Hello Dan,
On Fri, 28 Oct 2022 20:06:34 +0300 Dan Carpenter dan.carpenter@oracle.com wrote:
On Fri, Oct 28, 2022 at 06:58:47PM +0200, Luca Ceresoli wrote:
Hello Dan,
On Fri, 28 Oct 2022 15:34:39 +0300 Dan Carpenter dan.carpenter@oracle.com wrote:
On Fri, Oct 28, 2022 at 10:19:26AM +0200, luca.ceresoli@bootlin.com wrote:
From: Luca Ceresoli luca.ceresoli@bootlin.com
At probe time this code path is followed:
- tegra_csi_init
- tegra_csi_channels_alloc
- for_each_child_of_node(node, channel) -- iterates over channels
- automatically gets 'channel'
- tegra_csi_channel_alloc()
- saves into chan->of_node a pointer to the channel OF node
- automatically gets and puts 'channel'
- now the node saved in chan->of_node has refcount 0, can disappear
- tegra_csi_channels_init
- iterates over channels
- tegra_csi_channel_init -- uses chan->of_node
After that, chan->of_node keeps storing the node until the device is removed.
of_node_get() the node and of_node_put() it during teardown to avoid any risk.
Fixes: 1ebaeb09830f ("media: tegra-video: Add support for external sensor capture") Cc: stable@vger.kernel.org Cc: Sowjanya Komatineni skomatineni@nvidia.com Signed-off-by: Luca Ceresoli luca.ceresoli@bootlin.com
drivers/staging/media/tegra-video/csi.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/staging/media/tegra-video/csi.c b/drivers/staging/media/tegra-video/csi.c index b26e44adb2be..1b05f620b476 100644 --- a/drivers/staging/media/tegra-video/csi.c +++ b/drivers/staging/media/tegra-video/csi.c @@ -433,7 +433,7 @@ static int tegra_csi_channel_alloc(struct tegra_csi *csi, for (i = 0; i < chan->numgangports; i++) chan->csi_port_nums[i] = port_num + i * CSI_PORTS_PER_BRICK;
- chan->of_node = node;
- chan->of_node = of_node_get(node); chan->numpads = num_pads; if (num_pads & 0x2) { chan->pads[0].flags = MEDIA_PAD_FL_SINK;
@@ -640,6 +640,7 @@ static void tegra_csi_channels_cleanup(struct tegra_csi *csi) media_entity_cleanup(&subdev->entity); }
of_node_put(chan->of_node);Not related to your patch, but this kind of "one function cleans up everything" style is always buggy. For example, here it should be:
if (chan->mipi)
if (!IS_ERR_OR_NULL(chan->mipi)) tegra_mipi_free(chan->mipi);I sort of agree the code could be clearer here, but looking at the code in detail, this cannot happen. chan->mipi is set in one place only, and if it is an error the whole probe fails. So it can be either NULL or a valid pointer here.
I assumed that tegra_csi_channels_cleanup() would clean up if tegra_csi_channel_alloc() fails. Otherwise then that's several different even worse bugs.
HINT: Let's all hope my initial analysis was correct.
Indeed you have a point. Apologies for having replied in a hurry and for the resulting noise.
I'm going to send a patch to fix the chan->mipi mess. However I think the best way to do so would be a oneliner:
@@ -491,6 +491,7 @@ static int tegra_csi_channel_alloc(struct tegra_csi *csi, chan->mipi = tegra_mipi_request(csi->dev, node); if (IS_ERR(chan->mipi)) { ret = PTR_ERR(chan->mipi); + chan->mipi = NULL; dev_err(csi->dev, "failed to get mipi device: %d\n", ret); }
This would be a correct implementation of the initial intent as it can be inferred from the code, i.e. chan->mipi being either NULL or a valid pointer. This makes sense as chan->mipi is assigned in a single place.