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authorPengcheng Yang <yangpc@wangsu.com>2020-06-04 16:51:30 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-06-04 19:06:26 -0700
commit341a7213e5c1ce274cc0f02270054905800ea660 (patch)
tree24ffb5ee7641515733bd3e36f8dd9631c455b4dd /kernel/relay.c
parent54e200ab40fc14c863bcc80a51e20b7906608fce (diff)
downloadlwn-341a7213e5c1ce274cc0f02270054905800ea660.tar.gz
lwn-341a7213e5c1ce274cc0f02270054905800ea660.zip
kernel/relay.c: fix read_pos error when multiple readers
When reading, read_pos should start with bytes_consumed, not file->f_pos. Because when there is more than one reader, the read_pos corresponding to file->f_pos may have been consumed, which will cause the data that has been consumed to be read and the bytes_consumed update error. Signed-off-by: Pengcheng Yang <yangpc@wangsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jens Axboe <axboe@kernel.dk> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jann Horn <jannh@google.com> Cc: Al Viro <viro@zeniv.linux.org.uk>e Link: http://lkml.kernel.org/r/1579691175-28949-1-git-send-email-yangpc@wangsu.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/relay.c')
-rw-r--r--kernel/relay.c17
1 files changed, 7 insertions, 10 deletions
diff --git a/kernel/relay.c b/kernel/relay.c
index dc82705e1cff..204867220f8a 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -996,14 +996,14 @@ static void relay_file_read_consume(struct rchan_buf *buf,
/*
* relay_file_read_avail - boolean, are there unconsumed bytes available?
*/
-static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
+static int relay_file_read_avail(struct rchan_buf *buf)
{
size_t subbuf_size = buf->chan->subbuf_size;
size_t n_subbufs = buf->chan->n_subbufs;
size_t produced = buf->subbufs_produced;
size_t consumed = buf->subbufs_consumed;
- relay_file_read_consume(buf, read_pos, 0);
+ relay_file_read_consume(buf, 0, 0);
consumed = buf->subbufs_consumed;
@@ -1064,23 +1064,20 @@ static size_t relay_file_read_subbuf_avail(size_t read_pos,
/**
* relay_file_read_start_pos - find the first available byte to read
- * @read_pos: file read position
* @buf: relay channel buffer
*
- * If the @read_pos is in the middle of padding, return the
+ * If the read_pos is in the middle of padding, return the
* position of the first actually available byte, otherwise
* return the original value.
*/
-static size_t relay_file_read_start_pos(size_t read_pos,
- struct rchan_buf *buf)
+static size_t relay_file_read_start_pos(struct rchan_buf *buf)
{
size_t read_subbuf, padding, padding_start, padding_end;
size_t subbuf_size = buf->chan->subbuf_size;
size_t n_subbufs = buf->chan->n_subbufs;
size_t consumed = buf->subbufs_consumed % n_subbufs;
+ size_t read_pos = consumed * subbuf_size + buf->bytes_consumed;
- if (!read_pos)
- read_pos = consumed * subbuf_size + buf->bytes_consumed;
read_subbuf = read_pos / subbuf_size;
padding = buf->padding[read_subbuf];
padding_start = (read_subbuf + 1) * subbuf_size - padding;
@@ -1136,10 +1133,10 @@ static ssize_t relay_file_read(struct file *filp,
do {
void *from;
- if (!relay_file_read_avail(buf, *ppos))
+ if (!relay_file_read_avail(buf))
break;
- read_start = relay_file_read_start_pos(*ppos, buf);
+ read_start = relay_file_read_start_pos(buf);
avail = relay_file_read_subbuf_avail(read_start, buf);
if (!avail)
break;