WARNING: suspicious RCU usage in ctrl_cmd_new_lookup

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    7ae77150 Merge tag 'powerpc-5.8-1' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14a3bcf9100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d195fe572fb15312
dashboard link: https://syzkaller.appspot.com/bug?extid=3025b9294f8cb0ede850
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11802cf9100000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=144acc03100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+3025b9294f8cb0ede850@xxxxxxxxxxxxxxxxxxxxxxxxx

=============================
WARNING: suspicious RCU usage
5.7.0-syzkaller #0 Not tainted
-----------------------------
include/linux/radix-tree.h:176 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
2 locks held by kworker/u4:0/7:
 #0: ffff88821b0bd138 ((wq_completion)qrtr_ns_handler){+.+.}-{0:0}, at: __write_once_size include/linux/compiler.h:279 [inline]
 #0: ffff88821b0bd138 ((wq_completion)qrtr_ns_handler){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff88821b0bd138 ((wq_completion)qrtr_ns_handler){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:855 [inline]
 #0: ffff88821b0bd138 ((wq_completion)qrtr_ns_handler){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:40 [inline]
 #0: ffff88821b0bd138 ((wq_completion)qrtr_ns_handler){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:615 [inline]
 #0: ffff88821b0bd138 ((wq_completion)qrtr_ns_handler){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:642 [inline]
 #0: ffff88821b0bd138 ((wq_completion)qrtr_ns_handler){+.+.}-{0:0}, at: process_one_work+0x844/0x16a0 kernel/workqueue.c:2239
 #1: ffffc90000cdfdc0 ((work_completion)(&qrtr_ns.work)){+.+.}-{0:0}, at: process_one_work+0x878/0x16a0 kernel/workqueue.c:2243

stack backtrace:
CPU: 1 PID: 7 Comm: kworker/u4:0 Not tainted 5.7.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: qrtr_ns_handler qrtr_ns_worker
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 radix_tree_deref_slot include/linux/radix-tree.h:176 [inline]
 radix_tree_deref_slot include/linux/radix-tree.h:174 [inline]
 ctrl_cmd_new_lookup+0x6eb/0x7e0 net/qrtr/ns.c:558
 qrtr_ns_worker+0x5a1/0x153a net/qrtr/ns.c:674
 process_one_work+0x965/0x16a0 kernel/workqueue.c:2268


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