Date: Wed, 3 Jan 2024 16:12:41 +0100
From: Christian König <christian.koenig@....com>
To: Qi Zheng <zhengqi.arch@...edance.com>,
 syzbot <syzbot+59dcc2e7283a6f5f5ba1@...kaller.appspotmail.com>
Cc: airlied@...il.com, akinobu.mita@...il.com, akpm@...ux-foundation.org,
 daniel@...ll.ch, dri-devel@...ts.freedesktop.org, jgg@...dia.com,
 linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
 linux-media@...r.kernel.org, maarten.lankhorst@...ux.intel.com,
 mripard@...nel.org, sumit.semwal@...aro.org,
 syzkaller-bugs@...glegroups.com, tzimmermann@...e.de
Subject: Re: [syzbot] [dri?] WARNING in drm_prime_destroy_file_private (2)

Am 28.12.23 um 03:57 schrieb Qi Zheng:
>
>
> On 2023/12/28 04:51, syzbot wrote:
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit:    5254c0cbc92d Merge tag 'block-6.7-2023-12-22' of 
>> git://git..
>> git tree:       upstream
>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=10cc6995e80000
>> kernel config: 
>> https://syzkaller.appspot.com/x/.config?x=314e9ad033a7d3a7
>> dashboard link: 
>> https://syzkaller.appspot.com/bug?extid=59dcc2e7283a6f5f5ba1
>> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils 
>> for Debian) 2.40
>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13e35809e80000
>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=155d5fd6e80000
>>
>> Downloadable assets:
>> disk image: 
>> https://storage.googleapis.com/syzbot-assets/ebe09a5995ee/disk-5254c0cb.raw.xz
>> vmlinux: 
>> https://storage.googleapis.com/syzbot-assets/02178d7f5f98/vmlinux-5254c0cb.xz
>> kernel image: 
>> https://storage.googleapis.com/syzbot-assets/12307f47d87c/bzImage-5254c0cb.xz
>>
>> The issue was bisected to:
>>
>> commit ea4452de2ae987342fadbdd2c044034e6480daad
>> Author: Qi Zheng <zhengqi.arch@...edance.com>
>> Date:   Fri Nov 18 10:00:11 2022 +0000
>>
>>      mm: fix unexpected changes to {failslab|fail_page_alloc}.attr
>>
>> bisection log: 
>> https://syzkaller.appspot.com/x/bisect.txt?x=13027f76e80000
>> final oops: https://syzkaller.appspot.com/x/report.txt?x=10827f76e80000
>> console output: https://syzkaller.appspot.com/x/log.txt?x=17027f76e80000
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the 
>> commit:
>> Reported-by: syzbot+59dcc2e7283a6f5f5ba1@...kaller.appspotmail.com
>> Fixes: ea4452de2ae9 ("mm: fix unexpected changes to 
>> {failslab|fail_page_alloc}.attr")
>>
>> R10: 0000000000000000 R11: 0000000000000246 R12: 00007efe98069194
>> R13: 00007efe97fd2210 R14: 0000000000000002 R15: 6972642f7665642f
>>   </TASK>
>> ------------[ cut here ]------------
>> WARNING: CPU: 0 PID: 5107 at drivers/gpu/drm/drm_prime.c:227 
>> drm_prime_destroy_file_private+0x43/0x60 drivers/gpu/drm/drm_prime.c:227
>
> The warning is caused by !RB_EMPTY_ROOT(&prime_fpriv->dmabufs):
>
> drm_prime_destroy_file_private
> --> WARN_ON(!RB_EMPTY_ROOT(&prime_fpriv->dmabufs));
>
> It seems irrelevant to the logic of fault injection. So I don't see
> why the commit ea4452de2ae9 can cause this warning. :(

Making an educated guess I strongly think syzbot incorrectly bisected this.

What basically happens is that a DRM test case crashes because a file 
private data structure is destroyed before all DMA-bufs referring to it 
are destroyed.

Looks like a random race condition in a test case to me. Question is 
really what test is syzbot running and who is maintaining this test case?

Regards,
Christian.

>
>> Modules linked in:
>> CPU: 0 PID: 5107 Comm: syz-executor227 Not tainted 
>> 6.7.0-rc6-syzkaller-00248-g5254c0cbc92d #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, 
>> BIOS Google 11/17/2023
>> RIP: 0010:drm_prime_destroy_file_private+0x43/0x60 
>> drivers/gpu/drm/drm_prime.c:227
>> Code: 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 75 21 48 8b 83 
>> 90 00 00 00 48 85 c0 75 06 5b e9 13 f1 93 fc e8 0e f1 93 fc 90 <0f> 
>> 0b 90 5b e9 04 f1 93 fc e8 3f 9b ea fc eb d8 66 66 2e 0f 1f 84
>> RSP: 0018:ffffc90003bdf9e0 EFLAGS: 00010293
>> RAX: 0000000000000000 RBX: ffff888019f28378 RCX: ffffc90003bdf9b0
>> RDX: ffff888018ff9dc0 RSI: ffffffff84f380c2 RDI: ffff888019f28408
>> RBP: ffff888019f28000 R08: 0000000000000001 R09: 0000000000000001
>> R10: ffffffff8f193a57 R11: 0000000000000000 R12: ffff88814829a000
>> R13: ffff888019f282a8 R14: ffff88814829a068 R15: ffff88814829a0a0
>> FS:  0000000000000000(0000) GS:ffff8880b9800000(0000) 
>> knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007efe98050410 CR3: 000000006d1ff000 CR4: 0000000000350ef0
>> Call Trace:
>>   <TASK>
>>   drm_file_free.part.0+0x738/0xb90 drivers/gpu/drm/drm_file.c:290
>>   drm_file_free drivers/gpu/drm/drm_file.c:247 [inline]
>>   drm_close_helper.isra.0+0x180/0x1f0 drivers/gpu/drm/drm_file.c:307
>>   drm_release+0x22a/0x4f0 drivers/gpu/drm/drm_file.c:494
>>   __fput+0x270/0xb70 fs/file_table.c:394
>>   task_work_run+0x14d/0x240 kernel/task_work.c:180
>>   exit_task_work include/linux/task_work.h:38 [inline]
>>   do_exit+0xa8a/0x2ad0 kernel/exit.c:869
>>   do_group_exit+0xd4/0x2a0 kernel/exit.c:1018
>>   get_signal+0x23b5/0x2790 kernel/signal.c:2904
>>   arch_do_signal_or_restart+0x90/0x7f0 arch/x86/kernel/signal.c:309
>>   exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
>>   exit_to_user_mode_prepare+0x121/0x240 kernel/entry/common.c:204
>>   __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
>>   syscall_exit_to_user_mode+0x1e/0x60 kernel/entry/common.c:296
>>   do_syscall_64+0x4d/0x110 arch/x86/entry/common.c:89
>>   entry_SYSCALL_64_after_hwframe+0x63/0x6b
>> RIP: 0033:0x7efe98014769
>> Code: Unable to access opcode bytes at 0x7efe9801473f.
>> RSP: 002b:00007efe97fd2208 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
>> RAX: fffffffffffffe00 RBX: 00007efe9809c408 RCX: 00007efe98014769
>> RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007efe9809c408
>> RBP: 00007efe9809c400 R08: 0000000000003131 R09: 0000000000003131
>> R10: 0000000000000000 R11: 0000000000000246 R12: 00007efe98069194
>> R13: 00007efe97fd2210 R14: 0000000000000002 R15: 6972642f7665642f
>>   </TASK>
>>
>>
>> ---
>> This report is generated by a bot. It may contain errors.
>> See https://goo.gl/tpsmEJ for more information about syzbot.
>> syzbot engineers can be reached at syzkaller@...glegroups.com.
>>
>> syzbot will keep track of this issue. See:
>> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>> For information about bisection process see: 
>> https://goo.gl/tpsmEJ#bisection
>>
>> If the report is already addressed, let syzbot know by replying with:
>> #syz fix: exact-commit-title
>>
>> If you want syzbot to run the reproducer, reply with:
>> #syz test: git://repo/address.git branch-or-commit-hash
>> If you attach or paste a git patch, syzbot will apply it before testing.
>>
>> If you want to overwrite report's subsystems, reply with:
>> #syz set subsystems: new-subsystem
>> (See the list of subsystem names on the web dashboard)
>>
>> If the report is a duplicate of another one, reply with:
>> #syz dup: exact-subject-of-another-report
>>
>> If you want to undo deduplication, reply with:
>> #syz undup

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