RE: [PATCH v7 6/8] fsl-dma: use spin_lock_bh to instead of spin_lock_irqsave

[Liu Qiang-B32616]

 -Original Message-
 From: dan.j.willi...@gmail.com [mailto:dan.j.willi...@gmail.com] On
 Behalf Of Dan Williams
 Sent: Sunday, September 02, 2012 4:41 PM
 To: Liu Qiang-B32616
 Cc: linux-cry...@vger.kernel.org; linuxppc-dev@lists.ozlabs.org; linux-
 ker...@vger.kernel.org; vinod.k...@intel.com; Phillips Kim-R1AAHA;
 herb...@gondor.hengli.com.au; da...@davemloft.net; a...@arndb.de;
 gre...@linuxfoundation.org; Li Yang-R58472; Tabi Timur-B04825
 Subject: Re: [PATCH v7 6/8] fsl-dma: use spin_lock_bh to instead of
 spin_lock_irqsave
 
 On Thu, Aug 9, 2012 at 1:23 AM,  qiang@freescale.com wrote:
  From: Qiang Liu qiang@freescale.com
 
  The use of spin_lock_irqsave() is a stronger locking mechanism than is
  required throughout the driver. The minimum locking required should be
  used instead. Interrupts will be turned off and context will be saved,
  there is needless to use irqsave.
 
  Change all instances of spin_lock_irqsave() to spin_lock_bh().
  All manipulation of protected fields is done using tasklet context or
  weaker, which makes spin_lock_bh() the correct choice.
 
 It seems you are coordinating fsl-dma copy and talitos xor operations.
  It looks like fsl-dma will be called through
 talitos_process_pending()-dma_run_dependencies(), which is
 potentially called in hard irq context.
 
 This all comes back to the need to fix raid offload to manage the
 channels explicitly rather than the current dependency chains.
So you mean I must implement talitos_run_dependencies() and 
fsldma_run_dependencies()? Invoke async_tx-callback() respectively.
How about avoiding irq context in talitos?

 
 --
 Dan


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Re: [PATCH v7 6/8] fsl-dma: use spin_lock_bh to instead of spin_lock_irqsave

[Dan Williams]

On Thu, Aug 9, 2012 at 1:23 AM,  qiang@freescale.com wrote:
 From: Qiang Liu qiang@freescale.com

 The use of spin_lock_irqsave() is a stronger locking mechanism than is
 required throughout the driver. The minimum locking required should be
 used instead. Interrupts will be turned off and context will be saved,
 there is needless to use irqsave.

 Change all instances of spin_lock_irqsave() to spin_lock_bh().
 All manipulation of protected fields is done using tasklet context or
 weaker, which makes spin_lock_bh() the correct choice.

It seems you are coordinating fsl-dma copy and talitos xor operations.
 It looks like fsl-dma will be called through
talitos_process_pending()-dma_run_dependencies(), which is
potentially called in hard irq context.

This all comes back to the need to fix raid offload to manage the
channels explicitly rather than the current dependency chains.

--
Dan
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[PATCH v7 6/8] fsl-dma: use spin_lock_bh to instead of spin_lock_irqsave

[qiang.liu]

From: Qiang Liu qiang@freescale.com

The use of spin_lock_irqsave() is a stronger locking mechanism than is
required throughout the driver. The minimum locking required should be
used instead. Interrupts will be turned off and context will be saved,
there is needless to use irqsave.

Change all instances of spin_lock_irqsave() to spin_lock_bh().
All manipulation of protected fields is done using tasklet context or
weaker, which makes spin_lock_bh() the correct choice.

Cc: Dan Williams dan.j.willi...@intel.com
Cc: Dan Williams dan.j.willi...@gmail.com
Cc: Vinod Koul vinod.k...@intel.com
Cc: Li Yang le...@freescale.com
Cc: Timur Tabi ti...@freescale.com
Signed-off-by: Qiang Liu qiang@freescale.com
Acked-by: Ira W. Snyder i...@ovro.caltech.edu
Acked-by: Arnd Bergmann a...@arndb.de
---
Comments by Arnd Bergmann in v6:
You could actually change the use of spin_lock_bh inside of the tasklet
function (dma_do_tasklet) do just spin_lock(), because softirqs are
already disabled there, but your version is also ok.

 drivers/dma/fsldma.c |   30 --
 1 files changed, 12 insertions(+), 18 deletions(-)

diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c
index b05a81f..8b9c0f7 100644
--- a/drivers/dma/fsldma.c
+++ b/drivers/dma/fsldma.c
@@ -405,10 +405,9 @@ static dma_cookie_t fsl_dma_tx_submit(struct 
dma_async_tx_descriptor *tx)
struct fsldma_chan *chan = to_fsl_chan(tx-chan);
struct fsl_desc_sw *desc = tx_to_fsl_desc(tx);
struct fsl_desc_sw *child;
-   unsigned long flags;
dma_cookie_t cookie;

-   spin_lock_irqsave(chan-desc_lock, flags);
+   spin_lock_bh(chan-desc_lock);

/*
 * assign cookies to all of the software descriptors
@@ -421,7 +420,7 @@ static dma_cookie_t fsl_dma_tx_submit(struct 
dma_async_tx_descriptor *tx)
/* put this transaction onto the tail of the pending queue */
append_ld_queue(chan, desc);

-   spin_unlock_irqrestore(chan-desc_lock, flags);
+   spin_unlock_bh(chan-desc_lock);

return cookie;
 }
@@ -762,15 +761,14 @@ static void fsldma_free_desc_list_reverse(struct 
fsldma_chan *chan,
 static void fsl_dma_free_chan_resources(struct dma_chan *dchan)
 {
struct fsldma_chan *chan = to_fsl_chan(dchan);
-   unsigned long flags;

chan_dbg(chan, free all channel resources\n);
-   spin_lock_irqsave(chan-desc_lock, flags);
+   spin_lock_bh(chan-desc_lock);
fsldma_cleanup_descriptors(chan);
fsldma_free_desc_list(chan, chan-ld_pending);
fsldma_free_desc_list(chan, chan-ld_running);
fsldma_free_desc_list(chan, chan-ld_completed);
-   spin_unlock_irqrestore(chan-desc_lock, flags);
+   spin_unlock_bh(chan-desc_lock);

dma_pool_destroy(chan-desc_pool);
chan-desc_pool = NULL;
@@ -989,7 +987,6 @@ static int fsl_dma_device_control(struct dma_chan *dchan,
 {
struct dma_slave_config *config;
struct fsldma_chan *chan;
-   unsigned long flags;
int size;

if (!dchan)
@@ -999,7 +996,7 @@ static int fsl_dma_device_control(struct dma_chan *dchan,

switch (cmd) {
case DMA_TERMINATE_ALL:
-   spin_lock_irqsave(chan-desc_lock, flags);
+   spin_lock_bh(chan-desc_lock);

/* Halt the DMA engine */
dma_halt(chan);
@@ -1010,7 +1007,7 @@ static int fsl_dma_device_control(struct dma_chan *dchan,
fsldma_free_desc_list(chan, chan-ld_completed);
chan-idle = true;

-   spin_unlock_irqrestore(chan-desc_lock, flags);
+   spin_unlock_bh(chan-desc_lock);
return 0;

case DMA_SLAVE_CONFIG:
@@ -1052,11 +1049,10 @@ static int fsl_dma_device_control(struct dma_chan 
*dchan,
 static void fsl_dma_memcpy_issue_pending(struct dma_chan *dchan)
 {
struct fsldma_chan *chan = to_fsl_chan(dchan);
-   unsigned long flags;

-   spin_lock_irqsave(chan-desc_lock, flags);
+   spin_lock_bh(chan-desc_lock);
fsl_chan_xfer_ld_queue(chan);
-   spin_unlock_irqrestore(chan-desc_lock, flags);
+   spin_unlock_bh(chan-desc_lock);
 }

 /**
@@ -1069,15 +1065,14 @@ static enum dma_status fsl_tx_status(struct dma_chan 
*dchan,
 {
struct fsldma_chan *chan = to_fsl_chan(dchan);
enum dma_status ret;
-   unsigned long flags;

ret = dma_cookie_status(dchan, cookie, txstate);
if (ret == DMA_SUCCESS)
return ret;

-   spin_lock_irqsave(chan-desc_lock, flags);
+   spin_lock_bh(chan-desc_lock);
fsldma_cleanup_descriptors(chan);
-   spin_unlock_irqrestore(chan-desc_lock, flags);
+   spin_unlock_bh(chan-desc_lock);

return dma_cookie_status(dchan, cookie, txstate);
 }
@@ -1156,11 +1151,10 @@ static irqreturn_t fsldma_chan_irq(int irq, void *data)
 static void dma_do_tasklet(unsigned long data)
 {
struct fsldma_chan *chan = (struct fsldma_chan *)data;
-