netdev - Re: [PATCH] netlink: allocate group bitmaps dynamically

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Date:	Tue, 03 Jul 2007 16:32:01 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	hadi@...erus.ca, Zhang Rui <rui.zhang@...el.com>,
	netdev@...r.kernel.org,
	"linux-acpi@...r" <linux-acpi@...r.kernel.org>, lenb@...nel.org,
	Thomas Graf <tgraf@...g.ch>
Subject: Re: [PATCH] netlink: allocate group bitmaps dynamically

On Tue, 2007-07-03 at 16:11 +0200, Patrick McHardy wrote:


> >>>-	nlk->groups = kzalloc(NLGRPSZ(groups), GFP_KERNEL);
> >>>-	if (nlk->groups == NULL)
> >>>+	if (nlk->ngroups >= groups)
> >>>+		return 0;
> >>>+
> >>>+	new_groups = krealloc(nlk->groups, NLGRPSZ(groups), GFP_KERNEL);
> >>>+	if (new_groups == NULL)
> >>> 		return -ENOMEM;
> >>>+	memset((char*)new_groups + NLGRPSZ(nlk->ngroups), 0,
> >>>+	       NLGRPSZ(groups) - NLGRPSZ(nlk->ngroups));
> >>>+	nlk->groups = new_groups;
> >>
> >>
> >>This should probably happen with the table grabbed to avoid races
> >>with concurrent broadcasts.
> > 
> > 
> > Hmm, possibly, I'll have to look again.
> 
> 
> do_one_broadcast locks the table and checks nlk->groups. The
> reallocation races with this without taking the lock or maybe
> using rcu.

Yeah, sounds about right, but since we lock the table anyway I see
little use in using RCU here. I'll look into it and also double-check
the first hunk of this patch.

johannes

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