Date:   Mon, 12 Feb 2018 07:54:48 -0800
From:   syzbot <syzbot+a0564419941aaae3fe3c@...kaller.appspotmail.com>
To:     davem@...emloft.net, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
        rds-devel@....oracle.com, santosh.shilimkar@...cle.com,
        syzkaller-bugs@...glegroups.com
Subject: WARNING: suspicious RCU usage in rds_tcp_conn_alloc

Hello,

syzbot hit the following crash on net-next commit
9a61df9e5f7471fe5be3e02bd0bed726b2761a54 (Sat Feb 10 03:32:41 2018 +0000)
Merge tag 'kbuild-v4.16-2' of  
git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild

So far this crash happened 910 times on net-next, upstream.
C reproducer is attached.
syzkaller reproducer is attached.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a0564419941aaae3fe3c@...kaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for  
details.
If you forward the report, please keep this part and the footer.


=============================
WARNING: suspicious RCU usage
4.15.0+ #222 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 syzkaller898803/4169:
  #0:  (rcu_read_lock){....}, at: [<0000000031b2c8b0>]  
__rds_conn_create+0xe46/0x1b50 net/rds/connection.c:218

stack backtrace:
CPU: 0 PID: 4169 Comm: syzkaller898803 Not tainted 4.15.0+ #222
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:00007ffe5faf3668 EFLAGS: 00000217 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00000000004a6a72 RCX: 00000000004451c9
RDX: 0000000000000000 RSI: 0000000020fc2000 RDI: 0000000000000004
RBP: 00007ffe5faf3788 R08: 000000002069affb R09: 0000000000000010
R10: 0000000000000000 R11: 0000000000000217 R12: 00007ffe5faf3788
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: 4169, name: syzkaller898803
1 lock held by syzkaller898803/4169:
  #0:  (rcu_read_lock){....}, at: [<0000000031b2c8b0>]  
__rds_conn_create+0xe46/0x1b50 net/rds/connection.c:218
CPU: 0 PID: 4169 Comm: syzkaller898803 Not tainted 4.15.0+ #222
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:00007ffe5faf3668 EFLAGS: 00000217 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00000000004a6a72 RCX: 00000000004451c9
RDX: 0000000000000000 RSI: 0000000020fc2000 RDI: 000000


---
This bug is generated by a dumb bot. It may contain errors.
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View attachment "raw.log.txt" of type "text/plain" (10874 bytes)

View attachment "repro.syz.txt" of type "text/plain" (940 bytes)

View attachment "repro.c.txt" of type "text/plain" (12163 bytes)

View attachment "config.txt" of type "text/plain" (136385 bytes)

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