linux-kernel - Re: [PATCH v27 04/12] LRNG - add switchable DRNG support

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Date:   Sun, 12 Jan 2020 11:12:49 +0100
From:   Stephan Müller <smueller@...onox.de>
To:     kbuild test robot <lkp@...el.com>
Cc:     kbuild-all@...ts.01.org, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        "Theodore Y. Ts'o" <tytso@....edu>, Willy Tarreau <w@....eu>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Vito Caputo <vcaputo@...garu.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>, Ray Strode <rstrode@...hat.com>,
        William Jon McCann <mccann@....edu>,
        zhangjs <zachary@...shancloud.com>,
        Andy Lutomirski <luto@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        Nicolai Stange <nstange@...e.de>,
        "Peter, Matthias" <matthias.peter@....bund.de>,
        Marcelo Henrique Cerri <marcelo.cerri@...onical.com>,
        Roman Drahtmueller <draht@...altsekun.de>,
        Neil Horman <nhorman@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Julia Lawall <julia.lawall@...ia.fr>
Subject: Re: [PATCH v27 04/12] LRNG - add switchable DRNG support

Am Samstag, 11. Januar 2020, 08:09:50 CET schrieb kbuild test robot:

Hi,

> Hi "Stephan,
> 
> Thank you for the patch! Perhaps something to improve:
> 
> [auto build test WARNING on char-misc/char-misc-testing]
> [also build test WARNING on cryptodev/master crypto/master v5.5-rc5
> next-20200110] [if your patch is applied to the wrong git tree, please drop
> us a note to help improve the system. BTW, we also suggest to use '--base'
> option to specify the base tree in git format-patch, please see
> https://stackoverflow.com/a/37406982]
> 
> url:   
> https://github.com/0day-ci/linux/commits/Stephan-M-ller/dev-random-a-new-ap
> proach-with-full-SP800-90B/20200110-084934 base:  
> https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
> 68faa679b8be1a74e6663c21c3a9d25d32f1c079 reproduce:
>         # apt-get install sparse
>         # sparse version: v0.6.1-129-g341daf20-dirty
>         make ARCH=x86_64 allmodconfig
>         make C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'
> 
> If you fix the issue, kindly add following tag
> Reported-by: kbuild test robot <lkp@...el.com>
> 
> 
> sparse warnings: (new ones prefixed by >>)
> 
> >> drivers/char/lrng/lrng_internal.h:239:39: sparse: sparse: context
> >> imbalance in 'lrng_drng_switch' - unexpected unlock
> vim +/lrng_drng_switch +239 drivers/char/lrng/lrng_internal.h
> 
> 58c283819a1e87 Stephan Müller 2020-01-09  233
> 58c283819a1e87 Stephan Müller 2020-01-09  234  /* Unlock the DRNG */
> 58c283819a1e87 Stephan Müller 2020-01-09  235  static __always_inline void
> lrng_drng_unlock(struct lrng_drng *drng, 58c283819a1e87 Stephan Müller
> 2020-01-09  236  					     unsigned long *flags) 
58c283819a1e87 Stephan
> Müller 2020-01-09  237  {
> 58c283819a1e87 Stephan Müller 2020-01-09  238  	if
> (lrng_drng_is_atomic(drng)) 58c283819a1e87 Stephan Müller 2020-01-09 @239 
> 		spin_unlock_irqrestore(&drng->spin_lock, *flags); 58c283819a1e87 
Stephan
> Müller 2020-01-09  240  	else
> 58c283819a1e87 Stephan Müller 2020-01-09  241  		mutex_unlock(&drng-
>lock);
> 58c283819a1e87 Stephan Müller 2020-01-09  242  }
> 58c283819a1e87 Stephan Müller 2020-01-09  243
> 
> :::::: The code at line 239 was first introduced by commit
> :::::: 58c283819a1e879bc2e30d05720285f9709f7f6d Linux Random Number
> :::::: Generator
> :::::: 
> :::::: TO: Stephan Müller <smueller@...onox.de>
> :::::: CC: 0day robot <lkp@...el.com>
> 
> ---
> 0-DAY kernel test infrastructure                 Open Source Technology
> Center https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org Intel
> Corporation

After analyzing the issue a bit more, it seems that I have to remove 
"unlikely" from lrng_drng_lock which seems to cause additional grief
with sparse. Note, sparse will still report a lock context imbalance as it
used to since we indeed have two lock context as documented in
lrng_drng_switch.

Ciao
Stephan