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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Hugh Dickins <hughd@google.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	"Paul E. McKenney" <paul.mckenney@linaro.org>,
	linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: linux-next ppc64: RCU mods cause __might_sleep BUGs
Date: Thu, 03 May 2012 07:20:15 +1000	[thread overview]
Message-ID: <1335993615.4088.1.camel@pasglop> (raw)
In-Reply-To: <alpine.LSU.2.00.1205021324430.24246@eggly.anvils>

On Wed, 2012-05-02 at 13:25 -0700, Hugh Dickins wrote:
> Got it at last.  Embarrassingly obvious.  __rcu_read_lock() and
> __rcu_read_unlock() are not safe to be using __this_cpu operations,
> the cpu may change in between the rmw's read and write: they should
> be using this_cpu operations (or, I put preempt_disable/enable in the
> __rcu_read_unlock below).  __this_cpus there work out fine on x86,
> which was given good instructions to use; but not so well on PowerPC.
> 
> I've been running successfully for an hour now with the patch below;
> but I expect you'll want to consider the tradeoffs, and may choose a
> different solution.

Didn't Linus recently rant about these __this_cpu vs this_cpu nonsense ?

I thought that was going out..

Cheers,
Ben.



WARNING: multiple messages have this Message-ID (diff)
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Hugh Dickins <hughd@google.com>
Cc: "Paul E. McKenney" <paul.mckenney@linaro.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: linux-next ppc64: RCU mods cause __might_sleep BUGs
Date: Thu, 03 May 2012 07:20:15 +1000	[thread overview]
Message-ID: <1335993615.4088.1.camel@pasglop> (raw)
In-Reply-To: <alpine.LSU.2.00.1205021324430.24246@eggly.anvils>

On Wed, 2012-05-02 at 13:25 -0700, Hugh Dickins wrote:
> Got it at last.  Embarrassingly obvious.  __rcu_read_lock() and
> __rcu_read_unlock() are not safe to be using __this_cpu operations,
> the cpu may change in between the rmw's read and write: they should
> be using this_cpu operations (or, I put preempt_disable/enable in the
> __rcu_read_unlock below).  __this_cpus there work out fine on x86,
> which was given good instructions to use; but not so well on PowerPC.
> 
> I've been running successfully for an hour now with the patch below;
> but I expect you'll want to consider the tradeoffs, and may choose a
> different solution.

Didn't Linus recently rant about these __this_cpu vs this_cpu nonsense ?

I thought that was going out..

Cheers,
Ben.

  parent reply	other threads:[~2012-05-02 21:22 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-04-30 22:37 linux-next ppc64: RCU mods cause __might_sleep BUGs Hugh Dickins
2012-04-30 22:37 ` Hugh Dickins
2012-04-30 23:14 ` Paul E. McKenney
2012-04-30 23:14   ` Paul E. McKenney
2012-05-01  0:33 ` Benjamin Herrenschmidt
2012-05-01  0:33   ` Benjamin Herrenschmidt
2012-05-01  5:10   ` Hugh Dickins
2012-05-01  5:10     ` Hugh Dickins
2012-05-01 14:22     ` Paul E. McKenney
2012-05-01 14:22       ` Paul E. McKenney
2012-05-01 21:42       ` Hugh Dickins
2012-05-01 21:42         ` Hugh Dickins
2012-05-01 23:25         ` Paul E. McKenney
2012-05-01 23:25           ` Paul E. McKenney
2012-05-02 20:25           ` Hugh Dickins
2012-05-02 20:25             ` Hugh Dickins
2012-05-02 20:49             ` Paul E. McKenney
2012-05-02 20:49               ` Paul E. McKenney
2012-05-02 21:32               ` Paul E. McKenney
2012-05-02 21:32                 ` Paul E. McKenney
2012-05-02 21:36                 ` Paul E. McKenney
2012-05-02 21:36                   ` Paul E. McKenney
2012-05-02 21:20             ` Benjamin Herrenschmidt [this message]
2012-05-02 21:20               ` Benjamin Herrenschmidt
2012-05-02 21:54               ` Paul E. McKenney
2012-05-02 21:54                 ` Paul E. McKenney
2012-05-02 22:54                 ` Hugh Dickins
2012-05-02 22:54                   ` Hugh Dickins
2012-05-03  0:14                   ` Paul E. McKenney
2012-05-03  0:14                     ` Paul E. McKenney
2012-05-03  0:24                     ` Hugh Dickins
2012-05-03  0:24                       ` Hugh Dickins
2012-05-07 16:21                       ` Hugh Dickins
2012-05-07 16:21                         ` Hugh Dickins
2012-05-07 18:50                         ` Paul E. McKenney
2012-05-07 18:50                           ` Paul E. McKenney
2012-05-07 21:38                           ` Hugh Dickins
2012-05-07 21:38                             ` Hugh Dickins
2012-05-01 13:39   ` Paul E. McKenney
2012-05-01 13:39     ` Paul E. McKenney

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