On Wed, Dec 28, 2016 at 05:42:13PM -0600, Grygorii Strashko wrote:
Grygorii,
> Now below code sequence causes "Unable to handle kernel NULL pointer
> dereference.." exception and system crash during CPSW CPDMA initialization:
>
> cpsw_probe
> |-cpdma_chan_create (TX channel)
> |-cpdma_chan_split_pool
> |-cpdma_chan_set_descs(for TX channels)
> |-cpdma_chan_set_descs(for RX channels) [1]
>
> - and -
> static void cpdma_chan_set_descs(struct cpdma_ctlr *ctlr,
> int rx, int desc_num,
> int per_ch_desc)
> {
> struct cpdma_chan *chan, *most_chan = NULL;
>
> ...
>
> for (i = min; i < max; i++) {
> chan = ctlr->channels[i];
> if (!chan)
> continue;
> ...
>
> if (most_dnum < chan->desc_num) {
> most_dnum = chan->desc_num;
> most_chan = chan;
> }
> }
> /* use remains */
> most_chan->desc_num += desc_cnt; [2]
> }
>
> So, most_chan value will never be reassigned when cpdma_chan_set_descs() is
> called second time [1], because there are no RX channels yet and system
> will crash at [2].
How did you get this?
I just remember as I fixed it before sending patchset.
Maybe it was some experiment with it.
I just wonder and want to find actual reason what's happening.
Look bellow:
cpsw_probe
|-cpdma_chan_create (TX channel)
|-cpdma_chan_split_pool
|-cpdma_chan_set_descs(for TX channels)
|-cpdma_chan_set_descs(for RX channels) [1]
|-cpdma_chan_set_descs(for RX channels) in case you'be described has to be
called with rx_desc_num = 0, because all descs are assigned already for tx
channel. And, if desc_num = 0, cpdma_chan_set_descs just exits and no issues.
So, could you please explain how you get this, in what circumstances.
>
> Hence, fix the issue by checking most_chan for NULL before accessing it.
>
> Fixes: 0fc6432cc78d ("net: ethernet: ti: davinci_cpdma: add weight function for channels")
> Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
> ---
> drivers/net/ethernet/ti/davinci_cpdma.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/ti/davinci_cpdma.c b/drivers/net/ethernet/ti/davinci_cpdma.c
> index 36518fc..b349d572 100644
> --- a/drivers/net/ethernet/ti/davinci_cpdma.c
> +++ b/drivers/net/ethernet/ti/davinci_cpdma.c
> @@ -708,7 +708,8 @@ static void cpdma_chan_set_descs(struct cpdma_ctlr *ctlr,
> }
> }
> /* use remains */
> - most_chan->desc_num += desc_cnt;
> + if (most_chan)
> + most_chan->desc_num += desc_cnt;
> }
>
> /**
> --
> 2.10.1.dirty
>
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