linux-kernel - [PATCH V2 6/6] ARM CoreSight: ETM: Allocate a trace buffer only when necessary

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Date:	Fri, 24 Jan 2014 11:40:56 -0500
From:	Adrien Vergé <adrienverge@...il.com>
To:	Russell King <linux@....linux.org.uk>
Cc:	Adrien Vergé <adrienverge@...il.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Mathieu Poirier <mathieu.poirier@...aro.org>,
	Christopher Covington <cov@...eaurora.org>,
	Dirk Behme <dirk.behme@...bosch.com>,
	Michel Dagenais <michel.dagenais@...ymtl.ca>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH V2 6/6] ARM CoreSight: ETM: Allocate a trace buffer only when necessary

Some user applications try to retrieve trace data often, there
is no need to call vmalloc() when there is 0 byte to fetch.

Signed-off-by: Adrien Vergé <adrienverge@...il.com>
---
 arch/arm/kernel/etm.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/arm/kernel/etm.c b/arch/arm/kernel/etm.c
index 54b5128..bc97240 100644
--- a/arch/arm/kernel/etm.c
+++ b/arch/arm/kernel/etm.c
@@ -309,7 +309,7 @@ static ssize_t etb_read(struct file *file, char __user *data,
 	long length;
 	struct tracectx *t = file->private_data;
 	u32 first = 0;
-	u32 *buf;
+	u32 *buf = NULL;
 
 	mutex_lock(&t->mutex);
 
@@ -327,12 +327,14 @@ static ssize_t etb_read(struct file *file, char __user *data,
 	etb_writel(t, first, ETBR_READADDR);
 
 	length = min(total * 4, (int)len);
-	buf = vmalloc(length);
+	if (length != 0)
+		buf = vmalloc(length);
 
 	dev_dbg(t->dev, "ETB buffer length: %d\n", total);
 	dev_dbg(t->dev, "ETB status reg: %x\n", etb_readl(t, ETBR_STATUS));
-	for (i = 0; i < length / 4; i++)
-		buf[i] = etb_readl(t, ETBR_READMEM);
+	if (buf)
+		for (i = 0; i < length / 4; i++)
+			buf[i] = etb_readl(t, ETBR_READMEM);
 
 	/* the only way to deassert overflow bit in ETB status is this */
 	etb_writel(t, 1, ETBR_CTRL);
@@ -345,7 +347,8 @@ static ssize_t etb_read(struct file *file, char __user *data,
 	etb_lock(t);
 
 	length -= copy_to_user(data, buf, length);
-	vfree(buf);
+	if (buf)
+		vfree(buf);
 
 out:
 	mutex_unlock(&t->mutex);
-- 
1.8.5.2

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