linux-kernel - [PATCH 4.4 18/18] perf/x86: Reset destroy callback on event init failure

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Message-Id: <20211014145206.908742524@linuxfoundation.org>
Date:   Thu, 14 Oct 2021 16:53:50 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Anand K Mistry <amistry@...gle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.4 18/18] perf/x86: Reset destroy callback on event init failure

From: Anand K Mistry <amistry@...gle.com>

[ Upstream commit 02d029a41dc986e2d5a77ecca45803857b346829 ]

perf_init_event tries multiple init callbacks and does not reset the
event state between tries. When x86_pmu_event_init runs, it
unconditionally sets the destroy callback to hw_perf_event_destroy. On
the next init attempt after x86_pmu_event_init, in perf_try_init_event,
if the pmu's capabilities includes PERF_PMU_CAP_NO_EXCLUDE, the destroy
callback will be run. However, if the next init didn't set the destroy
callback, hw_perf_event_destroy will be run (since the callback wasn't
reset).

Looking at other pmu init functions, the common pattern is to only set
the destroy callback on a successful init. Resetting the callback on
failure tries to replicate that pattern.

This was discovered after commit f11dd0d80555 ("perf/x86/amd/ibs: Extend
PERF_PMU_CAP_NO_EXCLUDE to IBS Op") when the second (and only second)
run of the perf tool after a reboot results in 0 samples being
generated. The extra run of hw_perf_event_destroy results in
active_events having an extra decrement on each perf run. The second run
has active_events == 0 and every subsequent run has active_events < 0.
When active_events == 0, the NMI handler will early-out and not record
any samples.

Signed-off-by: Anand K Mistry <amistry@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20210929170405.1.I078b98ee7727f9ae9d6df8262bad7e325e40faf0@changeid
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kernel/cpu/perf_event.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index b983d3dc4e6c..851fbdb99767 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -2001,6 +2001,7 @@ static int x86_pmu_event_init(struct perf_event *event)
 	if (err) {
 		if (event->destroy)
 			event->destroy(event);
+		event->destroy = NULL;
 	}

 	if (ACCESS_ONCE(x86_pmu.attr_rdpmc))
-- 
2.33.0