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.... vmlinux: https://storage.googleapis.com/syzbot-assets/02178d7f5f98/vmlinux-5254c0cb.x... kernel image: https://storage.googleapis.com/syzbot-assets/12307f47d87c/bzImage-5254c0cb.x...

The issue was bisected to:

commit ea4452de2ae987342fadbdd2c044034e6480daad Author: Qi Zheng zhengqi.arch@bytedance.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@syzkaller.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>

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