netdev - Re: [PATCH for 3.19] rtlwifi: Fix error when accessing unmapped memory in skb

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Message-ID: <54989E12.6050808@lwfinger.net>
Date:	Mon, 22 Dec 2014 16:41:22 -0600
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Eric Biggers <ebiggers3@...il.com>
CC:	kvalo@...eaurora.org, linux-wireless@...r.kernel.org,
	netdev@...r.kernel.org, Stable <stable@...r.kernel.org>
Subject: Re: [PATCH for 3.19] rtlwifi: Fix error when accessing unmapped memory
 in skb

On 12/22/2014 01:48 PM, Eric Biggers wrote:
> Is this really the same behavior as 3.17?  In 3.17, allocating the new skb is
> one of the first things the interrupt handler does, and if that fails it drops
> the packet and keeps using the old skb.  In this proposal, it's only after the
> packet has been received and the old skb has been freed that a new one is
> allocated.  And if that fails --- well, what are you expecting to happen
> exactly?

You are correct. In trying to get a small patch for stable, I missed some 
important points.

Please look at the attached patch. I think it handles the skb allocations 
correctly. The critical point is that _rtl_pci_init_one_rxdesc() cannot be 
allowed to fail to allocate an skb while in the interrupt path. Now, I have 
already allocated the skb before the call and bypassed this routine if the 
allocation fails. After a couple of crashes, this one now works for the case 
when the allocation wouldn't fail anyway. I will likely pull the allocation out 
of _rtl_pci_init_one_rxdesc() in all cases for the final patch.

@Kalle: Please drop the patch I submitted this morning with this subject. It 
would not help the problem. I will resubmit after I am sure of the proper fix.

Thanks,

Larry

View attachment "fix_skb_alloc_v2" of type "text/plain" (3219 bytes)