linux-kernel - Re: [Syzkaller & bisect] There is "__perf_event_overflow" WARNING in v6.1-rc5 kernel in guest

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Date:   Wed, 23 Nov 2022 16:06:17 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Pengfei Xu <pengfei.xu@...el.com>
Cc:     peter.zijlstra@...el.com, linux-kernel@...r.kernel.org,
        heng.su@...el.com, Marco Elver <elver@...gle.com>,
        Mark Rutland <mark.rutland@....com>, namhyung@...nel.org
Subject: Re: [Syzkaller & bisect] There is "__perf_event_overflow" WARNING in
 v6.1-rc5 kernel in guest

On Wed, Nov 23, 2022 at 04:05:14PM +0100, Peter Zijlstra wrote:
> @@ -9330,7 +9350,7 @@ static int __perf_event_overflow(struct
>  		}
>  
>  		event->pending_addr = 0;
> -		if (data->sample_flags & PERF_SAMPLE_ADDR)
> +		if (valid_sample && (data->sample_flags & PERF_SAMPLE_ADDR))
>  			event->pending_addr = data->addr;
>  		irq_work_queue(&event->pending_irq);
>  	}

That is the result of this patch; also found in that branch:

---
Subject: perf: Fixup SIGTRAP and sample_flags interaction
From: Peter Zijlstra <peterz@...radead.org>
Date: Mon Nov 21 15:57:44 CET 2022

The perf_event_attr::sigtrap functionality relies on data->addr being
set. However commit 7b0846301531 ("perf: Use sample_flags for addr")
changed this to only initialize data->addr when not 0.

Fixes: 7b0846301531 ("perf: Use sample_flags for addr")
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/events/core.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9328,7 +9328,10 @@ static int __perf_event_overflow(struct
 			 */
 			WARN_ON_ONCE(event->pending_sigtrap != pending_id);
 		}
-		event->pending_addr = data->addr;
+
+		event->pending_addr = 0;
+		if (data->sample_flags & PERF_SAMPLE_ADDR)
+			event->pending_addr = data->addr;
 		irq_work_queue(&event->pending_irq);
 	}