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From: Arnd Bergmann <arnd@arndb.de>
To: Kulikov Vasiliy <segooon@gmail.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: kernel-janitors@vger.kernel.org, Neil Brown <neilb@suse.de>,
	Jens Axboe <jaxboe@fusionio.com>,
	linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] md: do not use ++ in rcu_dereference() argument
Date: Mon, 06 Sep 2010 20:10:55 +0000	[thread overview]
Message-ID: <201009062210.56824.arnd@arndb.de> (raw)
In-Reply-To: <1283711539-7123-1-git-send-email-segooon@gmail.com>

On Sunday 05 September 2010 20:32:18 Kulikov Vasiliy wrote:
> From: Vasiliy Kulikov <segooon@gmail.com>
> 
> rcu_dereference() is macro, so it might use its argument twice.
> Argument must not has side effects.
> 
> It was found by compiler warning:
> drivers/md/raid1.c: In function ‘read_balance’:
> drivers/md/raid1.c:445: warning: operation on ‘new_disk’ may be undefined

I think the rcu_dereference macro should really not evaluate its argument
twice, and I don't see where it does.
As a general rule, we try to write macros in Linux such that they behave
like functions and don't have surprising side-effects.

Which kernel and gcc version do you see the warning with?

	Arnd

WARNING: multiple messages have this Message-ID (diff)
From: Arnd Bergmann <arnd@arndb.de>
To: Kulikov Vasiliy <segooon@gmail.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: kernel-janitors@vger.kernel.org, Neil Brown <neilb@suse.de>,
	Jens Axboe <jaxboe@fusionio.com>,
	linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] md: do not use ++ in rcu_dereference() argument
Date: Mon, 6 Sep 2010 22:10:55 +0200	[thread overview]
Message-ID: <201009062210.56824.arnd@arndb.de> (raw)
In-Reply-To: <1283711539-7123-1-git-send-email-segooon@gmail.com>

On Sunday 05 September 2010 20:32:18 Kulikov Vasiliy wrote:
> From: Vasiliy Kulikov <segooon@gmail.com>
> 
> rcu_dereference() is macro, so it might use its argument twice.
> Argument must not has side effects.
> 
> It was found by compiler warning:
> drivers/md/raid1.c: In function ‘read_balance’:
> drivers/md/raid1.c:445: warning: operation on ‘new_disk’ may be undefined

I think the rcu_dereference macro should really not evaluate its argument
twice, and I don't see where it does.
As a general rule, we try to write macros in Linux such that they behave
like functions and don't have surprising side-effects.

Which kernel and gcc version do you see the warning with?

	Arnd
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WARNING: multiple messages have this Message-ID (diff)
From: Arnd Bergmann <arnd@arndb.de>
To: Kulikov Vasiliy <segooon@gmail.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: kernel-janitors@vger.kernel.org, Neil Brown <neilb@suse.de>,
	Jens Axboe <jaxboe@fusionio.com>,
	linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] md: do not use ++ in rcu_dereference() argument
Date: Mon, 6 Sep 2010 22:10:55 +0200	[thread overview]
Message-ID: <201009062210.56824.arnd@arndb.de> (raw)
In-Reply-To: <1283711539-7123-1-git-send-email-segooon@gmail.com>

On Sunday 05 September 2010 20:32:18 Kulikov Vasiliy wrote:
> From: Vasiliy Kulikov <segooon@gmail.com>
> 
> rcu_dereference() is macro, so it might use its argument twice.
> Argument must not has side effects.
> 
> It was found by compiler warning:
> drivers/md/raid1.c: In function ‘read_balance’:
> drivers/md/raid1.c:445: warning: operation on ‘new_disk’ may be undefined

I think the rcu_dereference macro should really not evaluate its argument
twice, and I don't see where it does.
As a general rule, we try to write macros in Linux such that they behave
like functions and don't have surprising side-effects.

Which kernel and gcc version do you see the warning with?

	Arnd

  parent reply	other threads:[~2010-09-06 20:10 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-09-05 18:32 [PATCH] md: do not use ++ in rcu_dereference() argument Kulikov Vasiliy
2010-09-05 18:32 ` Kulikov Vasiliy
2010-09-05 19:01 ` Sam Ravnborg
2010-09-05 19:01   ` Sam Ravnborg
2010-09-05 19:01   ` Sam Ravnborg
2010-09-05 19:23   ` Kulikov Vasiliy
2010-09-05 19:23     ` Kulikov Vasiliy
2010-09-05 19:23     ` Kulikov Vasiliy
2010-09-05 20:39     ` Sam Ravnborg
2010-09-05 20:39       ` Sam Ravnborg
2010-09-06  5:29       ` Neil Brown
2010-09-06  5:29         ` Neil Brown
2010-09-06  5:29         ` Neil Brown
2010-09-06  7:43         ` walter harms
2010-09-06  7:43           ` walter harms
2010-09-06 11:05           ` Neil Brown
2010-09-06 11:05             ` Neil Brown
2010-09-06 19:21         ` Sam Ravnborg
2010-09-06 19:21           ` Sam Ravnborg
2010-09-08  7:04           ` Neil Brown
2010-09-08  7:04             ` Neil Brown
2010-09-16 12:54         ` Avi Kivity
2010-09-16 12:54           ` Avi Kivity
2010-09-17  3:18           ` Neil Brown
2010-09-17  3:18             ` Neil Brown
2010-09-06 20:10 ` Arnd Bergmann [this message]
2010-09-06 20:10   ` Arnd Bergmann
2010-09-06 20:10   ` Arnd Bergmann
2010-09-07 19:21   ` Kulikov Vasiliy
2010-09-07 19:21     ` Kulikov Vasiliy
2010-09-07 19:21     ` Kulikov Vasiliy
2010-09-07 20:00     ` Arnd Bergmann
2010-09-07 20:00       ` Arnd Bergmann
2010-09-07 20:50       ` Paul E. McKenney
2010-09-07 20:50         ` Paul E. McKenney
2010-09-09 15:14         ` Arnd Bergmann
2010-09-09 15:14           ` Arnd Bergmann
2010-09-10  3:46           ` Paul E. McKenney
2010-09-10  3:46             ` Paul E. McKenney
2010-09-14  0:33             ` Paul E. McKenney
2010-09-14  0:33               ` Paul E. McKenney
2010-09-15 12:28               ` Arnd Bergmann
2010-09-15 12:28                 ` Arnd Bergmann
2010-09-16  6:15                 ` Paul E. McKenney
2010-09-16  6:15                   ` Paul E. McKenney

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