[PATCH] kfifo: roundup fifo size to next power of two

Sascha Hauer s.hauer at pengutronix.de
Fri Sep 21 04:14:05 PDT 2018


Comments in include/kfifo.h state that the FIFO size will be rounded up
to the next power of two, but so far we haven't actually done this,
probably because we didn't have roundup_pow_of_two() back then when
kfifo support was added.

Fix that now and do what the comments state.

Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
---
 lib/kfifo.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/lib/kfifo.c b/lib/kfifo.c
index 307dae1441..fa22feb7e0 100644
--- a/lib/kfifo.c
+++ b/lib/kfifo.c
@@ -18,6 +18,7 @@
 #include <malloc.h>
 #include <kfifo.h>
 #include <errno.h>
+#include <linux/log2.h>
 
 /**
  * kfifo_init - allocates a new FIFO using a preallocated buffer
@@ -49,6 +50,15 @@ struct kfifo *kfifo_alloc(unsigned int size)
 	unsigned char *buffer;
 	struct kfifo *fifo;
 
+	/*
+	 * round up to the next power of 2, since our 'let the indices
+	 * wrap' tachnique works only in this case.
+	 */
+	if (size & (size - 1)) {
+		BUG_ON(size > 0x80000000);
+		size = roundup_pow_of_two(size);
+	}
+
 	buffer = malloc(size);
 	if (!buffer)
 		return NULL;
-- 
2.19.0




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