netdev - Re: INFO: rcu detected stall in vprintk

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Date:   Mon, 25 Jun 2018 22:59:37 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     syzbot <syzbot+d29d18215e477cfbfbdd@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org, pmladek@...e.com,
        sergey.senozhatsky@...il.com, syzkaller-bugs@...glegroups.com,
        Samuel Ortiz <sameo@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: INFO: rcu detected stall in vprintk_emit

On Tue, 26 Jun 2018 10:49:24 +0900
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> wrote:

> So we can try switching to ratelimited error reporting
> [that would be option A]:
> 
> ---
> 
> diff --git a/net/nfc/llcp_commands.c b/net/nfc/llcp_commands.c
> index 2ceefa183cee..2f3becb709b8 100644
> --- a/net/nfc/llcp_commands.c
> +++ b/net/nfc/llcp_commands.c
> @@ -755,7 +755,7 @@ int nfc_llcp_send_ui_frame(struct nfc_llcp_sock *sock, u8 ssap, u8 dsap,
>  		pdu = nfc_alloc_send_skb(sock->dev, &sock->sk, MSG_DONTWAIT,
>  					 frag_len + LLCP_HEADER_SIZE, &err);
>  		if (pdu == NULL) {
> -			pr_err("Could not allocate PDU\n");
> +			pr_err_ratelimited("Could not allocate PDU\n");
>  			continue;
>  		}
>  
> ---
> 
> 
> Or ratelimited error reporting and cond_resched()
> [that would be option B]:

I don't think this is a printk() issue per se, so I think Option B is
the only option. You should not get stuck in an infinite loop if we run
short on memory. Perhaps we could have an Option C which would exit
this loop gracefully with some kind of error. But I haven't looked at
the surrounding code to be sure if that is possible.

-- Steve

> 
> ---
> 
> diff --git a/net/nfc/llcp_commands.c b/net/nfc/llcp_commands.c
> index 2ceefa183cee..61741db4c4e6 100644
> --- a/net/nfc/llcp_commands.c
> +++ b/net/nfc/llcp_commands.c
> @@ -755,7 +755,8 @@ int nfc_llcp_send_ui_frame(struct nfc_llcp_sock *sock, u8 ssap, u8 dsap,
>  		pdu = nfc_alloc_send_skb(sock->dev, &sock->sk, MSG_DONTWAIT,
>  					 frag_len + LLCP_HEADER_SIZE, &err);
>  		if (pdu == NULL) {
> -			pr_err("Could not allocate PDU\n");
> +			pr_err_ratelimited("Could not allocate PDU\n");
> +			cond_resched();
>  			continue;
>  		}
>  
> ---