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 993D9192594; Tue, 8 Oct 2024 12:39:02 +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=1728391142; cv=none; b=kVm+EaaX+G1zR3kpvXAO40PTysxNXrn269ft4j/IvwrnmRJqycapeKdQA1DzwsP4Tsk3UdblbaTzGEJ8CKqUXuZNyLGSHv7oRWmoUDaaYHsZ5J/cRqYceWYfulgnbO0xpmASaxkN5g9lMTOEBLYgLVd2uAl52v+ZmPDtaWsGwyk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728391142; c=relaxed/simple; bh=cavsj7dCJZlhWTt3pOAnuQlRwEfajGzNU/QJ2ECclAA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RwcT3tw8ir8EuAgFztZnagakBcB1EIWN7tF6f9TSCnGypNjLUBgxKEjNp98ERndK6F4nx1Y9zpwjeBLWWmlSM2F0HVVowgyDH+UqoT2RGaVOjU9XvxrxWa8Kg399SSIuc3e+LFQggm1SUuRvBefSpFVbB9W4pOD19pAnnOtUpK8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=1FCbCrsV; 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="1FCbCrsV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 00C0FC4CEC7; Tue, 8 Oct 2024 12:39:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1728391142; bh=cavsj7dCJZlhWTt3pOAnuQlRwEfajGzNU/QJ2ECclAA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1FCbCrsVhTHIlAG4B/x+CnsdS5YBlc4LfWkrLiz0kl0jHFXq1HsIZQgT3VD3E5l4a b7WM72QnWb9NGnqFEqYFOUO341K9hPU4PgQlzriuf9vSYvZ3nMXpzsrp1uQEEQo0zR p8TUQLwLGbUmS2Vw2qH0rv04yh4qRHmN64/Q0T8k= 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 6.11 003/558] jump_label: Fix static_key_slow_dec() yet again Date: Tue, 8 Oct 2024 14:00:33 +0200 Message-ID: <20241008115702.356969408@linuxfoundation.org> X-Mailer: git-send-email 2.46.2 In-Reply-To: <20241008115702.214071228@linuxfoundation.org> References: <20241008115702.214071228@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.11-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 6dc76b590703e..93a822d3c468c 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -168,7 +168,7 @@ 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); @@ -250,7 +250,7 @@ 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; @@ -274,6 +274,14 @@ 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))); @@ -284,15 +292,27 @@ 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) @@ -329,7 +349,7 @@ 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