Messages in this thread | | | From | Eric Dumazet <> | Date | Mon, 6 Jun 2022 10:31:49 -0700 | Subject | Re: [PATCH net-next] ax25: Fix deadlock caused by skb_recv_datagram in ax25_recvmsg |
| |
On Mon, Jun 6, 2022 at 9:21 AM Duoming Zhou <duoming@zju.edu.cn> wrote: > > The skb_recv_datagram() in ax25_recvmsg() will hold lock_sock > and block until it receives a packet from the remote. If the client > doesn`t connect to server and calls read() directly, it will not > receive any packets forever. As a result, the deadlock will happen. > > The fail log caused by deadlock is shown below: > > [ 861.122612] INFO: task ax25_deadlock:148 blocked for more than 737 seconds. > [ 861.124543] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > [ 861.127764] Call Trace: > [ 861.129688] <TASK> > [ 861.130743] __schedule+0x2f9/0xb20 > [ 861.131526] schedule+0x49/0xb0 > [ 861.131640] __lock_sock+0x92/0x100 > [ 861.131640] ? destroy_sched_domains_rcu+0x20/0x20 > [ 861.131640] lock_sock_nested+0x6e/0x70 > [ 861.131640] ax25_sendmsg+0x46/0x420 > [ 861.134383] ? ax25_recvmsg+0x1e0/0x1e0 > [ 861.135658] sock_sendmsg+0x59/0x60 > [ 861.136791] __sys_sendto+0xe9/0x150 > [ 861.137212] ? __schedule+0x301/0xb20 > [ 861.137710] ? __do_softirq+0x4a2/0x4fd > [ 861.139153] __x64_sys_sendto+0x20/0x30 > [ 861.140330] do_syscall_64+0x3b/0x90 > [ 861.140731] entry_SYSCALL_64_after_hwframe+0x46/0xb0 > [ 861.141249] RIP: 0033:0x7fdf05ee4f64 > [ 861.141249] RSP: 002b:00007ffe95772fc0 EFLAGS: 00000246 ORIG_RAX: 000000000000002c > [ 861.141249] RAX: ffffffffffffffda RBX: 0000565303a013f0 RCX: 00007fdf05ee4f64 > [ 861.141249] RDX: 0000000000000005 RSI: 0000565303a01678 RDI: 0000000000000005 > [ 861.141249] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 > [ 861.141249] R10: 0000000000000000 R11: 0000000000000246 R12: 0000565303a00cf0 > [ 861.141249] R13: 00007ffe957730e0 R14: 0000000000000000 R15: 0000000000000000 > > This patch moves the skb_recv_datagram() before lock_sock() in order > that other functions that need lock_sock could be executed. >
Why is this targeting net-next tree ?
1) A fix should target net tree 2) It should include a Fixes: tag
Also: - this patch bypasses tests in ax25_recvmsg() - This might break applications depending on blocking read() operations.
I feel a real fix is going to be slightly more difficult than that.
Thank you
> Reported-by: Thomas Habets <thomas@@habets.se> > Signed-off-by: Duoming Zhou <duoming@zju.edu.cn> > --- > net/ax25/af_ax25.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c > index 95393bb2760..02cd6087512 100644 > --- a/net/ax25/af_ax25.c > +++ b/net/ax25/af_ax25.c > @@ -1665,6 +1665,11 @@ static int ax25_recvmsg(struct socket *sock, struct msghdr *msg, size_t size, > int copied; > int err = 0; > > + /* Now we can treat all alike */ > + skb = skb_recv_datagram(sk, flags, &err); > + if (!skb) > + goto done; > + > lock_sock(sk); > /* > * This works for seqpacket too. The receiver has ordered the > @@ -1675,11 +1680,6 @@ static int ax25_recvmsg(struct socket *sock, struct msghdr *msg, size_t size, > goto out; > } > > - /* Now we can treat all alike */ > - skb = skb_recv_datagram(sk, flags, &err); > - if (skb == NULL) > - goto out; > - > if (!sk_to_ax25(sk)->pidincl) > skb_pull(skb, 1); /* Remove PID */ > > @@ -1725,6 +1725,7 @@ static int ax25_recvmsg(struct socket *sock, struct msghdr *msg, size_t size, > out: > release_sock(sk); > > +done: > return err; > } > > -- > 2.17.1 >
| |