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Date:   Fri, 16 Jun 2023 11:52:18 -0700
Message-ID: <0000000000002b6ab405fe43af4a@google.com>
Subject: [syzbot] [kernel?] possible deadlock in exit_itimers
From:   syzbot <syzbot+5fd924f4cd9dc1c7828c@syzkaller.appspotmail.com>
To:     linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        tglx@linutronix.de
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Hello,

syzbot found the following issue on:

HEAD commit:    f7efed9f38f8 Add linux-next specific files for 20230616
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=124a65f7280000
kernel config:  https://syzkaller.appspot.com/x/.config?x=60b1a32485a77c16
dashboard link: https://syzkaller.appspot.com/bug?extid=5fd924f4cd9dc1c7828c
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1401d8ef280000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=176b45cf280000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/95bcbee03439/disk-f7efed9f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6fd295caa4de/vmlinux-f7efed9f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/69c038a34b5f/bzImage-f7efed9f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5fd924f4cd9dc1c7828c@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
6.4.0-rc6-next-20230616-syzkaller #0 Not tainted
--------------------------------------------
syz-executor196/6178 is trying to acquire lock:
ffff88801eccb640 (&new_timer->it_lock){-.-.}-{2:2}, at: itimer_delete kernel/time/posix-timers.c:1049 [inline]
ffff88801eccb640 (&new_timer->it_lock){-.-.}-{2:2}, at: exit_itimers+0x2ac/0x540 kernel/time/posix-timers.c:1109

but task is already holding lock:
ffff88801eccb640 (&new_timer->it_lock){-.-.}-{2:2}, at: __lock_timer+0x1cc/0x4d0 kernel/time/posix-timers.c:595

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&new_timer->it_lock);
  lock(&new_timer->it_lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

1 lock held by syz-executor196/6178:
 #0: ffff88801eccb640 (&new_timer->it_lock){-.-.}-{2:2}, at: __lock_timer+0x1cc/0x4d0 kernel/time/posix-timers.c:595

stack backtrace:
CPU: 1 PID: 6178 Comm: syz-executor196 Not tainted 6.4.0-rc6-next-20230616-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106
 check_deadlock kernel/locking/lockdep.c:3070 [inline]
 validate_chain kernel/locking/lockdep.c:3863 [inline]
 __lock_acquire+0x2a33/0x5e20 kernel/locking/lockdep.c:5144
 lock_acquire.part.0+0x11c/0x370 kernel/locking/lockdep.c:5761
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x3d/0x60 kernel/locking/spinlock.c:162
 itimer_delete kernel/time/posix-timers.c:1049 [inline]
 exit_itimers+0x2ac/0x540 kernel/time/posix-timers.c:1109
 do_exit+0x630/0x2a30 kernel/exit.c:848
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1024
 __do_sys_exit_group kernel/exit.c:1035 [inline]
 __se_sys_exit_group kernel/exit.c:1033 [inline]
 __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1033
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f5dc8cc4dd9
Code: 00 49 c7 c0 b8 ff ff ff be e7 00 00 00 ba 3c 00 00 00 eb 12 0f 1f 44 00 00 89 d0 0f 05 48 3d 00 f0 ff ff 77 1c f4 89 f0 0f 05 <48> 3d 00 f0 ff ff 76 e7 f7 d8 64 41 89 00 eb df 0f 1f 80 00 00 00
RSP: 002b:00007ffe0c959208 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 00007f5dc8d4f210 RCX: 00007f5dc8cc4dd9
RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffffffffffb8 R09: 00007f5dc8d151cf
R10: 00007ffe0c959290 R11: 0000000000000246 R12: 00007f5dc8d4f210
R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000001
 </TASK>


---
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