linux-kernel - [PATCH] tools/perf probe: Print a hint if adding a probe fails

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Date:   Thu, 10 Jun 2021 15:14:42 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     <linux-kernel@...r.kernel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Subject: [PATCH] tools/perf probe: Print a hint if adding a probe fails

Adding a probe can fail in a few scenarios. perf already checks for the
address in the kprobe blacklist. However, the address could still be a
jump label, or have a BUG_ON(). In such cases, it isn't always evident
why adding the probe failed. Add a hint so that the user knows how to
proceed.

Reported-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
---
 tools/perf/builtin-probe.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
index 6b150756677014..ff9f3fdce600dd 100644
--- a/tools/perf/builtin-probe.c
+++ b/tools/perf/builtin-probe.c
@@ -352,8 +352,11 @@ static int perf_add_probe_events(struct perf_probe_event *pevs, int npevs)
 	}
 
 	ret = apply_perf_probe_events(pevs, npevs);
-	if (ret < 0)
+	if (ret < 0) {
+		pr_info("Hint: Check dmesg to understand reason for probe failure.\n"
+			"      Consider probing at the next/previous instruction.\n");
 		goto out_cleanup;
+	}
 
 	for (i = k = 0; i < npevs; i++)
 		k += pevs[i].ntevs;

base-commit: 0808b3d5b7514dc856178dbc509929329bbf301d
-- 
2.31.1