WARNING in __put_task_struct

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: d573e8a7 Linux 4.19.75
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1010f2f9600000
kernel config: https://syzkaller.appspot.com/x/.config?x=50b385e67c7b7cdf
dashboard link: https://syzkaller.appspot.com/bug?extid=0b1cffc6e907317ff3db
compiler: gcc (GCC) 9.0.0 20181231 (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+0b1cff...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 1 PID: 13047 at kernel/fork.c:677
__put_task_struct.cold+0x29/0x48 kernel/fork.c:677
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 13047 Comm: syz-executor.4 Not tainted 4.19.75 #0
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+0x172/0x1f0 lib/dump_stack.c:113
panic+0x263/0x507 kernel/panic.c:185
__warn.cold+0x20/0x4a kernel/panic.c:540
report_bug+0x263/0x2b0 lib/bug.c:186
fixup_bug arch/x86/kernel/traps.c:178 [inline]
fixup_bug arch/x86/kernel/traps.c:173 [inline]
do_error_trap+0x204/0x360 arch/x86/kernel/traps.c:296
do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:316
invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:1037
RIP: 0010:__put_task_struct.cold+0x29/0x48 kernel/fork.c:677
Code: ff e8 20 7d 2c 00 48 c7 c7 20 45 49 87 e8 f8 e3 16 00 0f 0b e9 34 4b
ff ff e8 08 7d 2c 00 48 c7 c7 20 45 49 87 e8 e0 e3 16 00 <0f> 0b e9 c5 4a
ff ff e8 f0 7c 2c 00 48 c7 c7 20 45 49 87 e8 c8 e3
RSP: 0018:ffff88804dc87cd8 EFLAGS: 00010286
RAX: 0000000000000024 RBX: 0000000000000000 RCX: 0000000000000000
kobject: 'loop5' (00000000578a77fd): kobject_uevent_env
RDX: 0000000000000000 RSI: ffffffff8155dbd6 RDI: ffffed1009b90f8d
RBP: ffff88804dc87d00 R08: 0000000000000024 R09: ffffed1015d25079
R10: ffffed1015d25078 R11: ffff8880ae9283c7 R12: ffff888051c2e180
R13: ffff88805d2d7770 R14: 0000000000000000 R15: 0000000000000000
put_task_struct include/linux/sched/task.h:96 [inline]
rdma_restrack_del+0x1da/0x240 drivers/infiniband/core/restrack.c:229
rdma_destroy_id+0xac/0xab0 drivers/infiniband/core/cma.c:1726
kobject: 'loop5' (00000000578a77fd): fill_kobj_path: path
= '/devices/virtual/block/loop5'
ucma_close+0x115/0x320 drivers/infiniband/core/ucma.c:1770
__fput+0x2dd/0x8b0 fs/file_table.c:278
____fput+0x16/0x20 fs/file_table.c:309
task_work_run+0x145/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:193 [inline]
exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:167
prepare_exit_to_usermode arch/x86/entry/common.c:198 [inline]
syscall_return_slowpath arch/x86/entry/common.c:271 [inline]
do_syscall_64+0x53d/0x620 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4136f1
Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 1b 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:00007ffd5ff69000 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 00000000004136f1
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 0000000000000000 R08: ffffffffffffffff R09: ffffffffffffffff
R10: 00007ffd5ff690e0 R11: 0000000000000293 R12: 000000000075bfc8
R13: 000000000004aae3 R14: 00000000007605d0 R15: 000000000075bfd4
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.