WARNING in __put_task_struct (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    ae16eea39a86 Add linux-next specific files for 20181008
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12e7c6a1400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=42525ce985d1a955
dashboard link: https://syzkaller.appspot.com/bug?extid=1ed9dfaa984c88cf0ef8
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+1ed9dfaa984c88cf0ef8@xxxxxxxxxxxxxxxxxxxxxxxxx

WARNING: CPU: 1 PID: 16271 at kernel/fork.c:718  
__put_task_struct+0x3ef/0x620 kernel/fork.c:718
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 16271 Comm: syz-executor5 Not tainted 4.19.0-rc7-next-20181008+  
#89
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x244/0x3ab lib/dump_stack.c:113
 panic+0x238/0x4e7 kernel/panic.c:184
 __warn.cold.8+0x163/0x1ba kernel/panic.c:536
 report_bug+0x254/0x2d0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:178 [inline]
 do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
 do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:969
RIP: 0010:__put_task_struct+0x3ef/0x620 kernel/fork.c:718
Code: 4c 89 ee e8 d3 9d 7b 00 e9 a1 fe ff ff e8 89 53 37 00 0f 0b e9 7c fd  
ff ff e8 7d 53 37 00 0f 0b e9 87 fd ff ff e8 71 53 37 00 <0f> 0b e9 d0 fc  
ff ff e8 65 53 37 00 49 8d 87 90 05 00 00 31 f6 48
RSP: 0018:ffff88018dbcf808 EFLAGS: 00010293
RAX: ffff880187474180 RBX: ffff88018cc7a1c0 RCX: ffffffff8147298d
RDX: 0000000000000000 RSI: ffffffff81472cbf RDI: 0000000000000005
RBP: ffff88018dbcf8e8 R08: ffff880187474180 R09: ffffed003198f43c
R10: ffffed003198f43c R11: ffff88018cc7a1e3 R12: 1ffff10031b79f04
R13: 0000000000000000 R14: ffff88018dbcf8c0 R15: ffff88018daceb40
 put_task_struct include/linux/sched/task.h:96 [inline]
 rdma_restrack_del+0x2e0/0x3b0 drivers/infiniband/core/restrack.c:243
 rdma_destroy_id+0x126/0xcc0 drivers/infiniband/core/cma.c:1820
 ucma_close+0x114/0x310 drivers/infiniband/core/ucma.c:1767
 __fput+0x3bc/0xa70 fs/file_table.c:279
 ____fput+0x15/0x20 fs/file_table.c:312
 task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
 do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x411051
Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 34 19 00 00 c3 48  
83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48  
89 c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007ffd6e8617b0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000005 RCX: 0000000000411051
RDX: 0000000000000000 RSI: 0000000000731850 RDI: 0000000000000004
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 00007ffd6e8616e0 R11: 0000000000000293 R12: 0000000000000000
R13: 0000000000000001 R14: 0000000000000156 R15: 0000000000000005
Kernel Offset: disabled
Rebooting in 86400 seconds..


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