Messages in this thread | | | Date | Fri, 28 Mar 2014 14:33:37 +0800 | From | Hongbo Zhang <> | Subject | Re: [PATCH 6/7] DMA: Freescale: use spin_lock_bh instead of spin_lock_irqsave |
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On 03/26/2014 03:01 PM, Vinod Koul wrote: > On Thu, 2014-01-16 at 13:47 +0800, hongbo.zhang@freescale.com wrote: >> From: Hongbo Zhang <hongbo.zhang@freescale.com> >> >> The usage 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, it is >> unnecessary to use irqsave. >> >> This patch changes 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. >> >> Signed-off-by: Hongbo Zhang <hongbo.zhang@freescale.com> >> Signed-off-by: Qiang Liu <qiang.liu@freescale.com> >> --- >> drivers/dma/fsldma.c | 25 ++++++++++--------------- >> 1 file changed, 10 insertions(+), 15 deletions(-) >> >> diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c >> index bbace54..437794e 100644 >> --- a/drivers/dma/fsldma.c >> +++ b/drivers/dma/fsldma.c >> @@ -396,10 +396,9 @@ 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 = -EINVAL; >> >> - spin_lock_irqsave(&chan->desc_lock, flags); >> + spin_lock_bh(&chan->desc_lock); >> >> /* >> * assign cookies to all of the software descriptors >> @@ -412,7 +411,7 @@ 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; >> } >> @@ -731,15 +730,14 @@ 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; >> @@ -958,7 +956,6 @@ 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) >> @@ -968,7 +965,7 @@ 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); >> @@ -979,7 +976,7 @@ 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: >> @@ -1021,11 +1018,10 @@ 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); >> } >> >> /** >> @@ -1124,11 +1120,10 @@ 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; >> - unsigned long flags; >> >> chan_dbg(chan, "tasklet entry\n"); >> >> - spin_lock_irqsave(&chan->desc_lock, flags); >> + spin_lock_bh(&chan->desc_lock); > okay here is the problem :( > > You moved to _bh variant. So if you grab the lock in rest of the code > and irq gets triggered then here we will be spinning to grab the lock. > So effectively you made right locking solution into deadlock situation!
If the rest code grabs lock by spin_lock_bh(), and if irq raised, the tasklet could not be executed because it has been disabled by the _bh variant function. Right?
>> >> /* the hardware is now idle and ready for more */ >> chan->idle = true; >> @@ -1136,7 +1131,7 @@ static void dma_do_tasklet(unsigned long data) >> /* Run all cleanup for descriptors which have been completed */ >> fsldma_cleanup_descriptors(chan); >> >> - spin_unlock_irqrestore(&chan->desc_lock, flags); >> + spin_unlock_bh(&chan->desc_lock); >> >> chan_dbg(chan, "tasklet exit\n"); >> } >
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