linux-kernel - Re: mmotm 2010-03-09-19-15: Lot of scheduling while atomic warnings related to RCU

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Date:	Thu, 11 Mar 2010 23:30:48 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Neil Horman <nhorman@...driver.com>
Cc:	Mel Gorman <mel@....ul.ie>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: mmotm 2010-03-09-19-15: Lot of scheduling while atomic warnings related to RCU

> a/lib/kobject_uevent.c~sysctl-fix-up-remaining-references-to-uevent_helper-fix
> +++ a/lib/kobject_uevent.c
> @@ -273,10 +273,11 @@ int kobject_uevent_env(struct kobject *k
>  #endif
> 
>         /* call uevent_helper, usually only enabled during early boot */
> +       rcu_read_lock();
>         helper = rcu_dereference(uevent_helper);
>         if (helper[0])
>                 retval = uevent_call_helper(subsystem, env);
> -
> +       rcu_read_unlock();
>  exit:

The data actually has to be copied, there's a helper for this in rcustring.
I'll try to send a patch later.

> loads/unloads while changing uevent_helper.  Anywho, should be easy to fix,
> Mel, can you modify the code to copy helper to a private variable, then unlock
> the rcu read side prior to calling uevent_call_helper?  I imagine that would be

Yes, except rcustring already has a helper for that :)

-Andi
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