linux-kernel - [tip: perf/core] perf: Identify the 0->1 transition for event::mmap

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Message-ID: <175551254020.1420.9814271943292016323.tip-bot2@tip-bot2>
Date: Mon, 18 Aug 2025 10:22:20 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: perf/core] perf: Identify the 0->1 transition for event::mmap_count

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     59741451b49ce9964a9758c19d6f7df2a1255c75
Gitweb:        https://git.kernel.org/tip/59741451b49ce9964a9758c19d6f7df2a1255c75
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Tue, 12 Aug 2025 12:39:12 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 15 Aug 2025 13:13:02 +02:00

perf: Identify the 0->1 transition for event::mmap_count

Needed because refcount_inc() doesn't allow the 0->1 transition.

Specifically, this is the case where we've created the RB, this means
there was no RB, and as such there could not have been an mmap.
Additionally we hold mmap_mutex to serialize everything.

This must be the first.

Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/r/20250812104019.956479989@infradead.org
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 41941df..f6211ab 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7034,7 +7034,7 @@ static int perf_mmap_rb(struct vm_area_struct *vma, struct perf_event *event,
 	perf_event_update_userpage(event);
 
 	perf_mmap_account(vma, user_extra, extra);
-	atomic_inc(&event->mmap_count);
+	atomic_set(&event->mmap_count, 1);
 
 	return 0;
 }