Messages in this thread | | | Subject | Re: [PATCH v2 1/2] dmaengine: pl330: fix descriptor allocation fail | From | Marek Szyprowski <> | Date | Tue, 17 Oct 2017 13:26:31 +0200 |
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Hi Alexander,
It took me a while to test this patch, I've been busy with other stuff...
On 2017-10-04 13:37, Alexander Kochetkov wrote: > If two concurrent threads call pl330_get_desc() when DMAC descriptor > pool is empty it is possible that allocation for one of threads will fail > with message: > > kernel: dma-pl330 20078000.dma-controller: pl330_get_desc:2469 ALERT! > > Here how that can happen. Thread A calls pl330_get_desc() to get > descriptor. If DMAC descriptor pool is empty pl330_get_desc() allocates > new descriptor on shared pool using add_desc() and then get newly > allocated descriptor using pluck_desc(). At the same time thread B calls > pluck_desc() and take newly allocated descriptor. In that case descriptor > allocation for thread A will fail. > > Using on-stack pool for new descriptor allow avoid the issue described. > The patch modify pl330_get_desc() to use on-stack pool for allocation > new descriptors. > > Signed-off-by: Alexander Kochetkov <al.kochet@gmail.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> --- > drivers/dma/pl330.c | 39 ++++++++++++++++++++------------------- > 1 file changed, 20 insertions(+), 19 deletions(-) > > diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c > index b19ee04..deec4a4 100644 > --- a/drivers/dma/pl330.c > +++ b/drivers/dma/pl330.c > @@ -2390,7 +2390,8 @@ static inline void _init_desc(struct dma_pl330_desc *desc) > } > > /* Returns the number of descriptors added to the DMAC pool */ > -static int add_desc(struct pl330_dmac *pl330, gfp_t flg, int count) > +static int add_desc(struct list_head *pool, spinlock_t *lock, > + gfp_t flg, int count) > { > struct dma_pl330_desc *desc; > unsigned long flags; > @@ -2400,27 +2401,28 @@ static int add_desc(struct pl330_dmac *pl330, gfp_t flg, int count) > if (!desc) > return 0; > > - spin_lock_irqsave(&pl330->pool_lock, flags); > + spin_lock_irqsave(lock, flags); > > for (i = 0; i < count; i++) { > _init_desc(&desc[i]); > - list_add_tail(&desc[i].node, &pl330->desc_pool); > + list_add_tail(&desc[i].node, pool); > } > > - spin_unlock_irqrestore(&pl330->pool_lock, flags); > + spin_unlock_irqrestore(lock, flags); > > return count; > } > > -static struct dma_pl330_desc *pluck_desc(struct pl330_dmac *pl330) > +static struct dma_pl330_desc *pluck_desc(struct list_head *pool, > + spinlock_t *lock) > { > struct dma_pl330_desc *desc = NULL; > unsigned long flags; > > - spin_lock_irqsave(&pl330->pool_lock, flags); > + spin_lock_irqsave(lock, flags); > > - if (!list_empty(&pl330->desc_pool)) { > - desc = list_entry(pl330->desc_pool.next, > + if (!list_empty(pool)) { > + desc = list_entry(pool->next, > struct dma_pl330_desc, node); > > list_del_init(&desc->node); > @@ -2429,7 +2431,7 @@ static struct dma_pl330_desc *pluck_desc(struct pl330_dmac *pl330) > desc->txd.callback = NULL; > } > > - spin_unlock_irqrestore(&pl330->pool_lock, flags); > + spin_unlock_irqrestore(lock, flags); > > return desc; > } > @@ -2441,20 +2443,18 @@ static struct dma_pl330_desc *pl330_get_desc(struct dma_pl330_chan *pch) > struct dma_pl330_desc *desc; > > /* Pluck one desc from the pool of DMAC */ > - desc = pluck_desc(pl330); > + desc = pluck_desc(&pl330->desc_pool, &pl330->pool_lock); > > /* If the DMAC pool is empty, alloc new */ > if (!desc) { > - if (!add_desc(pl330, GFP_ATOMIC, 1)) > - return NULL; > + DEFINE_SPINLOCK(lock); > + LIST_HEAD(pool); > > - /* Try again */ > - desc = pluck_desc(pl330); > - if (!desc) { > - dev_err(pch->dmac->ddma.dev, > - "%s:%d ALERT!\n", __func__, __LINE__); > + if (!add_desc(&pool, &lock, GFP_ATOMIC, 1)) > return NULL; > - } > + > + desc = pluck_desc(&pool, &lock); > + WARN_ON(!desc || !list_empty(&pool)); > } > > /* Initialize the descriptor */ > @@ -2868,7 +2868,8 @@ static int __maybe_unused pl330_resume(struct device *dev) > spin_lock_init(&pl330->pool_lock); > > /* Create a descriptor pool of default size */ > - if (!add_desc(pl330, GFP_KERNEL, NR_DEFAULT_DESC)) > + if (!add_desc(&pl330->desc_pool, &pl330->pool_lock, > + GFP_KERNEL, NR_DEFAULT_DESC)) > dev_warn(&adev->dev, "unable to allocate desc\n"); > > INIT_LIST_HEAD(&pd->channels);
Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
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