Re: [PATCH] dmaengine: plx_dma: Fix potential deadlock on &plxdev->ring_lock

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Le 26/07/2023 à 17:57, Logan Gunthorpe a écrit :

On 2023-07-26 04:48, Chengfeng Ye wrote:
As plx_dma_process_desc() is invoked by both tasklet plx_dma_desc_task()
under softirq context and plx_dma_tx_status() callback that executed under
process context, the lock aquicision of &plxdev->ring_lock inside
plx_dma_process_desc() should disable irq otherwise deadlock could happen
if the irq preempts the execution of process context code while the lock
is held in process context on the same CPU.

Possible deadlock scenario:
     -> plx_dma_process_desc()
     -> spin_lock(&plxdev->ring_lock)
         <tasklet softirq>
         -> plx_dma_desc_task()
         -> plx_dma_process_desc()
         -> spin_lock(&plxdev->ring_lock) (deadlock here)

This flaw was found by an experimental static analysis tool I am developing
for irq-related deadlock.

The tentative patch fixes the potential deadlock by spin_lock_irqsave() in
plx_dma_process_desc() to disable irq while lock is held.

Signed-off-by: Chengfeng Ye <dg573847474@xxxxxxxxx>

Makes sense. Thanks!

Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>



as explained in another reply [1], would spin_lock_bh() be enough in such a case?



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