From: Jassi Brar <jassisinghbrar@gmail.com>
To: Scott Branden <sbranden@broadcom.com>
Cc: Vinod Koul <vinod.koul@intel.com>,
Dan Williams <dan.j.williams@intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
ismail <ismail@broadcom.com>, Anatol Pomazao <anatol@google.com>,
Dmitry Torokhov <dtor@google.com>,
bcm-kernel-feedback-list@broadcom.com,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] dmaengine: pl330: fix the race condition in pl330 driver.
Date: Tue, 31 Mar 2015 10:50:27 +0530 [thread overview]
Message-ID: <CABb+yY3+cNqQHVxZg62CPxhb+oKEXcU-twAvpyo6DWUK_8m4qQ@mail.gmail.com> (raw)
In-Reply-To: <551A173B.4010704@broadcom.com>
[-- Attachment #1: Type: text/plain, Size: 2703 bytes --]
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.
[-- Attachment #2: 0001-dma-pl330-change-busy-marker-for-threads.patch --]
[-- Type: text/x-patch, Size: 3065 bytes --]
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
[-- Attachment #3: 0002-dma-pl330-fix-race-between-trigger-and-completion.patch --]
[-- Type: text/x-patch, Size: 1612 bytes --]
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
next prev parent reply other threads:[~2015-03-31 5:20 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-26 23:55 [PATCH] dmaengine: pl330: fix the race condition in pl330 driver Scott Branden
2015-03-29 21:55 ` Scott Branden
2015-03-30 16:47 ` Jassi Brar
2015-03-30 17:25 ` Vinod Koul
2015-03-31 3:40 ` Scott Branden
2015-03-31 5:20 ` Jassi Brar [this message]
2015-03-31 22:04 ` Scott Branden
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CABb+yY3+cNqQHVxZg62CPxhb+oKEXcU-twAvpyo6DWUK_8m4qQ@mail.gmail.com \
--to=jassisinghbrar@gmail.com \
--cc=anatol@google.com \
--cc=bcm-kernel-feedback-list@broadcom.com \
--cc=dan.j.williams@intel.com \
--cc=dtor@google.com \
--cc=ismail@broadcom.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=sbranden@broadcom.com \
--cc=vinod.koul@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).