Re: [PATCH 3/5] perf: Catch and handle out-of-date hist entry maps.

[David Miller <davem@davemloft.net>]

From: David Miller <davem@davemloft.net>
Date: Sun, 25 Mar 2012 16:28:18 -0400 (EDT)

> @@ -253,6 +253,15 @@ static struct hist_entry *add_hist_entry(struct hists *hists,
>  		if (!cmp) {
>  			he->period += period;
>  			++he->nr_events;
> +
> +			/* If the map of an existing hist_entry has
> +			 * become out-of-date due to an exec() or
> +			 * similar, update it.  Otherwise we will
> +			 * mis-adjust symbol addresses when computing
> +			 * the history counter to increment.
> +			 */
> +			if (he->ms.map != entry->ms.map)
> +				he->ms.map = entry->ms.map;
>  			goto out;

This unfortunately has a bug, when we hook up a map to a hist_entry we
must mark it referenced.  Otherwise it can get freed up prematurely.

Here's a new version of this patch:

--------------------
perf: Catch and handle out-of-date hist entry maps.

When a process exec()'s, all the maps are retired, but we keep the
hist entries around which hold references to those outdated maps.

If the same library gets mapped in for which we have hist entries, a
new map will be created.  But when we take a perf entry hit within
that map, we'll find the existing hist entry with the older map.

This causes symbol translations to be done incorrectly.  For example,
the perf entry processing will lookup the correct uptodate map entry
and use that to calculate the symbol and DSO relative address.  But
later when we update the histogram we'll translate the address using
the outdated map file instead leading to conditions such as
out-of-range offsets in symbol__inc_addr_samples() which now has an
assertion for this situation.

Therefore, update the map of the hist_entry dynamically at
lookup/creation time.

Signed-off-by: David S. Miller <davem@davemloft.net>
---
 tools/perf/util/hist.c |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
index 3dc99a9..bf0f259 100644
--- a/tools/perf/util/hist.c
+++ b/tools/perf/util/hist.c
@@ -253,6 +253,18 @@ static struct hist_entry *add_hist_entry(struct hists *hists,
 		if (!cmp) {
 			he->period += period;
 			++he->nr_events;
+
+			/* If the map of an existing hist_entry has
+			 * become out-of-date due to an exec() or
+			 * similar, update it.  Otherwise we will
+			 * mis-adjust symbol addresses when computing
+			 * the history counter to increment.
+			 */
+			if (he->ms.map != entry->ms.map) {
+				he->ms.map = entry->ms.map;
+				if (he->ms.map)
+					he->ms.map->referenced = true;
+			}
 			goto out;
 		}
 
-- 
1.7.9.1