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From:   shravan kumar <shravan.chippa@microchip.com>
To:     <green.wan@sifive.com>, <vkoul@kernel.org>, <palmer@dabbelt.com>,
        <paul.walmsley@sifive.com>
CC:     <linux-kernel@vger.kernel.org>, <linux-riscv@lists.infradead.org>,
        <dmaengine@vger.kernel.org>, <shravan.chippa@microchip.com>
Subject: [PATCH v1] dmaengine: sf-pdma: pdma_desc memory leak fix
Date:   Fri, 20 Jan 2023 15:36:23 +0530
Message-ID: <20230120100623.3530634-1-shravan.chippa@microchip.com>
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From: Shravan Chippa <shravan.chippa@microchip.com>

Commit b2cc5c465c2c ("dmaengine: sf-pdma: Add multithread support for a
DMA channel") changed sf_pdma_prep_dma_memcpy() to unconditionally
allocate a new sf_pdma_desc each time it is called.

The driver previously recycled descs, by checking the in_use flag, only
allocating additional descs if the existing one was in use. This logic
was removed in commit b2cc5c465c2c ("dmaengine: sf-pdma: Add multithread
support for a DMA channel"), but sf_pdma_free_desc() was not changed to
handle the new behaviour.

As a result, each time sf_pdma_prep_dma_memcpy() is called, the previous
descriptor is leaked, over time leading to memory starvation:

  unreferenced object 0xffffffe008447300 (size 192):
  comm "irq/39-mchp_dsc", pid 343, jiffies 4294906910 (age 981.200s)
  hex dump (first 32 bytes):
    00 00 00 ff 00 00 00 00 b8 c1 00 00 00 00 00 00  ................
    00 00 70 08 10 00 00 00 00 00 00 c0 00 00 00 00  ..p.............
  backtrace:
    [<00000000064a04f4>] kmemleak_alloc+0x1e/0x28
    [<00000000018927a7>] kmem_cache_alloc+0x11e/0x178
    [<000000002aea8d16>] sf_pdma_prep_dma_memcpy+0x40/0x112

Add the missing kfree() to sf_pdma_free_desc(), and remove the redundant
in_use flag.

Fixes: b2cc5c465c2c ("dmaengine: sf-pdma: Add multithread support for a DMA channel")
Signed-off-by: Shravan Chippa <shravan.chippa@microchip.com>
---
 drivers/dma/sf-pdma/sf-pdma.c | 3 +--
 drivers/dma/sf-pdma/sf-pdma.h | 1 -
 2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/dma/sf-pdma/sf-pdma.c b/drivers/dma/sf-pdma/sf-pdma.c
index 6b524eb6bcf3..e578ad556949 100644
--- a/drivers/dma/sf-pdma/sf-pdma.c
+++ b/drivers/dma/sf-pdma/sf-pdma.c
@@ -96,7 +96,6 @@ sf_pdma_prep_dma_memcpy(struct dma_chan *dchan,	dma_addr_t dest, dma_addr_t src,
 	if (!desc)
 		return NULL;
 
-	desc->in_use = true;
 	desc->dirn = DMA_MEM_TO_MEM;
 	desc->async_tx = vchan_tx_prep(&chan->vchan, &desc->vdesc, flags);
 
@@ -290,7 +289,7 @@ static void sf_pdma_free_desc(struct virt_dma_desc *vdesc)
 	struct sf_pdma_desc *desc;
 
 	desc = to_sf_pdma_desc(vdesc);
-	desc->in_use = false;
+	kfree(desc);
 }
 
 static void sf_pdma_donebh_tasklet(struct tasklet_struct *t)
diff --git a/drivers/dma/sf-pdma/sf-pdma.h b/drivers/dma/sf-pdma/sf-pdma.h
index dcb3687bd5da..5c398a83b491 100644
--- a/drivers/dma/sf-pdma/sf-pdma.h
+++ b/drivers/dma/sf-pdma/sf-pdma.h
@@ -78,7 +78,6 @@ struct sf_pdma_desc {
 	u64				src_addr;
 	struct virt_dma_desc		vdesc;
 	struct sf_pdma_chan		*chan;
-	bool				in_use;
 	enum dma_transfer_direction	dirn;
 	struct dma_async_tx_descriptor *async_tx;
 };
-- 
2.34.1