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

[Christophe JAILLET]

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_tx_status()
> >      -> 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>
>
> Logan

Hi,

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

CJ

[1]: 
https://lore.kernel.org/all/5125e39b-0faf-63fc-0c51-982b2a567e21@xxxxxxxxxx/