dmaengine: pl330: fix the race condition in pl330 driver.

Commit Message

Jassi Brar March 31, 2015, 5:20 a.m. UTC

On Tue, Mar 31, 2015 at 9:10 AM, Scott Branden <[e-mail]> wrote:
> Hi Vinod, Jassi,
>
> Some details on the problem encountered.
>
>
> On 15-03-30 10:25 AM, Vinod Koul wrote:
>>
>> On Mon, Mar 30, 2015 at 10:17:17PM +0530, Jassi Brar wrote:
>>>
>>> On Fri, Mar 27, 2015 at 5:25 AM, Scott Branden <[e-mail]>
>>> wrote:
>>>>
>>>> From: ismail <[e-mail]>
>>>>
>>>> Update the thread running index before issuing the
>>>> GO command to the DMAC.
>>>>
>>>> Tested-by: Mohamed Ismail Abdul Packir Mohamed <[e-mail]>
>>>> Reviewed-by: Ray Jui <[e-mail]>
>>>> Reviewed-by: Arun Parameswaran <[e-mail]>
>>>> Reviewed-by: Scott Branden <[e-mail]>
>>>> Signed-off-by: Scott Branden <[e-mail]>
>>>> Signed-off-by: Mohamed Ismail Abdul Packir Mohamed <[e-mail]>
>>>> ---
>>>>   drivers/dma/pl330.c | 4 ++--
>>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
>>>> index 0e1f567..631642d 100644
>>>> --- a/drivers/dma/pl330.c
>>>> +++ b/drivers/dma/pl330.c
>>>> @@ -1072,11 +1072,11 @@ static bool _trigger(struct pl330_thread *thrd)
>>>>          /* Set to generate interrupts for SEV */
>>>>          writel(readl(regs + INTEN) | (1 << thrd->ev), regs + INTEN);
>>>>
>>>> +       thrd->req_running = idx;
>>>> +
>>>>          /* Only manager can execute GO */
>>>>          _execute_DBGINSN(thrd, insn, true);
>>>>
>>>> -       thrd->req_running = idx;
>>>> -
>>>
>>> It would help to know what the behavior looks like before and after
>>> the patch. If anything we should look at locking rather the
>>> reordering.
>>
>> Yes that ia fair request, looking at changelog it is hard to understand
>> the
>> issue seen?
>>
> We encountered this problem as we modified the driver to make SMC calls to a
> TZ handler.  This slowed down the driver to the point where DMA transactions
> easily failed.  I believe the same could be accomplished by adding a delay
> between the GOCMD and update of the req_running and running the built in
> dmatest.
>
> The DMA transaction is broken if the interrupt occurs before the
> thrd->req_running is updated.
>
> The pl330 issues a GOCMD (in _trigger function) to start a new transfer.
>
> The issue of GOCMD generates an interrupt and the IRQ handler will call the
> pl330_update function to process the interrupt.
>
> The pl330_update function will verify the thread running index and break the
> transaction, if the thread running index is not set.
>
As I suspected the locking seems screwed up. The following patch
should fix the race properly. Can you please test the attached patches
instead?

Thanks.

Patch

From 2cd6bf6748f28008a1650dca57a8f14b27283803 Mon Sep 17 00:00:00 2001
From: Jassi Brar <[e-mail]>
Date: Tue, 31 Mar 2015 10:21:14 +0530
Subject: [PATCH 2/2] dma: pl330: fix race between trigger and completion

We need to hold the lock on channel in ISR to prevent it
racing against the trigger call on the channel.

Reported-by: Scott Branden <[e-mail]>
Signed-off-by: Jassi Brar <[e-mail]>
---
 drivers/dma/pl330.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
index d1f777e..ce40677 100644
--- a/drivers/dma/pl330.c
+++ b/drivers/dma/pl330.c
@@ -1573,6 +1573,7 @@  static int pl330_update(struct pl330_dmac *pl330)
 		if (val & (1 << ev)) { /* Event occurred */
 			struct pl330_thread *thrd;
 			u32 inten = readl(regs + INTEN);
+			unsigned long flag;
 			int active;
 
 			/* Clear the event */
@@ -1584,10 +1585,13 @@  static int pl330_update(struct pl330_dmac *pl330)
 			id = pl330->events[ev];
 
 			thrd = &pl330->channels[id];
+			spin_lock_irqsave(&thrd->pch->lock, flag);
 
 			active = thrd->req_running;
-			if (active == -1) /* Aborted */
+			if (active == -1) { /* Aborted */
+				spin_unlock_irqrestore(&thrd->pch->lock, flag);
 				continue;
+			}
 
 			/* Detach the req */
 			descdone = thrd->req[active].desc;
@@ -1600,6 +1604,7 @@  static int pl330_update(struct pl330_dmac *pl330)
 
 			/* For now, just make a list of callbacks to be done */
 			list_add_tail(&descdone->rqd, &pl330->req_done);
+			spin_unlock_irqrestore(&thrd->pch->lock, flag);
 		}
 	}
 
-- 
1.9.1