() before
>> returning.
>>
>> Callers treat a failed nouveau_bo_pin() as not having acquired a new
>> pin,
>> so the extra pin count is never decreased by a matching unpin.
>> This triggers the warning in ttm_bo_release():
>>
>> WARN_ON_ONCE(bo->pin_count);
>>
>> Found when fuzzing the nouveau driver with a modified Syzkaller:
>>
>> WARNING: drivers/gpu/drm/ttm/ttm_bo.c:256 at
>> ttm_bo_release+0x827/0x9e0 drivers/gpu/drm/ttm/ttm_bo.c:256, CPU#1:
>> syz.3.24/2212
>> Modules linked in:
>> CPU: 1 UID: 0 PID: 2212 Comm: syz.3.24 Not tainted 7.2.0 #24
>> PREEMPT(lazy)
>> nouveau 0000:01:00.0: gsp:msg fn:103 len:0x40/0x20 res:0x19
>> resp:0x19
>> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
>> 1.16.3-debian-1.16.3-2 04/01/2014
>> RIP: 0010:ttm_bo_release+0x827/0x9e0
>> drivers/gpu/drm/ttm/ttm_bo.c:256
>> Code: 02 00 0f 85 51 01 00 00 48 8b 7b 08 e8 d2 20 01 00 e9
>> 80 fd ff ff e8 d8 15 c0 fe 90 0f 0b 90 e9 e1 f8 ff ff e8 ca 15 c0 fe
>> 90 <0f> 0b 90 e9 a4 f8 ff ff e8 bc 15 c0 fe be 03 00 00 00 4c 89 e7
>> e8
>> msg: 00000000: 05 00 d0 c1 04 00 f0 f1 01 30 00 00 2d 90 00
>> 00 .........0..-...
>> RSP: 0018:ffffc9000f5cf710 EFLAGS: 00010293
>> RAX: 0000000000000000 RBX: ffff888018e5d2a8 RCX:
>> ffffffff82bb1b36
>> RDX: ffff888017b68000 RSI: 0000000000000004 RDI:
>> ffff888018e5d2a8
>> msg: 00000010: 19 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> 00 ................
>> RBP: ffff88801261c720 R08: 0000000000000001 R09:
>> ffffed10031cba55
>> R10: ffff888018e5d2ab R11: 00000000000000f3 R12:
>> ffff888018e5d290
>> R13: ffff888018e5d2d4 R14: ffff88801b219c18 R15:
>> dffffc0000000000
>> FS: 0000000000000000(0000) GS:ffff8880e0f6f000(0000)
>> knlGS:0000000000000000
>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 0000001b31223ffc CR3: 0000000028e00005 CR4:
>> 0000000000770ef0
>> PKRU: 80000000
>> Call Trace:
>> <TASK>
>> kref_put include/linux/kref.h:65 [inline]
>> ttm_bo_put drivers/gpu/drm/ttm/ttm_bo.c:325 [inline]
>> ttm_bo_fini+0x55/0x80 drivers/gpu/drm/ttm/ttm_bo.c:330
>> nouveau_gem_object_del+0xb2/0x1b0
>> drivers/gpu/drm/nouveau/nouveau_gem.c:90
>> drm_gem_object_free+0x5f/0x90 drivers/gpu/drm/drm_gem.c:1165
>> kref_put include/linux/kref.h:65 [inline]
>> __drm_gem_object_put include/drm/drm_gem.h:562 [inline]
>> drm_gem_object_put include/drm/drm_gem.h:575 [inline]
>> nouveau_abi16_chan_fini.constprop.0+0x44f/0x5a0
>> drivers/gpu/drm/nouveau/nouveau_abi16.c:195
>> nouveau 0000:01:00.0: syz.2.23[2209]: Unknown handle
>> 0x00000000
>> nouveau_abi16_fini+0x1d0/0x340
>> drivers/gpu/drm/nouveau/nouveau_abi16.c:225
>> nouveau_drm_postclose+0x18b/0x3e0
>> drivers/gpu/drm/nouveau/nouveau_drm.c:1284
>> nouveau 0000:01:00.0: syz.2.23[2209]: validate_init
>> drm_file_free.part.0+0x6d6/0xb60
>> drivers/gpu/drm/drm_file.c:267
>> drm_file_free drivers/gpu/drm/drm_file.c:237 [inline]
>> drm_close_helper.isra.0+0x11a/0x160
>> drivers/gpu/drm/drm_file.c:290
>> drm_release+0x1ab/0x330 drivers/gpu/drm/drm_file.c:438
>> __fput+0x39c/0xa60 fs/file_table.c:512
>> nouveau 0000:01:00.0: syz.2.23[2209]: validate: -2
>> task_work_run+0x15a/0x230 kernel/task_work.c:233
>> exit_task_work include/linux/task_work.h:40 [inline]
>> do_exit+0x82b/0x25a0 kernel/exit.c:1009
>> do_group_exit+0xc2/0x280 kernel/exit.c:1152
>> get_signal+0x1d6e/0x1f30 kernel/signal.c:3046
>> arch_do_signal_or_restart+0x7d/0x6e0
>> arch/x86/kernel/signal.c:337
>> __exit_to_user_mode_loop kernel/entry/common.c:66 [inline]
>> exit_to_user_mode_loop+0xdf/0x440 kernel/entry/common.c:101
>> __exit_to_user_mode_prepare include/linux/irq-entry-
>> common.h:207 [inline]
>> syscall_exit_to_user_mode_prepare include/linux/irq-entry-
>> common.h:230 [inline]
>> syscall_exit_to_user_mode include/linux/entry-common.h:318
>> [inline]
>> do_syscall_64+0x4f8/0x690 arch/x86/entry/syscall_64.c:100
>> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>> RIP: 0033:0x7f12bac8594d
>> Code: Unable to access opcode bytes at 0x7f12bac85923.
>> RSP: 002b:00007f12b96e70d8 EFLAGS: 00000246 ORIG_RAX:
>> 00000000000000ca
>> RAX: 0000000000000001 RBX: 00007f12baf15fa8 RCX:
>> 00007f12bac8594d
>> RDX: 00000000000f4240 RSI: 0000000000000081 RDI:
>> 00007f12baf15fac
>> RBP: 00007f12baf15fa0 R08: 00007f12baee8000 R09:
>> 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000246 R12:
>> 0000000000000000
>> R13: 00007f12baf16038 R14: 0000000000000006 R15:
>> 00007ffe2ed394b0
>> </TASK>
>> irq event stamp: 47867
>> hardirqs last enabled at (47883): [<ffffffff815cafc6>]
>> __up_console_sem+0x66/0x70 kernel/printk/printk.c:347
>> hardirqs last disabled at (47892): [<ffffffff815cafab>]
>> __up_console_sem+0x4b/0x70 kernel/printk/printk.c:345
>> softirqs last enabled at (47880): [<ffffffff81434277>]
>> __do_softirq kernel/softirq.c:656 [inline]
>> softirqs last enabled at (47880): [<ffffffff81434277>]
>> invoke_softirq kernel/softirq.c:496 [inline]
>> softirqs last enabled at (47880): [<ffffffff81434277>]
>> __irq_exit_rcu+0x137/0x1c0 kernel/softirq.c:735
>> softirqs last disabled at (47875): [<ffffffff81434277>]
>> __do_softirq kernel/softirq.c:656 [inline]
>> softirqs last disabled at (47875): [<ffffffff81434277>]
>> invoke_softirq kernel/softirq.c:496 [inline]
>> softirqs last disabled at (47875): [<ffffffff81434277>]
>> __irq_exit_rcu+0x137/0x1c0 kernel/softirq.c:735
>>
>> Fix by going to the out path as soon as the incompatible placement
>> is detected. This matches the correct bahaviour in other DRM drivers
>> such as amdgpu_bo_pin() in amdgpu.
>>
>> Cc: stable@xxxxxxxxxxxxxxx
>> Fixes: ad76b3f7c7a0 ("drm/nouveau: teach nouveau_bo_pin() how to
>> force a contig vram allocation")
>> Signed-off-by: Peiyang He <peiyang_he@xxxxxxxxxxxxxxxx>
>> Assisted-by: Codex:gpt-5.5
>
> This can and probably should just be:
>
> Assisted-by: LLM
>
> Instead of mentioning the LLM specifically used.
>
>> ---
>> drivers/gpu/drm/nouveau/nouveau_bo.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c
>> b/drivers/gpu/drm/nouveau/nouveau_bo.c
>> index 0e8de6d4b36f..bdd0390b590e 100644
>> --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
>> +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
>> @@ -578,6 +578,7 @@ int nouveau_bo_pin_locked(struct nouveau_bo
>> *nvbo, uint32_t domain, bool contig)
>> "0x%08x vs 0x%08x\n", bo,
>> bo->resource->mem_type, domain);
>> ret = -EBUSY;
>> + goto out;
>
> Would probably be better to just turn this into an else:
>
> if (error) {
> NV_ERROR(drm, "bo %p pinned elsewhere: "
> "0x%08x vs 0x%08x\n", bo,
> bo->resource->mem_type, domain);
> ret = -EBUSY;
> } else {
> ttm_bo_pin(&nvbo->bo);
> }
>
>
>> }
>> ttm_bo_pin(&nvbo->bo);
>> goto out;
>>
>> base-commit: df2908090cda368b01ff43709f51890076c56157
>
>

Thanks for your review! V2 sent.

Best,
Peiyang He