linux-kernel - Re: [PATCH tip/core/rcu 03/17] signal: Explain local_irq

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <53BBB37F.6030807@cn.fujitsu.com>
Date:	Tue, 8 Jul 2014 17:01:51 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
CC:	<linux-kernel@...r.kernel.org>, <mingo@...nel.org>,
	<dipankar@...ibm.com>, <akpm@...ux-foundation.org>,
	<mathieu.desnoyers@...icios.com>, <josh@...htriplett.org>,
	<niv@...ibm.com>, <tglx@...utronix.de>, <peterz@...radead.org>,
	<rostedt@...dmis.org>, <dhowells@...hat.com>,
	<edumazet@...gle.com>, <dvhart@...ux.intel.com>,
	<fweisbec@...il.com>, <oleg@...hat.com>, <sbw@....edu>
Subject: Re: [PATCH tip/core/rcu 03/17] signal: Explain local_irq_save() call

On 07/08/2014 06:38 AM, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> 
> The explicit local_irq_save() in __lock_task_sighand() is needed to avoid
> a potential deadlock condition, as noted in a841796f11c90d53 (signal:
> align __lock_task_sighand() irq disabling and RCU).  However, someone
> reading the code might be forgiven for concluding that this separate
> local_irq_save() was completely unnecessary.  This commit therefore adds
> a comment referencing the shiny new block comment on rcu_read_unlock().
> 
> Reported-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Acked-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/signal.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/signal.c b/kernel/signal.c
> index a4077e90f19f..46161e744760 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1263,6 +1263,10 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
>  	struct sighand_struct *sighand;
>  
>  	for (;;) {
> +		/*
> +		 * Disable interrupts early to avoid deadlocks.
> +		 * See rcu_read_unlock comment header for details.
> +		 */

A pair of brackets are missing here: rcu_read_unlock()
after that, please add:

Reviewed-by: Lai Jiangshan <laijs@...fujitsu.com>


It reminds me that I should keep my effort to solve the deadlock
problem where rcu_read_unlock() is overlapped with schedule locks.

>  		local_irq_save(*flags);
>  		rcu_read_lock();
>  		sighand = rcu_dereference(tsk->sighand);

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/