From 4548d9f5f9d9816c55422d5c9e7d2eed40668c5f Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Google)" Date: Tue, 27 Sep 2022 14:43:17 -0400 Subject: [PATCH] ring-buffer: Allow splice to read previous partially read pages commit fa8f4a89736b654125fb254b0db753ac68a5fced upstream. If a page is partially read, and then the splice system call is run against the ring buffer, it will always fail to read, no matter how much is in the ring buffer. That's because the code path for a partial read of the page does will fail if the "full" flag is set. The splice system call wants full pages, so if the read of the ring buffer is not yet full, it should return zero, and the splice will block. But if a previous read was done, where the beginning has been consumed, it should still be given to the splice caller if the rest of the page has been written to. This caused the splice command to never consume data in this scenario, and let the ring buffer just fill up and lose events. Link: https://lkml.kernel.org/r/20220927144317.46be6b80@gandalf.local.home Cc: stable@vger.kernel.org Fixes: 8789a9e7df6bf ("ring-buffer: read page interface") Signed-off-by: Steven Rostedt (Google) Signed-off-by: Greg Kroah-Hartman --- kernel/trace/ring_buffer.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index c30a70ab0e7a..4600b6fa2cf4 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -4623,7 +4623,15 @@ int ring_buffer_read_page(struct ring_buffer *buffer, unsigned int pos = 0; unsigned int size; - if (full) + /* + * If a full page is expected, this can still be returned + * if there's been a previous partial read and the + * rest of the page can be read and the commit page is off + * the reader page. + */ + if (full && + (!read || (len < (commit - read)) || + cpu_buffer->reader_page == cpu_buffer->commit_page)) goto out_unlock; if (len > (commit - read))