linux-kernel - [PATCH 06/10] dmapool: ignore init_on_free when DMAPOOL

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Message-ID: <d7499103-95c4-a002-cb6c-c8c5e3375a8d@cybernetics.com>
Date:   Tue, 31 May 2022 14:20:51 -0400
From:   Tony Battersby <tonyb@...ernetics.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     iommu@...ts.linux-foundation.org, kernel-team@...com,
        Matthew Wilcox <willy@...radead.org>,
        Keith Busch <kbusch@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        Tony Lindgren <tony@...mide.com>
Subject: [PATCH 06/10] dmapool: ignore init_on_free when DMAPOOL_DEBUG enabled

There are two cases:

1) In the normal case that the memory is being freed correctly, then
DMAPOOL_DEBUG will memset the memory anyway, so speed things up by
avoiding a double-memset of the same memory.

2) In the abnormal case that DMAPOOL_DEBUG detects that a driver passes
incorrect parameters to dma_pool_free() (e.g. double-free, invalid
free, mismatched vaddr/dma, etc.), then that is a kernel bug, and we
don't want to clear the passed-in possibly-invalid memory pointer
because we can't be sure that the memory is really free.  So don't clear
it just because init_on_free=1.

Signed-off-by: Tony Battersby <tonyb@...ernetics.com>
---
 mm/dmapool.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/dmapool.c b/mm/dmapool.c
index 7a9161d4f7a6..49019ef6dd83 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -415,8 +415,6 @@ void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
 	}
 
 	offset = vaddr - page->vaddr;
-	if (want_init_on_free())
-		memset(vaddr, 0, pool->size);
 #ifdef	DMAPOOL_DEBUG
 	if ((dma - page->dma) != offset) {
 		spin_unlock_irqrestore(&pool->lock, flags);
@@ -461,6 +459,9 @@ void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
 			goto freelist_corrupt;
 	}
 	memset(vaddr, POOL_POISON_FREED, pool->size);
+#else
+	if (want_init_on_free())
+		memset(vaddr, 0, pool->size);
 #endif
 
 	page->in_use--;
-- 
2.25.1