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Subject[PATCH 5.5 038/151] net: memcg: fix lockdep splat in inet_csk_accept()
Date
From: Eric Dumazet <edumazet@google.com>

commit 06669ea346e476a5339033d77ef175566a40efbb upstream.

Locking newsk while still holding the listener lock triggered
a lockdep splat [1]

We can simply move the memcg code after we release the listener lock,
as this can also help if multiple threads are sharing a common listener.

Also fix a typo while reading socket sk_rmem_alloc.

[1]
WARNING: possible recursive locking detected
5.6.0-rc3-syzkaller #0 Not tainted
--------------------------------------------
syz-executor598/9524 is trying to acquire lock:
ffff88808b5b8b90 (sk_lock-AF_INET6){+.+.}, at: lock_sock include/net/sock.h:1541 [inline]
ffff88808b5b8b90 (sk_lock-AF_INET6){+.+.}, at: inet_csk_accept+0x69f/0xd30 net/ipv4/inet_connection_sock.c:492

but task is already holding lock:
ffff88808b5b9590 (sk_lock-AF_INET6){+.+.}, at: lock_sock include/net/sock.h:1541 [inline]
ffff88808b5b9590 (sk_lock-AF_INET6){+.+.}, at: inet_csk_accept+0x8d/0xd30 net/ipv4/inet_connection_sock.c:445

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(sk_lock-AF_INET6);
lock(sk_lock-AF_INET6);

*** DEADLOCK ***

May be due to missing lock nesting notation

1 lock held by syz-executor598/9524:
#0: ffff88808b5b9590 (sk_lock-AF_INET6){+.+.}, at: lock_sock include/net/sock.h:1541 [inline]
#0: ffff88808b5b9590 (sk_lock-AF_INET6){+.+.}, at: inet_csk_accept+0x8d/0xd30 net/ipv4/inet_connection_sock.c:445

stack backtrace:
CPU: 0 PID: 9524 Comm: syz-executor598 Not tainted 5.6.0-rc3-syzkaller #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+0x188/0x20d lib/dump_stack.c:118
print_deadlock_bug kernel/locking/lockdep.c:2370 [inline]
check_deadlock kernel/locking/lockdep.c:2411 [inline]
validate_chain kernel/locking/lockdep.c:2954 [inline]
__lock_acquire.cold+0x114/0x288 kernel/locking/lockdep.c:3954
lock_acquire+0x197/0x420 kernel/locking/lockdep.c:4484
lock_sock_nested+0xc5/0x110 net/core/sock.c:2947
lock_sock include/net/sock.h:1541 [inline]
inet_csk_accept+0x69f/0xd30 net/ipv4/inet_connection_sock.c:492
inet_accept+0xe9/0x7c0 net/ipv4/af_inet.c:734
__sys_accept4_file+0x3ac/0x5b0 net/socket.c:1758
__sys_accept4+0x53/0x90 net/socket.c:1809
__do_sys_accept4 net/socket.c:1821 [inline]
__se_sys_accept4 net/socket.c:1818 [inline]
__x64_sys_accept4+0x93/0xf0 net/socket.c:1818
do_syscall_64+0xf6/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4445c9
Code: e8 0c 0d 03 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 eb 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffc35b37608 EFLAGS: 00000246 ORIG_RAX: 0000000000000120
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004445c9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000306777 R09: 0000000000306777
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00000000004053d0 R14: 0000000000000000 R15: 0000000000000000

Fixes: d752a4986532 ("net: memcg: late association of sock to memcg")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Shakeel Butt <shakeelb@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/inet_connection_sock.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)

--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -483,27 +483,27 @@ struct sock *inet_csk_accept(struct sock
spin_unlock_bh(&queue->fastopenq.lock);
}

- if (mem_cgroup_sockets_enabled) {
+out:
+ release_sock(sk);
+ if (newsk && mem_cgroup_sockets_enabled) {
int amt;

/* atomically get the memory usage, set and charge the
- * sk->sk_memcg.
+ * newsk->sk_memcg.
*/
lock_sock(newsk);

- /* The sk has not been accepted yet, no need to look at
- * sk->sk_wmem_queued.
+ /* The socket has not been accepted yet, no need to look at
+ * newsk->sk_wmem_queued.
*/
amt = sk_mem_pages(newsk->sk_forward_alloc +
- atomic_read(&sk->sk_rmem_alloc));
+ atomic_read(&newsk->sk_rmem_alloc));
mem_cgroup_sk_alloc(newsk);
if (newsk->sk_memcg && amt)
mem_cgroup_charge_skmem(newsk->sk_memcg, amt);

release_sock(newsk);
}
-out:
- release_sock(sk);
if (req)
reqsk_put(req);
return newsk;

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