> -----Original Message----- > From: Alexei Starovoitov [mailto:alexei.starovoitov@xxxxxxxxx] > Sent: Friday, March 3, 2023 3:04 PM > To: John Fastabend <john.fastabend@xxxxxxxxx> > Cc: liujian (CE) <liujian56@xxxxxxxxxx>; Eric Dumazet > <edumazet@xxxxxxxxxx>; Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>; David S. > Miller <davem@xxxxxxxxxxxxx>; David Ahern <dsahern@xxxxxxxxxx>; Jakub > Kicinski <kuba@xxxxxxxxxx>; Paolo Abeni <pabeni@xxxxxxxxxx>; Alexei > Starovoitov <ast@xxxxxxxxxx>; Cong Wang <cong.wang@xxxxxxxxxxxxx>; > Daniel Borkmann <daniel@xxxxxxxxxxxxx>; Network Development > <netdev@xxxxxxxxxxxxxxx>; bpf <bpf@xxxxxxxxxxxxxxx> > Subject: Re: [PATCH bpf] bpf, sockmap: fix an infinite loop error when len is 0 > in tcp_bpf_recvmsg_parser() > > On Tue, Feb 28, 2023 at 12:36 AM John Fastabend > <john.fastabend@xxxxxxxxx> wrote: > > > > Liu Jian wrote: > > > When the buffer length of the recvmsg system call is 0, we got the > > > flollowing soft lockup problem: > > > > > > watchdog: BUG: soft lockup - CPU#3 stuck for 27s! [a.out:6149] > > > CPU: 3 PID: 6149 Comm: a.out Kdump: loaded Not tainted 6.2.0+ #30 > > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 > > > 04/01/2014 > > > RIP: 0010:remove_wait_queue+0xb/0xc0 > > > Code: 5e 41 5f c3 cc cc cc cc 0f 1f 80 00 00 00 00 90 90 90 90 90 90 > > > 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 41 57 <41> > > > 56 41 55 41 54 55 48 89 fd 53 48 89 f3 4c 8d 6b 18 4c 8d 73 20 > > > RSP: 0018:ffff88811b5978b8 EFLAGS: 00000246 > > > RAX: 0000000000000000 RBX: ffff88811a7d3780 RCX: ffffffffb7a4d768 > > > RDX: dffffc0000000000 RSI: ffff88811b597908 RDI: ffff888115408040 > > > RBP: 1ffff110236b2f1b R08: 0000000000000000 R09: ffff88811a7d37e7 > > > R10: ffffed10234fa6fc R11: 0000000000000001 R12: ffff88811179b800 > > > R13: 0000000000000001 R14: ffff88811a7d38a8 R15: ffff88811a7d37e0 > > > FS: 00007f6fb5398740(0000) GS:ffff888237180000(0000) > > > knlGS:0000000000000000 > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > CR2: 0000000020000000 CR3: 000000010b6ba002 CR4: 0000000000370ee0 > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > > Call Trace: > > > <TASK> > > > tcp_msg_wait_data+0x279/0x2f0 > > > tcp_bpf_recvmsg_parser+0x3c6/0x490 > > > inet_recvmsg+0x280/0x290 > > > sock_recvmsg+0xfc/0x120 > > > ____sys_recvmsg+0x160/0x3d0 > > > ___sys_recvmsg+0xf0/0x180 > > > __sys_recvmsg+0xea/0x1a0 > > > do_syscall_64+0x3f/0x90 > > > entry_SYSCALL_64_after_hwframe+0x72/0xdc > > > > > > The logic in tcp_bpf_recvmsg_parser is as follows: > > > > > > msg_bytes_ready: > > > copied = sk_msg_recvmsg(sk, psock, msg, len, flags); > > > if (!copied) { > > > wait data; > > > goto msg_bytes_ready; > > > } > > > > > > In this case, "copied" alway is 0, the infinite loop occurs. > > > > > > According to the Linux system call man page, 0 should be returned in > > > this case. Therefore, in tcp_bpf_recvmsg_parser(), if the length is > > > 0, directly return. > > > > > > Also modify several other functions with the same problem. > > > > > > Fixes: 1f5be6b3b063 ("udp: Implement udp_bpf_recvmsg() for sockmap") > > > Fixes: 9825d866ce0d ("af_unix: Implement unix_dgram_bpf_recvmsg()") > > > Fixes: c5d2177a72a1 ("bpf, sockmap: Fix race in ingress receive > > > verdict with redirect to self") > > > Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg > > > interface") > > > Signed-off-by: Liu Jian <liujian56@xxxxxxxxxx> > > > --- > > > > Thanks. > > > > Acked-by: John Fastabend <john.fastabend@xxxxxxxxx> > > Thanks John. > > Liu, > > could you please change if (len == 0) to if (!len) and respin with John's ack. > Thanks Okay, I will send v2. Thanks.
