=============================
WARNING: suspicious RCU usage
4.15.0+ #308 Not tainted
-----------------------------
./include/linux/rcupdate.h:302 Illegal context switch in RCU read-side critical section!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syzkaller323427/4166:
 #0:  (rcu_read_lock){....}, at: [<000000002882a5d6>] __rds_conn_create+0xe46/0x1b50 net/rds/connection.c:218

stack backtrace:
CPU: 0 PID: 4166 Comm: syzkaller323427 Not tainted 4.15.0+ #308
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 lockdep_rcu_suspicious+0x123/0x170 kernel/locking/lockdep.c:4592
 rcu_preempt_sleep_check include/linux/rcupdate.h:301 [inline]
 ___might_sleep+0x385/0x470 kernel/sched/core.c:6093
 __might_sleep+0x95/0x190 kernel/sched/core.c:6081
 slab_pre_alloc_hook mm/slab.h:420 [inline]
 slab_alloc mm/slab.c:3365 [inline]
 kmem_cache_alloc+0x2a2/0x760 mm/slab.c:3539
 rds_tcp_conn_alloc+0xa7/0x4e0 net/rds/tcp.c:296
 __rds_conn_create+0x112f/0x1b50 net/rds/connection.c:227
 rds_conn_create_outgoing+0x3f/0x50 net/rds/connection.c:309
 rds_sendmsg+0xda3/0x2390 net/rds/send.c:1126
 sock_sendmsg_nosec net/socket.c:630 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:640
 SYSC_sendto+0x361/0x5c0 net/socket.c:1747
 SyS_sendto+0x40/0x50 net/socket.c:1715
 do_syscall_64+0x282/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x26/0x9b
RIP: 0033:0x4451c9
RSP: 002b:00007ffe080c52f8 EFLAGS: 00000217 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00000000004a6a72 RCX: 00000000004451c9
RDX: 0000000000000000 RSI: 0000000020fc2000 RDI: 0000000000000004
RBP: 00007ffe080c5418 R08: 000000002069affb R09: 0000000000000010
R10: 0000000000000000 R11: 0000000000000217 R12: 00007ffe080c5418
R13: 0000000000402690 R14: 0000000000000000 R15: 0000000000000000
BUG: sleeping function called from invalid context at mm/slab.h:420
in_atomic(): 1, irqs_disabled(): 0, pid: 4166, name: syzkaller323427
1 lock held by syzkaller323427/4166:
 #0:  (rcu_read_lock){....}, at: [<000000002882a5d6>] __rds_conn_create+0xe46/0x1b50 net/rds/connection.c:218
CPU: 0 PID: 4166 Comm: syzkaller323427 Not tainted 4.15.0+ #308
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 ___might_sleep+0x2b2/0x470 kernel/sched/core.c:6128
 __might_sleep+0x95/0x190 kernel/sched/core.c:6081
 slab_pre_alloc_hook mm/slab.h:420 [inline]
 slab_alloc mm/slab.c:3365 [inline]
 kmem_cache_alloc+0x2a2/0x760 mm/slab.c:3539
 rds_tcp_conn_alloc+0xa7/0x4e0 net/rds/tcp.c:296
 __rds_conn_create+0x112f/0x1b50 net/rds/connection.c:227
 rds_conn_create_outgoing+0x3f/0x50 net/rds/connection.c:309
 rds_sendmsg+0xda3/0x2390 net/rds/send.c:1126
 sock_sendmsg_nosec net/socket.c:630 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:640
 SYSC_sendto+0x361/0x5c0 net/socket.c:1747
 SyS_sendto+0x40/0x50 net/socket.c:1715
 do_syscall_64+0x282/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x26/0x9b
RIP: 0033:0x4451c9
RSP: 002b:00007ffe080c52f8 EFLAGS: 00000217 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00000000004a6a72 RCX: 00000000004451c9
RDX: 0000000000000000 RSI: 0000000020fc2000 RDI: 0000000000000004
RBP: 00007ffe080c5418 R08: 000000002069affb R09: 0000000000000010
R10: 0000000000000000 R11: 0000000000000217 R12: 00007ffe080c5418
R13: 0000000000402690 R14: 0000000000000000 R15: 0000000000000000