linux-kernel - Re: [PATCH] Fix sched_domain sysctl registration again

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Message-ID: <20071021074301.GA14368@elte.hu>
Date:	Sun, 21 Oct 2007 09:43:01 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Milton D. Miller II" <miltonm@...ltime.net>
Cc:	Paul Jackson <pj@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix sched_domain sysctl registration again


* Milton D. Miller II <miltonm@...ltime.net> wrote:

> commit 029190c515f15f512ac85de8fc686d4dbd0ae731 (cpuset 
> sched_load_balance flag) was not tested SCHED_DEBUG enabled as 
> committed as it dereferences NULL when used and it reordered the 
> sysctl registration to cause it to never show any domains or their 
> tunables.
> 
> Fixes:
> 
> 1) restore arch_init_sched_domains ordering
> 	we can't walk the domains before we build them
> 
> 	presently we register cpus with empty directories (no domain
> 	directories or files).
> 
> 2) make unregister_sched_domain_sysctl do nothing when already unregistered
> 	detach_destroy_domains is now called one set of cpus at a time
> 	unregister_syctl dereferences NULL if called with a null.
> 
> 	While the the function would always dereference null if called
> 	twice, in the previous code it was always called once and then
> 	was followed a register.  So only the hidden bug of the
> 	sysctl_root_table not being allocated followed by an attempt to
> 	free it would have shown the error.
> 
> 3) always call unregister and register in partition_sched_domains
> 	The code is "smart" about unregistering only needed domains.
> 	Since we aren't guaranteed any calls to unregister, always 
> 	unregister.   Without calling register on the way out we
> 	will not have a table or any sysctl tree.
> 
> 4) warn if register is called without unregistering
> 	The previous table memory is lost, leaving pointers to the
> 	later freed memory in sysctl and leaking the memory of the
> 	tables.

thanks, applied.

	Ingo
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