Messages in this thread Patches in this message | | | Date | Tue, 31 Mar 2015 10:50:27 +0530 | Subject | Re: [PATCH] dmaengine: pl330: fix the race condition in pl330 driver. | From | Jassi Brar <> |
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On Tue, Mar 31, 2015 at 9:10 AM, Scott Branden <sbranden@broadcom.com> 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 <sbranden@broadcom.com> >>> wrote: >>>> >>>> From: ismail <ismail@broadcom.com> >>>> >>>> Update the thread running index before issuing the >>>> GO command to the DMAC. >>>> >>>> Tested-by: Mohamed Ismail Abdul Packir Mohamed <ismail@broadcom.com> >>>> Reviewed-by: Ray Jui <rjui@broadcom.com> >>>> Reviewed-by: Arun Parameswaran <aparames@broadcom.com> >>>> Reviewed-by: Scott Branden <sbranden@broadcom.com> >>>> Signed-off-by: Scott Branden <sbranden@broadcom.com> >>>> Signed-off-by: Mohamed Ismail Abdul Packir Mohamed <ismail@broadcom.com> >>>> --- >>>> 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. From 1c44fc936d05fef3259354da1574c536ed1691c7 Mon Sep 17 00:00:00 2001 From: Jassi Brar <jaswinder.singh@linaro.org> Date: Tue, 31 Mar 2015 10:16:46 +0530 Subject: [PATCH 1/2] dma: pl330: change busy marker for threads
Instead of a boolean flag to mark a thread busy, use the owner of the thread as the marker. For free/available threads, the owner is NULL. This will be useful in finding which channel owns a given thread.
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org> --- drivers/dma/pl330.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-)
diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c index 0e1f567..d1f777e 100644 --- a/drivers/dma/pl330.c +++ b/drivers/dma/pl330.c @@ -369,8 +369,7 @@ struct _pl330_tbd { struct pl330_thread { u8 id; int ev; - /* If the channel is not yet acquired by any client */ - bool free; + struct dma_pl330_chan *pch; /* Parent DMAC */ struct pl330_dmac *dmac; /* Only two at a time */ @@ -1648,7 +1647,8 @@ static bool _chan_ns(const struct pl330_dmac *pl330, int i) /* Upon success, returns IdentityToken for the * allocated channel, NULL otherwise. */ -static struct pl330_thread *pl330_request_channel(struct pl330_dmac *pl330) +static struct pl330_thread *pl330_request_channel(struct pl330_dmac *pl330, + struct dma_pl330_chan *pch) { struct pl330_thread *thrd = NULL; unsigned long flags; @@ -1663,11 +1663,11 @@ static struct pl330_thread *pl330_request_channel(struct pl330_dmac *pl330) for (i = 0; i < chans; i++) { thrd = &pl330->channels[i]; - if ((thrd->free) && (!_manager_ns(thrd) || + if (!thrd->pch && (!_manager_ns(thrd) || _chan_ns(pl330, i))) { thrd->ev = _alloc_event(thrd); if (thrd->ev >= 0) { - thrd->free = false; + thrd->pch = pch; thrd->lstenq = 1; thrd->req[0].desc = NULL; thrd->req[1].desc = NULL; @@ -1699,7 +1699,7 @@ static void pl330_release_channel(struct pl330_thread *thrd) struct pl330_dmac *pl330; unsigned long flags; - if (!thrd || thrd->free) + if (!thrd || !thrd->pch) return; _stop(thrd); @@ -1711,7 +1711,7 @@ static void pl330_release_channel(struct pl330_thread *thrd) spin_lock_irqsave(&pl330->lock, flags); _free_event(thrd, thrd->ev); - thrd->free = true; + thrd->pch = NULL; spin_unlock_irqrestore(&pl330->lock, flags); } @@ -1797,14 +1797,14 @@ static int dmac_alloc_threads(struct pl330_dmac *pl330) thrd->id = i; thrd->dmac = pl330; _reset_thread(thrd); - thrd->free = true; + thrd->pch = NULL; } /* MANAGER is indexed at the end */ thrd = &pl330->channels[chans]; thrd->id = chans; thrd->dmac = pl330; - thrd->free = false; + thrd->pch = NULL; pl330->manager = thrd; return 0; @@ -2082,7 +2082,7 @@ static int pl330_alloc_chan_resources(struct dma_chan *chan) dma_cookie_init(chan); pch->cyclic = false; - pch->thread = pl330_request_channel(pl330); + pch->thread = pl330_request_channel(pl330, pch); if (!pch->thread) { spin_unlock_irqrestore(&pch->lock, flags); return -ENOMEM; -- 1.9.1 From 2cd6bf6748f28008a1650dca57a8f14b27283803 Mon Sep 17 00:00:00 2001 From: Jassi Brar <jaswinder.singh@linaro.org> 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 <sbranden@broadcom.com> Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org> --- 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
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