From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 045581AA793; Mon, 14 Oct 2024 15:10:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728918643; cv=none; b=u3en5flkZm7l9nx6kA0saUGX/NxsN1lV+98JP75leUlreJYzT8noeDuf5XdftTBDoG1//ky5O55VW4AHzt934STogmdZzEMRglpkmrLimpMhxu44lHc+xOBe+7d4yKUeluvaoAs/p9IuDpBB0KgGGdLsymqJhrUPwQuBHuXUMOs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728918643; c=relaxed/simple; bh=tdAq2HhBMnsCFK3pkFMBjmfHJbGwWHFr3BBHjhwIalo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=H/dOqAAsfOfePUqILV2TrKQyFm37CRLNjuPF/vnJ9Q7eeeW65yz4StNQu8Vdc4CSFT8nOFIlTmghJNL/p/STBf+QTU2znw51w06B1ocqop0366H4Tyf3Sa5uv1Xn7zBGsW7m0mdvHsBf8F68dLvmI+NyDl/TShZQ7CUWdDog7Rg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=S1c7AWH4; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="S1c7AWH4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 63572C4CEC3; Mon, 14 Oct 2024 15:10:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1728918642; bh=tdAq2HhBMnsCFK3pkFMBjmfHJbGwWHFr3BBHjhwIalo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=S1c7AWH4xVNMbHQxSnJDTJdmfBAin8cPqQbucMr+rQahIRwMCfgzuxwD1A0El9h3a Af4LgwrCZALaxYD9FdPvdeYXIVICXoD2Y8FtZZQoRcrOzVl5LWaQeRTyvhaOt+Wiwb RC2o7zoSHArnEGfDhe3yI5C65TJ1ZbC4B6Q5x/OA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Darrick J. Wong" , Klara Modin , "Peter Zijlstra (Intel)" , Sasha Levin Subject: [PATCH 6.1 380/798] jump_label: Fix static_key_slow_dec() yet again Date: Mon, 14 Oct 2024 16:15:34 +0200 Message-ID: <20241014141232.882481578@linuxfoundation.org> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20241014141217.941104064@linuxfoundation.org> References: <20241014141217.941104064@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Peter Zijlstra [ Upstream commit 1d7f856c2ca449f04a22d876e36b464b7a9d28b6 ] While commit 83ab38ef0a0b ("jump_label: Fix concurrency issues in static_key_slow_dec()") fixed one problem, it created yet another, notably the following is now possible: slow_dec if (try_dec) // dec_not_one-ish, false // enabled == 1 slow_inc if (inc_not_disabled) // inc_not_zero-ish // enabled == 2 return guard((mutex)(&jump_label_mutex); if (atomic_cmpxchg(1,0)==1) // false, we're 2 slow_dec if (try-dec) // dec_not_one, true // enabled == 1 return else try_dec() // dec_not_one, false WARN Use dec_and_test instead of cmpxchg(), like it was prior to 83ab38ef0a0b. Add a few WARNs for the paranoid. Fixes: 83ab38ef0a0b ("jump_label: Fix concurrency issues in static_key_slow_dec()") Reported-by: "Darrick J. Wong" Tested-by: Klara Modin Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Sasha Levin --- kernel/jump_label.c | 34 +++++++++++++++++++++++++++------- 1 file changed, 27 insertions(+), 7 deletions(-) diff --git a/kernel/jump_label.c b/kernel/jump_label.c index 7374053bbe049..554e04b25b13a 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -165,7 +165,7 @@ bool static_key_slow_inc_cpuslocked(struct static_key *key) jump_label_update(key); /* * Ensure that when static_key_fast_inc_not_disabled() or - * static_key_slow_try_dec() observe the positive value, + * static_key_dec_not_one() observe the positive value, * they must also observe all the text changes. */ atomic_set_release(&key->enabled, 1); @@ -247,7 +247,7 @@ void static_key_disable(struct static_key *key) } EXPORT_SYMBOL_GPL(static_key_disable); -static bool static_key_slow_try_dec(struct static_key *key) +static bool static_key_dec_not_one(struct static_key *key) { int v; @@ -271,6 +271,14 @@ static bool static_key_slow_try_dec(struct static_key *key) * enabled. This suggests an ordering problem on the user side. */ WARN_ON_ONCE(v < 0); + + /* + * Warn about underflow, and lie about success in an attempt to + * not make things worse. + */ + if (WARN_ON_ONCE(v == 0)) + return true; + if (v <= 1) return false; } while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v - 1))); @@ -281,15 +289,27 @@ static bool static_key_slow_try_dec(struct static_key *key) static void __static_key_slow_dec_cpuslocked(struct static_key *key) { lockdep_assert_cpus_held(); + int val; - if (static_key_slow_try_dec(key)) + if (static_key_dec_not_one(key)) return; guard(mutex)(&jump_label_mutex); - if (atomic_cmpxchg(&key->enabled, 1, 0) == 1) + val = atomic_read(&key->enabled); + /* + * It should be impossible to observe -1 with jump_label_mutex held, + * see static_key_slow_inc_cpuslocked(). + */ + if (WARN_ON_ONCE(val == -1)) + return; + /* + * Cannot already be 0, something went sideways. + */ + if (WARN_ON_ONCE(val == 0)) + return; + + if (atomic_dec_and_test(&key->enabled)) jump_label_update(key); - else - WARN_ON_ONCE(!static_key_slow_try_dec(key)); } static void __static_key_slow_dec(struct static_key *key) @@ -326,7 +346,7 @@ void __static_key_slow_dec_deferred(struct static_key *key, { STATIC_KEY_CHECK_USE(key); - if (static_key_slow_try_dec(key)) + if (static_key_dec_not_one(key)) return; schedule_delayed_work(work, timeout); -- 2.43.0