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Commit 4f3640f8 authored by Steven Rostedt's avatar Steven Rostedt
Browse files

ring-buffer: fix timestamp in partial ring_buffer_page_read 



If a partial ring_buffer_page_read happens, then some of the
incremental timestamps may be lost. This patch writes the
recent timestamp into the page that is passed back to the caller.

A partial ring_buffer_page_read is where the full page would not
be written back to the user, and instead, just part of the page
is copied to the user. A full page would be a page swap with the
ring buffer and the timestamps would be correct.

Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
parent e543ad76

kernel/trace/ring_buffer.c

+5 −1
Original line number Diff line number Diff line
@@ -2461,6 +2461,7 @@ int ring_buffer_read_page(struct ring_buffer *buffer, 
	unsigned long flags;

	unsigned int commit;

	unsigned int read;

	u64 save_timestamp;

	int ret = -1;



	/*
@@ -2515,6 +2516,9 @@ int ring_buffer_read_page(struct ring_buffer *buffer, 
		if (len < size)

			goto out;



		/* save the current timestamp, since the user will need it */

		save_timestamp = cpu_buffer->read_stamp;



		/* Need to copy one event at a time */

		do {

			memcpy(bpage->data + pos, rpage->data + rpos, size);
@@ -2531,7 +2535,7 @@ int ring_buffer_read_page(struct ring_buffer *buffer, 


		/* update bpage */

		local_set(&bpage->commit, pos);

		bpage->time_stamp = rpage->time_stamp;

		bpage->time_stamp = save_timestamp;



		/* we copied everything to the beginning */

		read = 0;