From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 78D1F48C8C4; Tue, 6 Oct 2026 14:57:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791298675; cv=none; b=lWUM1oUe7CZilZOZXvDaKstsR+whl77ffv5RKeT7jHq7JSdJiMCss70TUTU6/xj8vl4BZB3pWjItEyta6kBKOYRjDnS7Tjxkh2sl4EGNjz9Td2Bcafet5sDNFhkZz10wErNeoZZXIk8SN/XNs+i9mRmz5ZHQ4v9FoePSJioJ7NU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791298675; c=relaxed/simple; bh=YqEtDNP2HV0mLPxH10/gbf1H72RTgVr948823/q4Boo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=kOsTaxgtj6kbbBrm7LlacE1HZJqmDfYv4Z9b3uTeHKjZ5UMRbDy9eyVgXcoxgnNYMPI7zshHswkcjPJnMFfIcPGzDqPk8EpgJtvweBr/YkGQDiP7YXhZGFmBid+3zHbc7FsIbQ949pFjS6d18v/qhC0/Oz2yjgzzS5wtAznIpas= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IMweqZoh; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="IMweqZoh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 46CBF1F0089B; Tue, 6 Oct 2026 14:57:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791298674; bh=BgRyqkmROtB9xJY3E+pxWBtSxAVsrJ/0mFxXQxPkYng=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=IMweqZohtXAzytIdRZPZE53JbwUB0FqOj13hqAIZWjGSltAjFrFkhzv/GqfnqTI7q 1CJRNHiVt28ndrZAiA2a+mNUXrOWETWUNGbAtmQzAxgGHQ6dYnfnzvySwRGeqJqnd4 9tcv1mMIPVKPslxuNqQ6fZ1TtNEjNy554ZYWIDbRRjkpju8nR1y3L9yerfVVzWuxe+ NeOh5V28eVxE4yCCZRzf1iLkc8pIRTTV/nPUvVp0Rq3mXyVhC2088oxiZDaNODe/ms 9Lhplr2CzPKrTK3dK1YSEBlQUzWdpvJG0LxuJ91mjjqp9Lt/lrC6mtcys3+QGme1zp nAsR1ANxJjPWQ== From: Arnaldo Carvalho de Melo To: Namhyung Kim Cc: Ingo Molnar , Thomas Gleixner , James Clark , Jiri Olsa , Ian Rogers , Adrian Hunter , Clark Williams , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Arnaldo Carvalho de Melo Subject: [PATCH 4/8] perf mutex: Add DO_ONCE() for one-time initialization Date: Tue, 6 Oct 2026 16:57:25 +0200 Message-ID: <20261006145729.3028247-5-acme@kernel.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20261006145729.3028247-1-acme@kernel.org> References: <20261006145729.3028247-1-acme@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Arnaldo Carvalho de Melo For lazy init that more than one thread can race into, without pthread_once() so that it stays within perf's locking primitives and clang's -Wthread-safety keeps an eye on the mutexes involved. Mirrors the kernel's include/linux/once.h DO_ONCE(), dropping its static key fast path, unnecessary at these cold init paths: a per call site static bool plus a statically initialized mutex, double checked. As there, code reachable from more than one call site must go through a common helper. The lockless fast path reads ___done with an acquire, paired with a release store after fn(), so that fn()'s side effects are visible to threads taking the fast path, which the dropped static key used to guarantee. The __atomic builtins are used rather than smp_load_acquire()/ smp_store_release() because ThreadSanitizer understands them, avoiding reports on ___done and on what fn() initialized. Assisted-by: LLM Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/mutex.h | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/tools/perf/util/mutex.h b/tools/perf/util/mutex.h index fe04db21d19c5b0b..5554937675886ef3 100644 --- a/tools/perf/util/mutex.h +++ b/tools/perf/util/mutex.h @@ -104,6 +104,30 @@ struct LOCKABLE mutex { #endif #define DEFINE_MUTEX(name) struct mutex name = { .lock = __PERF_MUTEX_INITIALIZER } +/* + * Runs fn() exactly once however many threads race to it, the rest wait + * for it to finish; per call site state, so multiple sites wanting the + * same once use a common helper, as in the kernel's DO_ONCE(). + */ +#define DO_ONCE(fn, ...) \ + ({ \ + static bool ___done; \ + static DEFINE_MUTEX(___once_lock); \ + bool ___ret = false; \ + \ + if (!__atomic_load_n(&___done, __ATOMIC_ACQUIRE)) { \ + mutex_lock(&___once_lock); \ + if (!___done) { \ + fn(__VA_ARGS__); \ + __atomic_store_n(&___done, true, \ + __ATOMIC_RELEASE); \ + ___ret = true; \ + } \ + mutex_unlock(&___once_lock); \ + } \ + ___ret; \ + }) + /* A wrapper around the condition variable implementation. */ struct cond { pthread_cond_t cond; -- 2.55.0