Clarify the check to make sure the number of bytes to allocate is
available.
Reword the comment about the need for the smp_rmb().
Signed-off-by: H Hartley Sweeten <hsweeten@xxxxxxxxxxxxxxxxxxx>
Cc: Ian Abbott <abbobbi@xxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/staging/comedi/comedi_buf.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/drivers/staging/comedi/comedi_buf.c b/drivers/staging/comedi/comedi_buf.c
index 06dd544..971f739 100644
--- a/drivers/staging/comedi/comedi_buf.c
+++ b/drivers/staging/comedi/comedi_buf.c
@@ -291,14 +291,20 @@ EXPORT_SYMBOL(comedi_buf_read_n_available);
/* allocates a chunk for the reader from filled (and munged) buffer space */
unsigned comedi_buf_read_alloc(struct comedi_async *async, unsigned nbytes)
{
- if ((int)(async->buf_read_alloc_count + nbytes - async->munge_count) >
- 0) {
- nbytes = async->munge_count - async->buf_read_alloc_count;
- }
+ unsigned int available;
+
+ available = async->munge_count - async->buf_read_alloc_count;
+ if (nbytes > available)
+ nbytes = available;
+
async->buf_read_alloc_count += nbytes;
- /* barrier insures read of munge_count occurs before we actually read
- data out of buffer */
+
+ /*
+ * ensure the async buffer 'counts' are read before we
+ * attempt to read data from the read-alloc'ed buffer space
+ */
smp_rmb();
+
return nbytes;
}
EXPORT_SYMBOL(comedi_buf_read_alloc);
--
1.8.0
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