[PATCH v2 21/30] cxlflash: Fix to prevent workq from accessing freed memory

[PATCH v2 21/30] cxlflash: Fix to prevent workq from accessing freed memory

[Matthew R. Ochs]

The workq can process work in parallel with a remove event, leading
to a condition where the workq handler can access freed memory.

To remedy, the workq should be terminated prior to freeing memory. Move
the termination call earlier in remove and use cancel_work_sync() instead
of flush_work() as there is not a need to process any scheduled work when
shutting down.

Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Signed-off-by: Manoj N. Kumar <manoj@linux.vnet.ibm.com>
---
 drivers/scsi/cxlflash/main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/cxlflash/main.c b/drivers/scsi/cxlflash/main.c
index 1856a73..1625aea 100644
--- a/drivers/scsi/cxlflash/main.c
+++ b/drivers/scsi/cxlflash/main.c
@@ -736,12 +736,12 @@ static void cxlflash_remove(struct pci_dev *pdev)
 		scsi_remove_host(cfg->host);
 		/* Fall through */
 	case INIT_STATE_AFU:
+		cancel_work_sync(&cfg->work_q);
 		term_afu(cfg);
 	case INIT_STATE_PCI:
 		pci_release_regions(cfg->dev);
 		pci_disable_device(pdev);
 	case INIT_STATE_NONE:
-		flush_work(&cfg->work_q);
 		free_mem(cfg);
 		scsi_host_put(cfg->host);
 		break;
-- 
2.1.0

[PATCH v2 21/30] cxlflash: Fix to prevent workq from accessing freed memory

[Matthew R. Ochs]

The workq can process work in parallel with a remove event, leading
to a condition where the workq handler can access freed memory.

To remedy, the workq should be terminated prior to freeing memory. Move
the termination call earlier in remove and use cancel_work_sync() instead
of flush_work() as there is not a need to process any scheduled work when
shutting down.

Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Signed-off-by: Manoj N. Kumar <manoj@linux.vnet.ibm.com>
---
 drivers/scsi/cxlflash/main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/cxlflash/main.c b/drivers/scsi/cxlflash/main.c
index 1856a73..1625aea 100644
--- a/drivers/scsi/cxlflash/main.c
+++ b/drivers/scsi/cxlflash/main.c
@@ -736,12 +736,12 @@ static void cxlflash_remove(struct pci_dev *pdev)
 		scsi_remove_host(cfg->host);
 		/* Fall through */
 	case INIT_STATE_AFU:
+		cancel_work_sync(&cfg->work_q);
 		term_afu(cfg);
 	case INIT_STATE_PCI:
 		pci_release_regions(cfg->dev);
 		pci_disable_device(pdev);
 	case INIT_STATE_NONE:
-		flush_work(&cfg->work_q);
 		free_mem(cfg);
 		scsi_host_put(cfg->host);
 		break;
-- 
2.1.0

Re: [PATCH v2 21/30] cxlflash: Fix to prevent workq from accessing freed memory

[Tomas Henzl]

On 16.9.2015 23:31, Matthew R. Ochs wrote:
> The workq can process work in parallel with a remove event, leading
> to a condition where the workq handler can access freed memory.
>
> To remedy, the workq should be terminated prior to freeing memory. Move
> the termination call earlier in remove and use cancel_work_sync() instead
> of flush_work() as there is not a need to process any scheduled work when
> shutting down.
>
> Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
> Signed-off-by: Manoj N. Kumar <manoj@linux.vnet.ibm.com>
> ---
>  drivers/scsi/cxlflash/main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/cxlflash/main.c b/drivers/scsi/cxlflash/main.c
> index 1856a73..1625aea 100644
> --- a/drivers/scsi/cxlflash/main.c
> +++ b/drivers/scsi/cxlflash/main.c
> @@ -736,12 +736,12 @@ static void cxlflash_remove(struct pci_dev *pdev)
>  		scsi_remove_host(cfg->host);
>  		/* Fall through */
>  	case INIT_STATE_AFU:
> +		cancel_work_sync(&cfg->work_q);
>  		term_afu(cfg);

You disable irqs after a call to cancel_work_sync.
That means a late int could trigger the workqueue again?
Please disable irqs earlier - as described in Documentation/PCI/pci.txt

>  	case INIT_STATE_PCI:
>  		pci_release_regions(cfg->dev);
>  		pci_disable_device(pdev);
>  	case INIT_STATE_NONE:
> -		flush_work(&cfg->work_q);
>  		free_mem(cfg);
>  		scsi_host_put(cfg->host);
>  		break;

Re: [PATCH v2 21/30] cxlflash: Fix to prevent workq from accessing freed memory

[Matthew R. Ochs]

> On Sep 21, 2015, at 7:25 AM, Tomas Henzl <thenzl@redhat.com> wrote:
> On 16.9.2015 23:31, Matthew R. Ochs wrote:
>> The workq can process work in parallel with a remove event, leading
>> to a condition where the workq handler can access freed memory.
>> 
>> To remedy, the workq should be terminated prior to freeing memory. Move
>> the termination call earlier in remove and use cancel_work_sync() instead
>> of flush_work() as there is not a need to process any scheduled work when
>> shutting down.
>> 
>> Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
>> Signed-off-by: Manoj N. Kumar <manoj@linux.vnet.ibm.com>
>> ---
>> drivers/scsi/cxlflash/main.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/scsi/cxlflash/main.c b/drivers/scsi/cxlflash/main.c
>> index 1856a73..1625aea 100644
>> --- a/drivers/scsi/cxlflash/main.c
>> +++ b/drivers/scsi/cxlflash/main.c
>> @@ -736,12 +736,12 @@ static void cxlflash_remove(struct pci_dev *pdev)
>> 		scsi_remove_host(cfg->host);
>> 		/* Fall through */
>> 	case INIT_STATE_AFU:
>> +		cancel_work_sync(&cfg->work_q);
>> 		term_afu(cfg);
> 
> You disable irqs after a call to cancel_work_sync.
> That means a late int could trigger the workqueue again?
> Please disable irqs earlier - as described in Documentation/PCI/pci.txt

I'll change the order here such that the work is cancelled after
term_afu() is called.

-matt