linux-kernel - Re: BUG kmalloc-16: Object already free

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Date:	Tue, 30 Sep 2008 01:47:39 +0200
From:	Marcel Holtmann <marcel@...tmann.org>
To:	Rabin Vincent <rabin@....in>
Cc:	Justin Mattock <justinmattock@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-bluetooth@...r.kernel.org
Subject: Re: BUG kmalloc-16: Object already free

Hi Rabin,

> > After frying my system, I'm finally up and
> > running. Not sure if this was due to a git-pull
> > (only be a few days since the last pull), or what:
> > when waking from suspend I see this
> > (I know it says tainted in it, so this will be the only noise you'll
> > here from me on this);
> > 
> > [  274.327003] =============================================================================
> > [  274.327528] BUG kmalloc-16: Object already free
> > [  274.327877] -----------------------------------------------------------------------------
> > [  274.327879]
> > [  274.327890] INFO: Allocated in btusb_open+0x82/0x16f [btusb] age=0
> > cpu=1 pid=3763
> > [  274.327899] INFO: Freed in btusb_open+0x13d/0x16f [btusb] age=0
> > cpu=1 pid=3763
> > [  274.327905] INFO: Slab 0xc139a100 objects=64 used=62 fp=0xdcd08100
> > flags=0x400000c3
> 
> There's a commit in the latest git which looks like it will solve the
> btusb suspend/resume issues: 5fbcd260.. ("[Bluetooth] Fix USB disconnect
> handling of btusb driver").
> 
> Marcel / linux-bluetooth, I think this double free is a separate issue
> with the error handling, and the following patch should fix it.
> 
> ---
> From: Rabin Vincent <rabin@....in>
> Subject: [PATCH] btusb, bpa10x: fix double frees on error paths
> 
> Justin Mattock reported this double free in btusb:
> 
>   BUG kmalloc-16: Object already free
>   -----------------------------------------------------------------------------
> 
>   INFO: Allocated in btusb_open+0x82/0x16f [btusb] age=3D0 cpu=3D1 pid=3D3763
>   INFO: Freed in btusb_open+0x13d/0x16f [btusb] age=3D0 cpu=3D1 pid=3D3763
> 
> This occurs because the urb's transfer buffer is being freed separately
> in the error path even though the URB_FREE_BUFFER transfer_flag is set
> on the urb.
> 
> There are similar cases elsewhere in btusb and in bpa10x.  Fix all of
> them by removing the additional kfree()'s.

I haven't verified it yet, but it looks like a good catch. Let me double
check this on my test machine. Weird that we never noticed this before
since I have been using the btusb driver for a very long time now.

Regards

Marcel


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