netdev - RE: [patch] ixgbevf: potential NULL dereference on allocation failure

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Date:	Fri, 10 Sep 2010 13:25:11 -0700
From:	"Rose, Gregory V" <gregory.v.rose@...el.com>
To:	David Miller <davem@...emloft.net>,
	"error27@...il.com" <error27@...il.com>
CC:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: RE: [patch] ixgbevf: potential NULL dereference on allocation
 failure

>-----Original Message-----
>From: David Miller [mailto:davem@...emloft.net]
>Sent: Friday, September 10, 2010 1:22 PM
>To: error27@...il.com
>Cc: Rose, Gregory V; Kirsher, Jeffrey T; netdev@...r.kernel.org; kernel-
>janitors@...r.kernel.org
>Subject: Re: [patch] ixgbevf: potential NULL dereference on allocation
>failure
>
>It's trying to optimize out the "down/up" of the device, which needs
>to be done if we allocated a new TX ring.
>
>It also adjusts the semantics of the error return,  in that if the
>TX ring re-sizing went OK but the RX resizing failed, it returns
>success.
>
>That's kind of crummy semantics, if any part fails we should unwind
>and return an error.  So just do the necessary memory allocations
>first, and don't make any changes unless they all succeed.
>
>This code also seems to be incredibly racy.  It allocates the new RING
>structure, and copies the existing entries over.  Meanwhile the chip
>is still running and we're potentially processing these same ring
>entries, so by the time we actually assign adapter->{rx,tx}_ring
>pointers the contents could have changed.
>
>Probably the simplest thing to do is to structure this such that the
>chip is quiesced around the entire ring set operation, so something
>like:

[snip]

I'll take this up and see what I can do to fix it up a bit and address your concerns.  Thanks for the suggestions.

- Greg

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