relay: fix "full buffer with exactly full last subbuffer" accounting problem

In relay's current read implementation, if the buffer is completely full
but hasn't triggered the buffer-full condition (i.e. the last write
didn't cross the subbuffer boundary) and the last subbuffer is exactly
full, the subbuffer accounting code erroneously finds nothing available.
This patch fixes the problem.

Signed-off-by: Tom Zanussi <[email protected]>
Cc: Eduard - Gabriel Munteanu <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrea Righi <[email protected]>
Cc: <[email protected]>		[2.6.25.x, 2.6.26.x]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/kernel/relay.c b/kernel/relay.c
index 04006ef970b818b01d6cb152c5a5997896a06478..8d13a7855c0808858c20fd01d6decebc08c8eeaa 100644 (file)
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -944,6 +944,10 @@ static void relay_file_read_consume(struct rchan_buf *buf,
        size_t n_subbufs = buf->chan->n_subbufs;
        size_t read_subbuf;
 
+       if (buf->subbufs_produced == buf->subbufs_consumed &&
+           buf->offset == buf->bytes_consumed)
+               return;
+
        if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
                relay_subbufs_consumed(buf->chan, buf->cpu, 1);
                buf->bytes_consumed = 0;
@@ -975,6 +979,8 @@ static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
 
        relay_file_read_consume(buf, read_pos, 0);
 
+       consumed = buf->subbufs_consumed;
+
        if (unlikely(buf->offset > subbuf_size)) {
                if (produced == consumed)
                        return 0;
@@ -993,8 +999,12 @@ static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
        if (consumed > produced)
                produced += n_subbufs * subbuf_size;
 
-       if (consumed == produced)
+       if (consumed == produced) {
+               if (buf->offset == subbuf_size &&
+                   buf->subbufs_produced > buf->subbufs_consumed)
+                       return 1;
                return 0;
+       }
 
        return 1;
 }