linux-kernel - Re: net/kcm/kcmsock.c:645 kcm_write_msgs() error: we previously assumed 'psock' could be null (see line 585)

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Date:   Tue, 25 Jan 2022 17:11:20 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        "kbuild@...ts.01.org" <kbuild@...ts.01.org>
CC:     "lkp@...el.com" <lkp@...el.com>,
        "kbuild-all@...ts.01.org" <kbuild-all@...ts.01.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: net/kcm/kcmsock.c:645 kcm_write_msgs() error: we previously
 assumed 'psock' could be null (see line 585)



Le 25/01/2022 à 15:47, Dan Carpenter a écrit :
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   9b57f458985742bd1c585f4c7f36d04634ce1143
> commit: 1e688dd2a3d6759d416616ff07afc4bb836c4213 powerpc/bug: Provide better flexibility to WARN_ON/__WARN_FLAGS() with asm goto
> config: powerpc64-randconfig-m031-20220120 (https://download.01.org/0day-ci/archive/20220122/202201220354.fJ3VzqBt-lkp@intel.com/config)
> compiler: powerpc64-linux-gcc (GCC) 11.2.0
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@...el.com>
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> 
> smatch warnings:
> net/kcm/kcmsock.c:645 kcm_write_msgs() error: we previously assumed 'psock' could be null (see line 585)
> 
> vim +/psock +645 net/kcm/kcmsock.c
> 
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  589  		unreserve_psock(kcm);
> cd6e111bf5be5c7 Tom Herbert             2016-03-07  590  		kcm_report_tx_retry(kcm);
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  591  		if (skb_queue_empty(&sk->sk_write_queue))
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  592  			return 0;
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  593
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  594  		kcm_tx_msg(skb_peek(&sk->sk_write_queue))->sent = 0;
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  595
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  596  	} else if (skb_queue_empty(&sk->sk_write_queue)) {
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  597  		return 0;
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  598  	}
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  599
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  600  	head = skb_peek(&sk->sk_write_queue);
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  601  	txm = kcm_tx_msg(head);
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  602
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  603  	if (txm->sent) {
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  604  		/* Send of first skbuff in queue already in progress */
> ab7ac4eb9832e32 Tom Herbert             2016-03-07  605  		if (WARN_ON(!psock)) {
> 
> This warning is a false positive.
> 
> The new Power PC implementation of WARN_ON() is written in asm and
> Smatch can only parse C.  I don't have a cross compile system set up so
> fixing this is going to be a big headache.  :/

Can you explain what the problem is ?

Yes psock could be NULL, that the reason why there is this WARN_ON(), 
isn't it ?
So what does smatch doesn't like here ?

How do I install smatch and how do I use it to reproduce that ?

Is it like sparse, does it set the __CHECKER__ macro ? Would it work if 
we do a simplified C version of WARN_ON() when __CHECKER__ is defined ?

Thanks
Christophe