On 26. 06. 20, 20:09, Dave Jiang wrote:
> Check dma device list and channel list for empty before iterate as the
> iteration function assume the list to be not empty. With devices and
> channels now being hot pluggable this is a condition that needs to be
> checked. Otherwise it can cause the iterator to spin forever.
Could you be a little bit more specific how this can spin forever? I.e.
can you attach a stacktrace of such a behaviour?
As in the empty case, "&pos->member" is "head" (look into
list_for_each_entry) and the for loop should loop exactly zero times.
> Fixes: e81274cd6b52 ("dmaengine: add support to dynamic register/unregister of channels")
> Reported-by: Swathi Kovvuri <swathi.kovvuri@xxxxxxxxx>
> Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> Tested-by: Swathi Kovvuri <swathi.kovvuri@xxxxxxxxx>
> ---
>
> Rebased to dmaengine next tree
>
> drivers/dma/dmaengine.c | 119 +++++++++++++++++++++++++++++++++++++----------
> 1 file changed, 94 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 2b06a7a8629d..0d6529eff66f 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -85,6 +85,9 @@ static void dmaengine_dbg_summary_show(struct seq_file *s,
> {
> struct dma_chan *chan;
>
> + if (list_empty(&dma_dev->channels))
> + return;
> +
> list_for_each_entry(chan, &dma_dev->channels, device_node) {
> if (chan->client_count) {
> seq_printf(s, " %-13s| %s", dma_chan_name(chan),
> @@ -104,6 +107,11 @@ static int dmaengine_summary_show(struct seq_file *s, void *data)
> struct dma_device *dma_dev = NULL;
>
> mutex_lock(&dma_list_mutex);
> + if (list_empty(&dma_device_list)) {
> + mutex_unlock(&dma_list_mutex);
> + return 0;
> + }
> +
> list_for_each_entry(dma_dev, &dma_device_list, global_node) {
> seq_printf(s, "dma%d (%s): number of channels: %u\n",
> dma_dev->dev_id, dev_name(dma_dev->dev),
> @@ -324,10 +332,15 @@ static struct dma_chan *min_chan(enum dma_transaction_type cap, int cpu)
> struct dma_chan *min = NULL;
> struct dma_chan *localmin = NULL;
>
> + if (list_empty(&dma_device_list))
> + return NULL;
> +
> list_for_each_entry(device, &dma_device_list, global_node) {
> if (!dma_has_cap(cap, device->cap_mask) ||
> dma_has_cap(DMA_PRIVATE, device->cap_mask))
> continue;
> + if (list_empty(&device->channels))
> + continue;
> list_for_each_entry(chan, &device->channels, device_node) {
> if (!chan->client_count)
> continue;
> @@ -365,6 +378,9 @@ static void dma_channel_rebalance(void)
> int cpu;
> int cap;
>
> + if (list_empty(&dma_device_list))
> + return;
> +
> /* undo the last distribution */
> for_each_dma_cap_mask(cap, dma_cap_mask_all)
> for_each_possible_cpu(cpu)
> @@ -373,6 +389,8 @@ static void dma_channel_rebalance(void)
> list_for_each_entry(device, &dma_device_list, global_node) {
> if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
> continue;
> + if (list_empty(&device->channels))
> + continue;
> list_for_each_entry(chan, &device->channels, device_node)
> chan->table_count = 0;
> }
> @@ -556,6 +574,10 @@ void dma_issue_pending_all(void)
> struct dma_chan *chan;
>
> rcu_read_lock();
> + if (list_empty(&dma_device_list)) {
> + rcu_read_unlock();
> + return;
> + }
> list_for_each_entry_rcu(device, &dma_device_list, global_node) {
> if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
> continue;
> @@ -613,6 +635,10 @@ static struct dma_chan *private_candidate(const dma_cap_mask_t *mask,
> dev_dbg(dev->dev, "%s: wrong capabilities\n", __func__);
> return NULL;
> }
> +
> + if (list_empty(&dev->channels))
> + return NULL;
> +
> /* devices with multiple channels need special handling as we need to
> * ensure that all channels are either private or public.
> */
> @@ -749,6 +775,11 @@ struct dma_chan *__dma_request_channel(const dma_cap_mask_t *mask,
>
> /* Find a channel */
> mutex_lock(&dma_list_mutex);
> + if (list_empty(&dma_device_list)) {
> + mutex_unlock(&dma_list_mutex);
> + return NULL;
> + }
> +
> list_for_each_entry_safe(device, _d, &dma_device_list, global_node) {
> /* Finds a DMA controller with matching device node */
> if (np && device->dev->of_node && np != device->dev->of_node)
> @@ -819,6 +850,11 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
>
> /* Try to find the channel via the DMA filter map(s) */
> mutex_lock(&dma_list_mutex);
> + if (list_empty(&dma_device_list)) {
> + mutex_unlock(&dma_list_mutex);
> + return NULL;
> + }
> +
> list_for_each_entry_safe(d, _d, &dma_device_list, global_node) {
> dma_cap_mask_t mask;
> const struct dma_slave_map *map = dma_filter_match(d, name, dev);
> @@ -942,10 +978,17 @@ void dmaengine_get(void)
> mutex_lock(&dma_list_mutex);
> dmaengine_ref_count++;
>
> + if (list_empty(&dma_device_list)) {
> + mutex_unlock(&dma_list_mutex);
> + return;
> + }
> +
> /* try to grab channels */
> list_for_each_entry_safe(device, _d, &dma_device_list, global_node) {
> if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
> continue;
> + if (list_empty(&device->channels))
> + continue;
> list_for_each_entry(chan, &device->channels, device_node) {
> err = dma_chan_get(chan);
> if (err == -ENODEV) {
> @@ -980,10 +1023,17 @@ void dmaengine_put(void)
> mutex_lock(&dma_list_mutex);
> dmaengine_ref_count--;
> BUG_ON(dmaengine_ref_count < 0);
> + if (list_empty(&dma_device_list)) {
> + mutex_unlock(&dma_list_mutex);
> + return;
> + }
> +
> /* drop channel references */
> list_for_each_entry_safe(device, _d, &dma_device_list, global_node) {
> if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
> continue;
> + if (list_empty(&device->channels))
> + continue;
> list_for_each_entry(chan, &device->channels, device_node)
> dma_chan_put(chan);
> }
> @@ -1132,6 +1182,39 @@ void dma_async_device_channel_unregister(struct dma_device *device,
> }
> EXPORT_SYMBOL_GPL(dma_async_device_channel_unregister);
>
> +static int dma_channel_enumeration(struct dma_device *device)
> +{
> + struct dma_chan *chan;
> + int rc;
> +
> + if (list_empty(&device->channels))
> + return 0;
> +
> + /* represent channels in sysfs. Probably want devs too */
> + list_for_each_entry(chan, &device->channels, device_node) {
> + rc = __dma_async_device_channel_register(device, chan);
> + if (rc < 0)
> + return rc;
> + }
> +
> + /* take references on public channels */
> + if (dmaengine_ref_count && !dma_has_cap(DMA_PRIVATE, device->cap_mask))
> + list_for_each_entry(chan, &device->channels, device_node) {
> + /* if clients are already waiting for channels we need
> + * to take references on their behalf
> + */
> + if (dma_chan_get(chan) == -ENODEV) {
> + /* note we can only get here for the first
> + * channel as the remaining channels are
> + * guaranteed to get a reference
> + */
> + return -ENODEV;
> + }
> + }
> +
> + return 0;
> +}
> +
> /**
> * dma_async_device_register - registers DMA devices found
> * @device: pointer to &struct dma_device
> @@ -1247,33 +1330,15 @@ int dma_async_device_register(struct dma_device *device)
> if (rc != 0)
> return rc;
>
> + mutex_lock(&dma_list_mutex);
> mutex_init(&device->chan_mutex);
> ida_init(&device->chan_ida);
> -
> - /* represent channels in sysfs. Probably want devs too */
> - list_for_each_entry(chan, &device->channels, device_node) {
> - rc = __dma_async_device_channel_register(device, chan);
> - if (rc < 0)
> - goto err_out;
> + rc = dma_channel_enumeration(device);
> + if (rc < 0) {
> + mutex_unlock(&dma_list_mutex);
> + goto err_out;
> }
>
> - mutex_lock(&dma_list_mutex);
> - /* take references on public channels */
> - if (dmaengine_ref_count && !dma_has_cap(DMA_PRIVATE, device->cap_mask))
> - list_for_each_entry(chan, &device->channels, device_node) {
> - /* if clients are already waiting for channels we need
> - * to take references on their behalf
> - */
> - if (dma_chan_get(chan) == -ENODEV) {
> - /* note we can only get here for the first
> - * channel as the remaining channels are
> - * guaranteed to get a reference
> - */
> - rc = -ENODEV;
> - mutex_unlock(&dma_list_mutex);
> - goto err_out;
> - }
> - }
> list_add_tail_rcu(&device->global_node, &dma_device_list);
> if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
> device->privatecnt++; /* Always private */
> @@ -1291,6 +1356,9 @@ int dma_async_device_register(struct dma_device *device)
> return rc;
> }
>
> + if (list_empty(&device->channels))
> + return rc;
> +
> list_for_each_entry(chan, &device->channels, device_node) {
> if (chan->local == NULL)
> continue;
> @@ -1317,8 +1385,9 @@ void dma_async_device_unregister(struct dma_device *device)
>
> dmaengine_debug_unregister(device);
>
> - list_for_each_entry_safe(chan, n, &device->channels, device_node)
> - __dma_async_device_channel_unregister(device, chan);
> + if (!list_empty(&device->channels))
> + list_for_each_entry_safe(chan, n, &device->channels, device_node)
> + __dma_async_device_channel_unregister(device, chan);
>
> mutex_lock(&dma_list_mutex);
> /*
--
js
suse labs
