linux-kernel - Re: [PATCH] et131x: fix allocation failures

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Message-ID: <8738jefpta.fsf@will.lan>
Date:	Thu, 20 Feb 2014 11:03:45 +0800
From:	"Zhao\, Gang" <gamerh2o@...il.com>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:	devel@...verdev.osuosl.org, mark.einon@...il.com,
	linux-kernel@...r.kernel.org, greg@...ah.com
Subject: Re: [PATCH] et131x: fix allocation failures

On Wed, 2014-02-19 at 19:43:15 +0800, One Thousand Gnomes wrote:
> On Wed, 19 Feb 2014 09:14:19 +0800
> "Zhao\, Gang" <gamerh2o@...il.com> wrote:
>
>> Alan, thanks for resending this patch. But it seems you overlooked
>> something we discussed earlier.
>> 
>> On Mon, 2014-02-17 at 22:13:08 +0800, Alan wrote:
>> > We should check the ring allocations don't fail.
>> > If we get a fail we need to clean up properly. The allocator assumes the
>> > deallocator will be used on failure, but it isn't. Make sure the
>> > right deallocator is always called and add a missing check against
>> > fbr allocation failure.
>> >
>> > [v2]: Correct check logic
>> >
>> > Signed-off-by: Alan Cox <alan@...ux.intel.com>
>> > ---
>> >  drivers/staging/et131x/et131x.c |    9 +++++++--
>> >  1 file changed, 7 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/drivers/staging/et131x/et131x.c b/drivers/staging/et131x/et131x.c
>> > index 6413500..cc600df 100644
>> > --- a/drivers/staging/et131x/et131x.c
>> > +++ b/drivers/staging/et131x/et131x.c
>> > @@ -2124,7 +2124,11 @@ static int et131x_rx_dma_memory_alloc(struct et131x_adapter *adapter)
>> >  
>> >  	/* Alloc memory for the lookup table */
>> >  	rx_ring->fbr[0] = kmalloc(sizeof(struct fbr_lookup), GFP_KERNEL);
>> > +	if (rx_ring->fbr[0] == NULL)
>> > +		return -ENOMEM;
>> >  	rx_ring->fbr[1] = kmalloc(sizeof(struct fbr_lookup), GFP_KERNEL);
>> > +	if (rx_ring->fbr[1] == NULL)
>> > +		return -ENOMEM;
>> 
>> Shouldn't rx_ring->fbr[0] be freed when allocation of rx_ring->fbr[1]
>> fails ? Or we will leak memory here.
>
> No.. the tx_dma_memory_free and rx_dma_memory_free functions are
> designed to handle incomplete set up. They are now called on incomplete
> setup and will clean up all the resources.
>

Yes, you are right. By calling {tx, rx}_dma_memory_free the memory will
be freed.

But I think a comment is needed here, to make this more clear ? Without
proper comment the above code looks a little strange to let one think
it's right. :)


>> > @@ -3591,6 +3595,7 @@ static int et131x_adapter_memory_alloc(struct et131x_adapter *adapter)
>> >  	if (status) {
>> >  		dev_err(&adapter->pdev->dev,
>> >  			  "et131x_tx_dma_memory_alloc FAILED\n");
>> > +		et131x_tx_dma_memory_free(adapter);
>> >  		return status;
>> >  	}
>> >  	/* Receive buffer memory allocation */
>> > @@ -3598,7 +3603,7 @@ static int et131x_adapter_memory_alloc(struct et131x_adapter *adapter)
>> >  	if (status) {
>> >  		dev_err(&adapter->pdev->dev,
>> >  			  "et131x_rx_dma_memory_alloc FAILED\n");
>> > -		et131x_tx_dma_memory_free(adapter);
>> > +		et131x_adapter_memory_free(adapter);
>> >  		return status;
>> >  	}
>> >  
>
> Which is what these changes are about.
>
> Whoever wrote the allocator and cleanup methods arranged (except for the
> rx_ring->fbr cases) that the free method should be called on a failure.
> It looks as if somewhere along the line of the driver development whoever
> wrote the higher level bits didn't understand that.
>
> Alan
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