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 A72AD3FA5F8; Sun, 4 Oct 2026 06:05:22 +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=1791093924; cv=none; b=VXe5NWiV+SLXAgRuJVngN3wHa2K+R6RC9sAWs2uUd6V3VD2vaGjYG9YPGim3Wq++QVxPZFY5HcDIhXoem6UMYL4+3BHnvMcauFnuA7LVcbe0s+PxNpjj6TN2Ts2CjluJL8U/wZFMtUwXEj6pzR/TCgrvNfvX89LL8Q1CKKPB8MI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791093924; c=relaxed/simple; bh=YqEtDNP2HV0mLPxH10/gbf1H72RTgVr948823/q4Boo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Rp0p8uI461Etc6JXJlzPQLOyvCsnsH56D/B1lrIhaWIaol4gy0MT0JZjZ/gxZHyhfUOHyH95SC5p5VEga67rxUhUpfvZNGd/EPfNUxJQoxJVfcM1aP1f4P0D9M8JWeDm2d6SAHkfVOactbjC6cLUq3B1QlmKCT00jESuM2nNd2o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kgzBJoHz; 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="kgzBJoHz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 584901F000FF; Sun, 4 Oct 2026 06:05:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791093922; bh=BgRyqkmROtB9xJY3E+pxWBtSxAVsrJ/0mFxXQxPkYng=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=kgzBJoHzty2L9FUbaCG2YQxQJKDKiD2XHgA5Aabd35PC7+RYuasqTeE4E0CD4gqtE V+uksacm1onulOk9GF5O3HnQt6a1nbkzbkv0xiyvnqsWpTKnZK3knomTjqbXbjOqsF fp5ojj/glwXjFH9BB+2eY4BQukLHoElNFofSAVhUEX+Uk45pQwx4KtOZgdjioU36By pfJlyY2R3JY8fQVwWqyizFChEBGwLqbXuPe83KNOBaH6uXfeknQwXWj3YD+Yy2EjpW ZTWd4zgQU9cs1Ef/NoRmsCiUxfOXfPCSuyucBol19//lW37CzQxppLRuVE9Fj8XkpW Kx1dAkX4Z853w== 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 v9 4/9] perf mutex: Add DO_ONCE() for one-time initialization Date: Sun, 4 Oct 2026 08:04:51 +0200 Message-ID: <20261004060457.3353-5-acme@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20261004060457.3353-1-acme@kernel.org> References: <20261004060457.3353-1-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