[PATCH] dmaengine: coh901318: Fix a double lock bug in dma_tc_handle()

[PATCH] dmaengine: coh901318: Fix a double lock bug in dma_tc_handle()

[Dan Carpenter]

The caller is already holding the lock so this will deadlock.

Fixes: 0b58828c923e ("DMAENGINE: COH 901 318 remove irq counting")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
This is the second double lock bug found using static analysis.  The
previous one was commit 627469e4445b ("dmaengine: coh901318: Fix a
double-lock bug").

The fact that this has been broken for ten years suggests that no one
has the hardware.

 drivers/dma/coh901318.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/drivers/dma/coh901318.c b/drivers/dma/coh901318.c
index e51d836afcc7..1092d4ce723e 100644
--- a/drivers/dma/coh901318.c
+++ b/drivers/dma/coh901318.c
@@ -1947,8 +1947,6 @@ static void dma_tc_handle(struct coh901318_chan *cohc)
 		return;
 	}
 
-	spin_lock(&cohc->lock);
-
 	/*
 	 * When we reach this point, at least one queue item
 	 * should have been moved over from cohc->queue to
@@ -1969,8 +1967,6 @@ static void dma_tc_handle(struct coh901318_chan *cohc)
 	if (coh901318_queue_start(cohc) == NULL)
 		cohc->busy = 0;
 
-	spin_unlock(&cohc->lock);
-
 	/*
 	 * This tasklet will remove items from cohc->active
 	 * and thus terminates them.
-- 
2.11.0


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Re: [PATCH] dmaengine: coh901318: Fix a double lock bug in dma_tc_handle()

[Geert Uytterhoeven]

Hi Dan,

On Mon, Feb 17, 2020 at 3:41 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> The caller is already holding the lock so this will deadlock.
>
> Fixes: 0b58828c923e ("DMAENGINE: COH 901 318 remove irq counting")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> This is the second double lock bug found using static analysis.  The
> previous one was commit 627469e4445b ("dmaengine: coh901318: Fix a
> double-lock bug").
>
> The fact that this has been broken for ten years suggests that no one
> has the hardware.

Or this only runs CONFIG_SMP=n kernels?
This seems to be used in arch/arm/boot/dts/ste-u300.dts only, and
CONFIG_ARCH_U300 is a ARCH_MULTI_V5 platform, which looks like
it doesn't support SMP?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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Re: [PATCH] dmaengine: coh901318: Fix a double lock bug in dma_tc_handle()

[Vinod Koul]

On 17-02-20, 23:24, Geert Uytterhoeven wrote:
> Hi Dan,
> 
> On Mon, Feb 17, 2020 at 3:41 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> > The caller is already holding the lock so this will deadlock.
> >
> > Fixes: 0b58828c923e ("DMAENGINE: COH 901 318 remove irq counting")
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > ---
> > This is the second double lock bug found using static analysis.  The
> > previous one was commit 627469e4445b ("dmaengine: coh901318: Fix a
> > double-lock bug").
> >
> > The fact that this has been broken for ten years suggests that no one
> > has the hardware.
> 
> Or this only runs CONFIG_SMP=n kernels?
> This seems to be used in arch/arm/boot/dts/ste-u300.dts only, and
> CONFIG_ARCH_U300 is a ARCH_MULTI_V5 platform, which looks like
> it doesn't support SMP?

Should we drop the driver then..?

-- 
~Vinod

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Re: [PATCH] dmaengine: coh901318: Fix a double lock bug in dma_tc_handle()

[Geert Uytterhoeven]

Hi Vinod,

On Wed, Feb 19, 2020 at 10:18 AM Vinod Koul <vkoul@kernel.org> wrote:
> On 17-02-20, 23:24, Geert Uytterhoeven wrote:
> > On Mon, Feb 17, 2020 at 3:41 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> > > The caller is already holding the lock so this will deadlock.
> > >
> > > Fixes: 0b58828c923e ("DMAENGINE: COH 901 318 remove irq counting")
> > > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > > ---
> > > This is the second double lock bug found using static analysis.  The
> > > previous one was commit 627469e4445b ("dmaengine: coh901318: Fix a
> > > double-lock bug").
> > >
> > > The fact that this has been broken for ten years suggests that no one
> > > has the hardware.
> >
> > Or this only runs CONFIG_SMP=n kernels?
> > This seems to be used in arch/arm/boot/dts/ste-u300.dts only, and
> > CONFIG_ARCH_U300 is a ARCH_MULTI_V5 platform, which looks like
> > it doesn't support SMP?
>
> Should we drop the driver then..?

Why? Because spinlocks are no-ops on SMP=n, and spinlock bugs thus don't
affect the single platform using the driver?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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Re: [PATCH] dmaengine: coh901318: Fix a double lock bug in dma_tc_handle()

[Vinod Koul]

On 19-02-20, 10:20, Geert Uytterhoeven wrote:
> Hi Vinod,
> 
> On Wed, Feb 19, 2020 at 10:18 AM Vinod Koul <vkoul@kernel.org> wrote:
> > On 17-02-20, 23:24, Geert Uytterhoeven wrote:
> > > On Mon, Feb 17, 2020 at 3:41 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> > > > The caller is already holding the lock so this will deadlock.
> > > >
> > > > Fixes: 0b58828c923e ("DMAENGINE: COH 901 318 remove irq counting")
> > > > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > > > ---
> > > > This is the second double lock bug found using static analysis.  The
> > > > previous one was commit 627469e4445b ("dmaengine: coh901318: Fix a
> > > > double-lock bug").
> > > >
> > > > The fact that this has been broken for ten years suggests that no one
> > > > has the hardware.
> > >
> > > Or this only runs CONFIG_SMP=n kernels?
> > > This seems to be used in arch/arm/boot/dts/ste-u300.dts only, and
> > > CONFIG_ARCH_U300 is a ARCH_MULTI_V5 platform, which looks like
> > > it doesn't support SMP?
> >
> > Should we drop the driver then..?
> 
> Why? Because spinlocks are no-ops on SMP=n, and spinlock bugs thus don't
> affect the single platform using the driver?

That doesn't answer the question if anyone has a hardware and we have
users :)

Sorry I should have written better about hardware and testing
rather than cryptic reply which may have suggested about SMP :)

-- 
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Re: [PATCH] dmaengine: coh901318: Fix a double lock bug in dma_tc_handle()

[Linus Walleij]

On Wed, Feb 19, 2020 at 10:17 AM Vinod Koul <vkoul@kernel.org> wrote:
> On 17-02-20, 23:24, Geert Uytterhoeven wrote:
> > On Mon, Feb 17, 2020 at 3:41 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> > > The caller is already holding the lock so this will deadlock.
> > >
> > > Fixes: 0b58828c923e ("DMAENGINE: COH 901 318 remove irq counting")
> > > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > > ---
> > > This is the second double lock bug found using static analysis.  The
> > > previous one was commit 627469e4445b ("dmaengine: coh901318: Fix a
> > > double-lock bug").
> > >
> > > The fact that this has been broken for ten years suggests that no one
> > > has the hardware.
> >
> > Or this only runs CONFIG_SMP=n kernels?
> > This seems to be used in arch/arm/boot/dts/ste-u300.dts only, and
> > CONFIG_ARCH_U300 is a ARCH_MULTI_V5 platform, which looks like
> > it doesn't support SMP?
>
> Should we drop the driver then..?

I still have the hardware and it still works if that is the question :D

And yeah it only has one CPU, but still has a DMA engine.

The patch is fine to apply because it fixes a bug, should the same
hardware block be used on SMP.

Yours,
Linus Walleij

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Re: [PATCH] dmaengine: coh901318: Fix a double lock bug in dma_tc_handle()

[Vinod Koul]

On 21-02-20, 15:50, Linus Walleij wrote:
> On Wed, Feb 19, 2020 at 10:17 AM Vinod Koul <vkoul@kernel.org> wrote:
> > On 17-02-20, 23:24, Geert Uytterhoeven wrote:
> > > On Mon, Feb 17, 2020 at 3:41 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> > > > The caller is already holding the lock so this will deadlock.
> > > >
> > > > Fixes: 0b58828c923e ("DMAENGINE: COH 901 318 remove irq counting")
> > > > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > > > ---
> > > > This is the second double lock bug found using static analysis.  The
> > > > previous one was commit 627469e4445b ("dmaengine: coh901318: Fix a
> > > > double-lock bug").
> > > >
> > > > The fact that this has been broken for ten years suggests that no one
> > > > has the hardware.
> > >
> > > Or this only runs CONFIG_SMP=n kernels?
> > > This seems to be used in arch/arm/boot/dts/ste-u300.dts only, and
> > > CONFIG_ARCH_U300 is a ARCH_MULTI_V5 platform, which looks like
> > > it doesn't support SMP?
> >
> > Should we drop the driver then..?
> 
> I still have the hardware and it still works if that is the question :D

Thanks for confirming :)
> 
> And yeah it only has one CPU, but still has a DMA engine.
> 
> The patch is fine to apply because it fixes a bug, should the same
> hardware block be used on SMP.

Applied now.

-- 
~Vinod

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