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Subject[PATCH V2 6/6] ARM CoreSight: ETM: Allocate a trace buffer only when necessary
Date
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@gmail.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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