linux-kernel - RE: [PATCH] staging: lustre: add error handling for try_module

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Date:   Wed, 13 Jun 2018 10:53:07 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Zhouyang Jia' <jiazhouyang09@...il.com>
CC:     Oleg Drokin <oleg.drokin@...el.com>,
        Andreas Dilger <andreas.dilger@...el.com>,
        James Simmons <jsimmons@...radead.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        NeilBrown <neilb@...e.com>,
        Haneen Mohammed <hamohammed.sa@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>,
        "lustre-devel@...ts.lustre.org" <lustre-devel@...ts.lustre.org>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] staging: lustre: add error handling for try_module_get

From: Zhouyang Jia
> Sent: 12 June 2018 05:49
> 
> When try_module_get fails, the lack of error-handling code may
> cause unexpected results.
> 
> This patch adds error-handling code after calling try_module_get.
...
> +++ b/drivers/staging/lustre/lnet/klnds/socklnd/socklnd.c
> @@ -2422,7 +2422,10 @@ ksocknal_base_startup(void)
> 
>  	/* flag lists/ptrs/locks initialised */
>  	ksocknal_data.ksnd_init = SOCKNAL_INIT_DATA;
> -	try_module_get(THIS_MODULE);
> +	if (!try_module_get(THIS_MODULE)) {
> +		CERROR("%s: cannot get module\n", __func__);
> +		goto failed;
> +	}


Can try_module_get(THIS_MODULE) ever fail?
Since you are running code in 'THIS_MODULE' the caller must have a
reference that can't go away.
So try_module_get() just increments the count that is already greater
than zero.

Similarly module_put(THIS_MODULE) must never be able to release the
last reference.
Any such calls that aren't in error paths after try_module_get() are
probably buggy.

	David