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 26B90187FFB; Tue, 30 Jul 2024 16:04:50 +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=1722355490; cv=none; b=rlvN+tMKpZNAYmfdOELxBaFPUcVxkP63lpKyipe+4+O7omppNR+45kqw+JLDZhAbDbX7277PB8fHuycfVpTwlgyMKnIyKbx64n/P2BbDjSjwaGeXwKx6C5dzHWqmnTRGh5bEGmUoYssOwITtGW58P3+SNt8g2BMQX94nPZWbY1w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722355490; c=relaxed/simple; bh=ivRllV5663+MgRxBlNVeFwexOpt12L4Jl2ek9YEKYLA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ZKiRTdT654q1hu4NE4JlaFefKujw656DBTKWBHJyd4bU4+mT9UlbeH/sMOVdLEhjhBoLiTbPhqOjl5XJKrQoRa7BwChRfPHMDydlpG8eLN7OOdhYyLurZd0dWavETqsQVty/gozW+pOkSR0ITdUdRilAQ4TrhDsiLbIIE5vpUZY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=dVlR0bZs; 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="dVlR0bZs" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6CA73C4AF0E; Tue, 30 Jul 2024 16:04:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1722355490; bh=ivRllV5663+MgRxBlNVeFwexOpt12L4Jl2ek9YEKYLA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dVlR0bZs8D2w9jcD9dINykIQqaa5NkzNstXW7EF/xtdhZvntuv7IeqnDOCsCxkyCN ljn9j8xrFEaw4M8ZQuBiUBFiBPO7U45Kxnk3q77A0+rQVNXLDD1jTWGzkxKiUNt7k8 CXqoo67xoOfmtN82qGc9cI//jDhKHLS49mRx0SP8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yue Sun , Xingwei Lee , Thomas Gleixner , "Peter Zijlstra (Intel)" , Sasha Levin Subject: [PATCH 6.1 099/440] jump_label: Fix concurrency issues in static_key_slow_dec() Date: Tue, 30 Jul 2024 17:45:32 +0200 Message-ID: <20240730151619.753507378@linuxfoundation.org> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240730151615.753688326@linuxfoundation.org> References: <20240730151615.753688326@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: Thomas Gleixner [ Upstream commit 83ab38ef0a0b2407d43af9575bb32333fdd74fb2 ] The commit which tried to fix the concurrency issues of concurrent static_key_slow_inc() failed to fix the equivalent issues vs. static_key_slow_dec(): CPU0 CPU1 static_key_slow_dec() static_key_slow_try_dec() key->enabled == 1 val = atomic_fetch_add_unless(&key->enabled, -1, 1); if (val == 1) return false; jump_label_lock(); if (atomic_dec_and_test(&key->enabled)) { --> key->enabled == 0 __jump_label_update() static_key_slow_dec() static_key_slow_try_dec() key->enabled == 0 val = atomic_fetch_add_unless(&key->enabled, -1, 1); --> key->enabled == -1 <- FAIL There is another bug in that code, when there is a concurrent static_key_slow_inc() which enables the key as that sets key->enabled to -1 so on the other CPU val = atomic_fetch_add_unless(&key->enabled, -1, 1); will succeed and decrement to -2, which is invalid. Cure all of this by replacing the atomic_fetch_add_unless() with a atomic_try_cmpxchg() loop similar to static_key_fast_inc_not_disabled(). [peterz: add WARN_ON_ONCE for the -1 race] Fixes: 4c5ea0a9cd02 ("locking/static_key: Fix concurrent static_key_slow_inc()") Reported-by: Yue Sun Reported-by: Xingwei Lee Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20240610124406.422897838@linutronix.de Signed-off-by: Sasha Levin --- kernel/jump_label.c | 45 +++++++++++++++++++++++++++++---------------- 1 file changed, 29 insertions(+), 16 deletions(-) diff --git a/kernel/jump_label.c b/kernel/jump_label.c index d9c822bbffb8d..eec802175ccc6 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -131,7 +131,7 @@ bool static_key_fast_inc_not_disabled(struct static_key *key) STATIC_KEY_CHECK_USE(key); /* * Negative key->enabled has a special meaning: it sends - * static_key_slow_inc() down the slow path, and it is non-zero + * static_key_slow_inc/dec() down the slow path, and it is non-zero * so it counts as "enabled" in jump_label_update(). Note that * atomic_inc_unless_negative() checks >= 0, so roll our own. */ @@ -150,7 +150,7 @@ bool static_key_slow_inc_cpuslocked(struct static_key *key) lockdep_assert_cpus_held(); /* - * Careful if we get concurrent static_key_slow_inc() calls; + * Careful if we get concurrent static_key_slow_inc/dec() calls; * later calls must wait for the first one to _finish_ the * jump_label_update() process. At the same time, however, * the jump_label_update() call below wants to see @@ -247,20 +247,32 @@ EXPORT_SYMBOL_GPL(static_key_disable); static bool static_key_slow_try_dec(struct static_key *key) { - int val; - - val = atomic_fetch_add_unless(&key->enabled, -1, 1); - if (val == 1) - return false; + int v; /* - * The negative count check is valid even when a negative - * key->enabled is in use by static_key_slow_inc(); a - * __static_key_slow_dec() before the first static_key_slow_inc() - * returns is unbalanced, because all other static_key_slow_inc() - * instances block while the update is in progress. + * Go into the slow path if key::enabled is less than or equal than + * one. One is valid to shut down the key, anything less than one + * is an imbalance, which is handled at the call site. + * + * That includes the special case of '-1' which is set in + * static_key_slow_inc_cpuslocked(), but that's harmless as it is + * fully serialized in the slow path below. By the time this task + * acquires the jump label lock the value is back to one and the + * retry under the lock must succeed. */ - WARN(val < 0, "jump label: negative count!\n"); + v = atomic_read(&key->enabled); + do { + /* + * Warn about the '-1' case though; since that means a + * decrement is concurrent with a first (0->1) increment. IOW + * people are trying to disable something that wasn't yet fully + * enabled. This suggests an ordering problem on the user side. + */ + WARN_ON_ONCE(v < 0); + if (v <= 1) + return false; + } while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v - 1))); + return true; } @@ -271,10 +283,11 @@ static void __static_key_slow_dec_cpuslocked(struct static_key *key) if (static_key_slow_try_dec(key)) return; - jump_label_lock(); - if (atomic_dec_and_test(&key->enabled)) + guard(mutex)(&jump_label_mutex); + if (atomic_cmpxchg(&key->enabled, 1, 0)) jump_label_update(key); - jump_label_unlock(); + else + WARN_ON_ONCE(!static_key_slow_try_dec(key)); } static void __static_key_slow_dec(struct static_key *key) -- 2.43.0