On driver unload any pending descriptors are flushed and pending
DMA descriptors are explicitly completed:
idxd_dmaengine_drv_remove() ->
drv_disable_wq() ->
idxd_wq_free_irq() ->
idxd_flush_pending_descs() ->
idxd_dma_complete_txd()
With this done during driver unload any remaining descriptor is
likely stuck and can be dropped. Even so, the descriptor may still
have a callback set that could no longer be accessible. An
example of such a problem is when the dmatest fails and the dmatest
module is unloaded. The failure of dmatest leaves descriptors with
dma_async_tx_descriptor::callback pointing to code that no longer
exist. This causes a page fault as below at the time the IDXD driver
is unloaded when it attempts to run the callback:
BUG: unable to handle page fault for address: ffffffffc0665190
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
Fix this by clearing the callback pointers on the transmit
descriptors only when workqueue is disabled.
Signed-off-by: Reinette Chatre <[email protected]>
---
History of refactoring made the Fixes: hard to identify by me.
drivers/dma/idxd/device.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/drivers/dma/idxd/device.c b/drivers/dma/idxd/device.c
index b4d7bb923a40..2ac71a34fa34 100644
--- a/drivers/dma/idxd/device.c
+++ b/drivers/dma/idxd/device.c
@@ -1156,6 +1156,7 @@ int idxd_device_load_config(struct idxd_device *idxd)
static void idxd_flush_pending_descs(struct idxd_irq_entry *ie)
{
+ struct dma_async_tx_descriptor *tx;
struct idxd_desc *desc, *itr;
struct llist_node *head;
LIST_HEAD(flist);
@@ -1175,6 +1176,15 @@ static void idxd_flush_pending_descs(struct idxd_irq_entry *ie)
list_for_each_entry_safe(desc, itr, &flist, list) {
list_del(&desc->list);
ctype = desc->completion->status ? IDXD_COMPLETE_NORMAL : IDXD_COMPLETE_ABORT;
+ /*
+ * wq is being disabled. Any remaining descriptors are
+ * likely to be stuck and can be dropped. callback could
+ * point to code that is no longer accessible, for example
+ * if dmatest module has been unloaded.
+ */
+ tx = &desc->txd;
+ tx->callback = NULL;
+ tx->callback_result = NULL;
idxd_dma_complete_txd(desc, ctype, true);
}
}
--
2.34.1
On 12/2/2022 11:25 AM, Reinette Chatre wrote:
> On driver unload any pending descriptors are flushed and pending
> DMA descriptors are explicitly completed:
> idxd_dmaengine_drv_remove() ->
> drv_disable_wq() ->
> idxd_wq_free_irq() ->
> idxd_flush_pending_descs() ->
> idxd_dma_complete_txd()
>
> With this done during driver unload any remaining descriptor is
> likely stuck and can be dropped. Even so, the descriptor may still
> have a callback set that could no longer be accessible. An
> example of such a problem is when the dmatest fails and the dmatest
> module is unloaded. The failure of dmatest leaves descriptors with
> dma_async_tx_descriptor::callback pointing to code that no longer
> exist. This causes a page fault as below at the time the IDXD driver
> is unloaded when it attempts to run the callback:
> BUG: unable to handle page fault for address: ffffffffc0665190
> #PF: supervisor instruction fetch in kernel mode
> #PF: error_code(0x0010) - not-present page
>
> Fix this by clearing the callback pointers on the transmit
> descriptors only when workqueue is disabled.
>
> Signed-off-by: Reinette Chatre <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
> ---
>
> History of refactoring made the Fixes: hard to identify by me.
>
> drivers/dma/idxd/device.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/drivers/dma/idxd/device.c b/drivers/dma/idxd/device.c
> index b4d7bb923a40..2ac71a34fa34 100644
> --- a/drivers/dma/idxd/device.c
> +++ b/drivers/dma/idxd/device.c
> @@ -1156,6 +1156,7 @@ int idxd_device_load_config(struct idxd_device *idxd)
>
> static void idxd_flush_pending_descs(struct idxd_irq_entry *ie)
> {
> + struct dma_async_tx_descriptor *tx;
> struct idxd_desc *desc, *itr;
> struct llist_node *head;
> LIST_HEAD(flist);
> @@ -1175,6 +1176,15 @@ static void idxd_flush_pending_descs(struct idxd_irq_entry *ie)
> list_for_each_entry_safe(desc, itr, &flist, list) {
> list_del(&desc->list);
> ctype = desc->completion->status ? IDXD_COMPLETE_NORMAL : IDXD_COMPLETE_ABORT;
> + /*
> + * wq is being disabled. Any remaining descriptors are
> + * likely to be stuck and can be dropped. callback could
> + * point to code that is no longer accessible, for example
> + * if dmatest module has been unloaded.
> + */
> + tx = &desc->txd;
> + tx->callback = NULL;
> + tx->callback_result = NULL;
> idxd_dma_complete_txd(desc, ctype, true);
> }
> }
Hi, Reinette,
> On driver unload any pending descriptors are flushed and pending DMA
> descriptors are explicitly completed:
> idxd_dmaengine_drv_remove() ->
> drv_disable_wq() ->
> idxd_wq_free_irq() ->
> idxd_flush_pending_descs() ->
> idxd_dma_complete_txd()
>
> With this done during driver unload any remaining descriptor is likely stuck and
> can be dropped. Even so, the descriptor may still have a callback set that could
> no longer be accessible. An example of such a problem is when the dmatest fails
> and the dmatest module is unloaded. The failure of dmatest leaves descriptors
> with dma_async_tx_descriptor::callback pointing to code that no longer exist.
> This causes a page fault as below at the time the IDXD driver is unloaded when it
> attempts to run the callback:
> BUG: unable to handle page fault for address: ffffffffc0665190
> #PF: supervisor instruction fetch in kernel mode
> #PF: error_code(0x0010) - not-present page
>
> Fix this by clearing the callback pointers on the transmit descriptors only when
> workqueue is disabled.
>
> Signed-off-by: Reinette Chatre <[email protected]>
> ---
>
> History of refactoring made the Fixes: hard to identify by me.
>
> drivers/dma/idxd/device.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/drivers/dma/idxd/device.c b/drivers/dma/idxd/device.c index
> b4d7bb923a40..2ac71a34fa34 100644
> --- a/drivers/dma/idxd/device.c
> +++ b/drivers/dma/idxd/device.c
> @@ -1156,6 +1156,7 @@ int idxd_device_load_config(struct idxd_device *idxd)
>
> static void idxd_flush_pending_descs(struct idxd_irq_entry *ie) {
> + struct dma_async_tx_descriptor *tx;
Nitpicking. It's better to move this line to below:
> struct idxd_desc *desc, *itr;
> struct llist_node *head;
> LIST_HEAD(flist);
> @@ -1175,6 +1176,15 @@ static void idxd_flush_pending_descs(struct
> idxd_irq_entry *ie)
> list_for_each_entry_safe(desc, itr, &flist, list) {
here?
+ struct dma_async_tx_descriptor *tx;
> list_del(&desc->list);
> ctype = desc->completion->status ?
> IDXD_COMPLETE_NORMAL : IDXD_COMPLETE_ABORT;
> + /*
> + * wq is being disabled. Any remaining descriptors are
> + * likely to be stuck and can be dropped. callback could
> + * point to code that is no longer accessible, for example
> + * if dmatest module has been unloaded.
> + */
> + tx = &desc->txd;
> + tx->callback = NULL;
> + tx->callback_result = NULL;
> idxd_dma_complete_txd(desc, ctype, true);
> }
> }
> --
> 2.34.1
Reviewed-by: Fenghua Yu <[email protected]>
Thanks.
-Fenghua
Hi Fenghua,
On 12/2/2022 1:12 PM, Yu, Fenghua wrote:
...
>> diff --git a/drivers/dma/idxd/device.c b/drivers/dma/idxd/device.c index
>> b4d7bb923a40..2ac71a34fa34 100644
>> --- a/drivers/dma/idxd/device.c
>> +++ b/drivers/dma/idxd/device.c
>> @@ -1156,6 +1156,7 @@ int idxd_device_load_config(struct idxd_device *idxd)
>>
>> static void idxd_flush_pending_descs(struct idxd_irq_entry *ie) {
>> + struct dma_async_tx_descriptor *tx;
>
> Nitpicking. It's better to move this line to below:
>
>> struct idxd_desc *desc, *itr;
>> struct llist_node *head;
>> LIST_HEAD(flist);
>> @@ -1175,6 +1176,15 @@ static void idxd_flush_pending_descs(struct
>> idxd_irq_entry *ie)
>> list_for_each_entry_safe(desc, itr, &flist, list) {
>
> here?
> + struct dma_async_tx_descriptor *tx;
>
Will do.
>> list_del(&desc->list);
>> ctype = desc->completion->status ?
>> IDXD_COMPLETE_NORMAL : IDXD_COMPLETE_ABORT;
>> + /*
>> + * wq is being disabled. Any remaining descriptors are
>> + * likely to be stuck and can be dropped. callback could
>> + * point to code that is no longer accessible, for example
>> + * if dmatest module has been unloaded.
>> + */
>> + tx = &desc->txd;
>> + tx->callback = NULL;
>> + tx->callback_result = NULL;
>> idxd_dma_complete_txd(desc, ctype, true);
>> }
>> }
>> --
>> 2.34.1
>
> Reviewed-by: Fenghua Yu <[email protected]>
Thank you very much.
Reinette