Re: WARNING in __put_task_struct (2)

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    774ea0551a29 Add linux-next specific files for 20181012
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17f71735400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=273e86a7f336b114
dashboard link: https://syzkaller.appspot.com/bug?extid=1ed9dfaa984c88cf0ef8
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1735d391400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1296a3a1400000

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

audit: type=1800 audit(1539536806.030:30): pid=5454 uid=0 auid=4294967295  
ses=4294967295 subj==unconfined op=collect_data cause=failed(directio)  
comm="startpar" name="rmnologin" dev="sda1" ino=2423 res=0
IPVS: ftp: loaded support on port[0] = 21
WARNING: CPU: 1 PID: 5614 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: 5614 Comm: syz-executor338 Not tainted  
4.19.0-rc7-next-20181012+ #93
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 c3 a3 7b 00 e9 a1 fe ff ff e8 69 55 37 00 0f 0b e9 7c fd  
ff ff e8 5d 55 37 00 0f 0b e9 87 fd ff ff e8 51 55 37 00 <0f> 0b e9 d0 fc  
ff ff e8 45 55 37 00 49 8d 87 90 05 00 00 31 f6 48
RSP: 0018:ffff8801d7fcee48 EFLAGS: 00010293
RAX: ffff8801d7ffe5c0 RBX: ffff8801d82be540 RCX: ffffffff814711cd
RDX: 0000000000000000 RSI: ffffffff814714ff RDI: 0000000000000005
RBP: ffff8801d7fcef28 R08: ffff8801d7ffe5c0 R09: ffffed003b057cac
R10: ffffed003b057cac R11: ffff8801d82be563 R12: 1ffff1003aff9dcc
R13: 0000000000000000 R14: ffff8801d7fcef00 R15: ffff8801d7f7a9c0
 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
 exit_task_work include/linux/task_work.h:22 [inline]
 do_exit+0x1ad2/0x2610 kernel/exit.c:867
 do_group_exit+0x177/0x440 kernel/exit.c:970
 get_signal+0x8a8/0x1970 kernel/signal.c:2517
 do_signal+0x9c/0x21c0 arch/x86/kernel/signal.c:816
 exit_to_usermode_loop+0x2e5/0x380 arch/x86/entry/common.c:162
 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: 0033:0x4460a9
Code: Bad RIP value.
RSP: 002b:00007f0e9c1a9da8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00000000006dbc48 RCX: 00000000004460a9
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00000000006dbc48
RBP: 00000000006dbc40 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc4c
R13: 666e692f7665642f R14: 0100000000000000 R15: 0000000000000003
Kernel Offset: disabled
Rebooting in 86400 seconds..