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From: Oleg Nesterov <oleg@redhat.com>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: paulmck@kernel.org, peterz@infradead.org,
	linux-kernel@vger.kernel.org, rcu@vger.kernel.org,
	madhuparnabhowmik10@gmail.com, joel@joelfernandes.org,
	linux-kernel-mentees@lists.linuxfoundation.org, mingo@kernel.org
Subject: Re: [Linux-kernel-mentees] [PATCH] exit.c: Fix Sparse errors and warnings
Date: Thu, 30 Jan 2020 12:33:41 +0100	[thread overview]
Message-ID: <20200130113339.GA25426@redhat.com> (raw)
In-Reply-To: <20200130103158.azxldyfnugwvv6vy@wittgenstein>

On 01/30, Christian Brauner wrote:
>
> On Thu, Jan 30, 2020 at 11:50:28AM +0530, madhuparnabhowmik10@gmail.com wrote:
> > From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> >
> > This patch fixes the following sparse error:
> > kernel/exit.c:627:25: error: incompatible types in comparison expression
> >
> > And the following warning:
> > kernel/exit.c:626:40: warning: incorrect type in assignment
> >
> > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
>
> I think the previous version was already fine but hopefully
> RCU_INIT_POINTER() really saves some overhead. In any case:

It is not about overhead, RCU_INIT_POINTER() documents the fact that we
didn't make any changes to the new parent, we only need to change the
pointer.

And btw, I don't really understand the __rcu annotations. Say, according
to sparse this code is wrong:

	int __rcu *P;

	void func(int *p)
	{
		P = p;
	}

OK, although quite possibly it is fine.

However, this code

	int __rcu *P;

	void func(int __rcu *p)
	{
		*p = 10;
	       	P = p;
	}

is almost certainly wrong but sparse is happy, asn is the same.


> Acked-by: Christian Brauner <christian.brauner@ubuntu.com>

Acked-by: Oleg Nesterov <oleg@redhat.com>

_______________________________________________
Linux-kernel-mentees mailing list
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https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

WARNING: multiple messages have this Message-ID (diff)
From: Oleg Nesterov <oleg@redhat.com>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: madhuparnabhowmik10@gmail.com, peterz@infradead.org,
	mingo@kernel.org, paulmck@kernel.org,
	linux-kernel@vger.kernel.org, joel@joelfernandes.org,
	linux-kernel-mentees@lists.linuxfoundation.org,
	rcu@vger.kernel.org
Subject: Re: [PATCH] exit.c: Fix Sparse errors and warnings
Date: Thu, 30 Jan 2020 12:33:41 +0100	[thread overview]
Message-ID: <20200130113339.GA25426@redhat.com> (raw)
In-Reply-To: <20200130103158.azxldyfnugwvv6vy@wittgenstein>

On 01/30, Christian Brauner wrote:
>
> On Thu, Jan 30, 2020 at 11:50:28AM +0530, madhuparnabhowmik10@gmail.com wrote:
> > From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> >
> > This patch fixes the following sparse error:
> > kernel/exit.c:627:25: error: incompatible types in comparison expression
> >
> > And the following warning:
> > kernel/exit.c:626:40: warning: incorrect type in assignment
> >
> > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
>
> I think the previous version was already fine but hopefully
> RCU_INIT_POINTER() really saves some overhead. In any case:

It is not about overhead, RCU_INIT_POINTER() documents the fact that we
didn't make any changes to the new parent, we only need to change the
pointer.

And btw, I don't really understand the __rcu annotations. Say, according
to sparse this code is wrong:

	int __rcu *P;

	void func(int *p)
	{
		P = p;
	}

OK, although quite possibly it is fine.

However, this code

	int __rcu *P;

	void func(int __rcu *p)
	{
		*p = 10;
	       	P = p;
	}

is almost certainly wrong but sparse is happy, asn is the same.


> Acked-by: Christian Brauner <christian.brauner@ubuntu.com>

Acked-by: Oleg Nesterov <oleg@redhat.com>


  reply	other threads:[~2020-01-30 11:33 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-30  6:20 [Linux-kernel-mentees] [PATCH] exit.c: Fix Sparse errors and warnings madhuparnabhowmik10
2020-01-30  6:20 ` madhuparnabhowmik10
2020-01-30 10:31 ` [Linux-kernel-mentees] " Christian Brauner
2020-01-30 10:31   ` Christian Brauner
2020-01-30 11:33   ` Oleg Nesterov [this message]
2020-01-30 11:33     ` Oleg Nesterov
2020-01-30 11:45     ` [Linux-kernel-mentees] " Christian Brauner
2020-01-30 11:45       ` Christian Brauner
2020-01-30 15:20       ` [Linux-kernel-mentees] " Christian Brauner
2020-01-30 15:20         ` Christian Brauner
  -- strict thread matches above, loose matches on Subject: below --
2020-01-28 17:20 [Linux-kernel-mentees] " madhuparnabhowmik10
2020-01-28 18:01 ` Christian Brauner
2020-01-29 12:30 ` Oleg Nesterov
2020-01-29 16:02   ` Madhuparna Bhowmik

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