netdev - Re: [PATCH net] sctp: avoid running the sctp state machine recursively

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Message-Id: <20190501.091948.243588960568894414.davem@davemloft.net>
Date:   Wed, 01 May 2019 09:19:48 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     lucien.xin@...il.com
Cc:     netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
        marcelo.leitner@...il.com, nhorman@...driver.com
Subject: Re: [PATCH net] sctp: avoid running the sctp state machine
 recursively

From: Xin Long <lucien.xin@...il.com>
Date: Mon, 29 Apr 2019 14:16:19 +0800

> Ying triggered a call trace when doing an asconf testing:
 ...
> As it shows, the first sctp_do_sm() running under atomic context (NET_RX
> softirq) invoked sctp_primitive_ASCONF() that uses GFP_KERNEL flag later,
> and this flag is supposed to be used in non-atomic context only. Besides,
> sctp_do_sm() was called recursively, which is not expected.
> 
> Vlad tried to fix this recursive call in Commit c0786693404c ("sctp: Fix
> oops when sending queued ASCONF chunks") by introducing a new command
> SCTP_CMD_SEND_NEXT_ASCONF. But it didn't work as this command is still
> used in the first sctp_do_sm() call, and sctp_primitive_ASCONF() will
> be called in this command again.
> 
> To avoid calling sctp_do_sm() recursively, we send the next queued ASCONF
> not by sctp_primitive_ASCONF(), but by sctp_sf_do_prm_asconf() in the 1st
> sctp_do_sm() directly.
> 
> Reported-by: Ying Xu <yinxu@...hat.com>
> Signed-off-by: Xin Long <lucien.xin@...il.com>

Applied and queued up for -stable.