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Sat, 07 Nov 2026 21:52:28 -0800 (PST) Date: Sat, 07 Nov 2026 21:52:28 -0800 In-Reply-To: <6aee17c4.8be4ead1.3b45e1.0199.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6af00e1c.5a668245.1aceb6.0005.GAE@google.com> Subject: Re: [syzbot] [nfs?] [net?] WARNING in svc_destroy From: syzbot To: anna@kernel.org, cel@kernel.org, dai.ngo@oracle.com, davem@davemloft.net, edumazet@kernel.org, horms@kernel.org, jlayton@kernel.org, kuba@kernel.org, linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, neil@brown.name, netdev@vger.kernel.org, okorniev@redhat.com, pabeni@redhat.com, syzkaller-bugs@googlegroups.com, tom@talpey.com, trondmy@kernel.org Content-Type: text/plain; charset="UTF-8" syzbot has found a reproducer for the following issue on: HEAD commit: d164c7d754f0 Merge tag 'devicetree-fixes-for-7.4-1' of git.. git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git console output: https://syzkaller.appspot.com/x/log.txt?x=13ac11a1580000 kernel config: https://syzkaller.appspot.com/x/.config?x=1cf189394a856f11 dashboard link: https://syzkaller.appspot.com/bug?extid=8cbdf9aa6c281a4e6bbe compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1494d369580000 AI-generated root cause summary: In fs/nfs/callback.c, nfs4_callback_up_net() first initializes an IPv4 TCP listener transport via svc_xprt_create(..., PF_INET, ...), which links the transport onto serv->sv_permsocks. When a subsequent call to svc_xprt_create(..., PF_INET6, ...) fails with an error other than -EAFNOSUPPORT, nfs4_callback_up_net() returns the error immediately without tearing down the existing IPv4 transport. As a result, nfs_callback_up() unwinds on error and calls xprt_svc_destroy_nullify_bc() -> svc_destroy(), which triggers the WARN_ONCE(!list_empty(&serv->sv_permsocks)) warning because the IPv4 transport is still attached to the service, and subsequently frees the service while leaving the active listener with a dangling pointer. full analysis: https://syzkaller.appspot.com/x/ai_root_cause?x=8cbdf9aa6c281a4e6bbe IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+8cbdf9aa6c281a4e6bbe@syzkaller.appspotmail.com NFS: callback service start failed ------------[ cut here ]------------ SVC: permsocks remain for NFSv4 callback WARNING: net/sunrpc/svc.c:532 at svc_destroy+0x299/0x330 net/sunrpc/svc.c:532, CPU#1: syz-executor154/6024 Modules linked in: CPU: 1 UID: 0 PID: 6024 Comm: syz-executor154 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/06/2026 RIP: 0010:svc_destroy+0x29d/0x330 net/sunrpc/svc.c:532 Code: 48 b8 00 00 00 00 00 fc ff df 49 8b 5d 00 48 8d 7b 18 48 89 fa 48 c1 ea 03 80 3c 02 00 75 67 48 8d 3d e7 6d 77 07 48 8b 73 18 <67> 48 0f b9 3a e9 d0 fd ff ff 48 8b 7c 24 08 e8 7f 4d 85 f7 e9 a5 RSP: 0018:ffffc9000393f860 EFLAGS: 00010246 RAX: dffffc0000000000 RBX: ffffffff9040bf80 RCX: 0000000000000000 RDX: 1ffffffff20817f3 RSI: ffffffff8c37ebc0 RDI: ffffffff927b0660 RBP: 0000000000000000 R08: 00000000ffffffff R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000000 R12: ffff888020bcc000 R13: ffff8880274a0000 R14: ffff88802c3c4000 R15: ffffffff9cd624c0 FS: 000055556ff69400(0000) GS:ffff888122575000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000055fdb0009fd0 CR3: 00000000377ff000 CR4: 00000000003526f0 Call Trace: nfs_callback_up+0x511/0xad0 fs/nfs/callback.c:236 nfs4_init_callback fs/nfs/nfs4client.c:327 [inline] nfs4_init_client_minor_version fs/nfs/nfs4client.c:379 [inline] nfs4_init_client+0x236/0x420 fs/nfs/nfs4client.c:429 nfs_get_client+0xf38/0x1230 fs/nfs/client.c:467 nfs4_set_client+0x3f6/0x640 fs/nfs/nfs4client.c:763 nfs4_init_server.isra.0+0x5be/0xf80 fs/nfs/nfs4client.c:1014 nfs4_create_server+0x185/0x2b0 fs/nfs/nfs4client.c:1063 nfs4_try_get_tree+0x93/0x140 fs/nfs/nfs4super.c:228 nfs_get_tree+0xa61/0x1440 fs/nfs/fs_context.c:1621 vfs_get_tree+0x92/0x320 fs/super.c:1881 fc_mount fs/namespace.c:1282 [inline] do_new_mount_fc fs/namespace.c:3910 [inline] do_new_mount fs/namespace.c:3986 [inline] path_mount+0x7d0/0x2850 fs/namespace.c:4337 do_mount fs/namespace.c:4350 [inline] __do_sys_mount fs/namespace.c:4565 [inline] __se_sys_mount fs/namespace.c:4542 [inline] __x64_sys_mount+0x293/0x310 fs/namespace.c:4542 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fd324de7f1a Code: 48 c7 c2 d8 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 d8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffca5d506e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fd324de7f1a RDX: 00007fd324e4603f RSI: 00007fd324e45ffe RDI: 00007fd324e46044 RBP: 0000000000000004 R08: 00007ffca5d50760 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007fd324e45ffe R13: 0000000000001789 R14: 0000000000000801 R15: 00007ffca5d50760 ---------------- Code disassembly (best guess): 0: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax 7: fc ff df a: 49 8b 5d 00 mov 0x0(%r13),%rbx e: 48 8d 7b 18 lea 0x18(%rbx),%rdi 12: 48 89 fa mov %rdi,%rdx 15: 48 c1 ea 03 shr $0x3,%rdx 19: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) 1d: 75 67 jne 0x86 1f: 48 8d 3d e7 6d 77 07 lea 0x7776de7(%rip),%rdi # 0x7776e0d 26: 48 8b 73 18 mov 0x18(%rbx),%rsi * 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction 2f: e9 d0 fd ff ff jmp 0xfffffe04 34: 48 8b 7c 24 08 mov 0x8(%rsp),%rdi 39: e8 7f 4d 85 f7 call 0xf7854dbd 3e: e9 .byte 0xe9 3f: a5 movsl %ds:(%rsi),%es:(%rdi) --- 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.