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From:   Hamza Mahfooz <someguy@effective-light.com>
To:     linux-kernel@vger.kernel.org
Cc:     Hamza Mahfooz <someguy@effective-light.com>,
        Jeremy Linton <jeremy.linton@arm.com>,
        Christoph Hellwig <hch@lst.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>,
        iommu@lists.linux-foundation.org
Subject: [PATCH] dma-debug: prevent an error message from causing runtime problems
Date:   Fri, 10 Sep 2021 08:05:41 -0400
Message-Id: <20210910120541.39938-1-someguy@effective-light.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

For some drivers, that call add_dma_entry() from somewhere down the call
stack. If this error condition is triggered once, it causes the error
message to spam the kernel's printk buffer and bring the CPU usage up to
100%. Also, since there is at least one driver that is in the mainline
and suffers from the error condition, it is more useful to WARN_ON() here
instead of just printing the error message (in hopes that it will make it
easier for other drivers that suffer from this issue to be spotted).

Link: https://lkml.kernel.org/r/fd67fbac-64bf-f0ea-01e1-5938ccfab9d0@arm.com
Reported-by: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: Hamza Mahfooz <someguy@effective-light.com>
---
 kernel/dma/debug.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
index 6c90c69e5311..d9806689666e 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -567,7 +567,9 @@ static void add_dma_entry(struct dma_debug_entry *entry)
 		pr_err("cacheline tracking ENOMEM, dma-debug disabled\n");
 		global_disable = true;
 	} else if (rc == -EEXIST) {
-		pr_err("cacheline tracking EEXIST, overlapping mappings aren't supported\n");
+		WARN_ONCE(1,
+			  pr_fmt("cacheline tracking EEXIST, overlapping mappings aren't supported\n"
+			 ));
 	}
 }
 
-- 
2.33.0