From patchwork Fri Oct 30 14:24:59 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: =?utf-8?b?SsO8cmdlbiBHcm/Dnw==?= X-Patchwork-Id: 11869829 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id DE0C261C for ; Fri, 30 Oct 2020 14:25:46 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9CF9D2076E for ; Fri, 30 Oct 2020 14:25:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="d/9UWwuO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9CF9D2076E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.15900.39151 (Exim 4.92) (envelope-from ) id 1kYVL4-0000km-FG; Fri, 30 Oct 2020 14:25:10 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 15900.39151; Fri, 30 Oct 2020 14:25:10 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kYVL4-0000kc-CC; Fri, 30 Oct 2020 14:25:10 +0000 Received: by outflank-mailman (input) for mailman id 15900; Fri, 30 Oct 2020 14:25:09 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kYVL2-0000hB-Vc for xen-devel@lists.xenproject.org; Fri, 30 Oct 2020 14:25:09 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 24413e0e-f2b8-46c8-9fe3-74a28d1bb41c; Fri, 30 Oct 2020 14:25:03 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 8B54DABD1; Fri, 30 Oct 2020 14:25:02 +0000 (UTC) Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kYVL2-0000hB-Vc for xen-devel@lists.xenproject.org; Fri, 30 Oct 2020 14:25:09 +0000 X-Inumbo-ID: 24413e0e-f2b8-46c8-9fe3-74a28d1bb41c Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 24413e0e-f2b8-46c8-9fe3-74a28d1bb41c; Fri, 30 Oct 2020 14:25:03 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1604067902; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=5gKiiKos/dApKc2beKCGTAc1Rx9gih7YAhJwI1zCh3E=; b=d/9UWwuOw44S/0Dnua9hZLPFL7oLqVNAb6BTZa6QwkYJ0D1sZjhA5BcwZuVfRjyVjmB+H4 tfVeMSdkw8Lb6za77huWQFmYYTigKHXzx6l6Q1MbhWdBUn9kth+zK6IT39V9tzca7ZRbgD W0HV+jHxh7DD1JXdWX98sKXFxX36Kck= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 8B54DABD1; Fri, 30 Oct 2020 14:25:02 +0000 (UTC) From: Juergen Gross To: xen-devel@lists.xenproject.org Cc: Juergen Gross , Andrew Cooper , George Dunlap , Ian Jackson , Jan Beulich , Julien Grall , Stefano Stabellini , Wei Liu Subject: [PATCH 1/2] xen/spinlocks: spin_trylock with interrupts off is always fine Date: Fri, 30 Oct 2020 15:24:59 +0100 Message-Id: <20201030142500.5464-2-jgross@suse.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20201030142500.5464-1-jgross@suse.com> References: <20201030142500.5464-1-jgross@suse.com> MIME-Version: 1.0 Even if a spinlock was taken with interrupts on before calling spin_trylock() with interrupts off is fine, as it can't block. Add a bool parameter "try" to check_lock() for handling this case. Remove the call of check_lock() from _spin_is_locked(), as it really serves no purpose and it can even lead to false crashes, e.g. when a lock was taken correctly with interrupts enabled and the call of _spin_is_locked() happened with interrupts off. In case the lock is taken with wrong interrupt flags this will be catched when taking the lock. Signed-off-by: Juergen Gross Reviewed-by: Jan Beulich --- xen/common/spinlock.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c index ce3106e2d3..54f0c55dc2 100644 --- a/xen/common/spinlock.c +++ b/xen/common/spinlock.c @@ -13,7 +13,7 @@ static atomic_t spin_debug __read_mostly = ATOMIC_INIT(0); -static void check_lock(union lock_debug *debug) +static void check_lock(union lock_debug *debug, bool try) { bool irq_safe = !local_irq_is_enabled(); @@ -42,7 +42,13 @@ static void check_lock(union lock_debug *debug) * * To guard against this subtle bug we latch the IRQ safety of every * spinlock in the system, on first use. + * + * A spin_trylock() or spin_is_locked() with interrupts off is always + * fine, as those can't block and above deadlock scenario doesn't apply. */ + if ( try && irq_safe ) + return; + if ( unlikely(debug->irq_safe != irq_safe) ) { union lock_debug seen, new = { 0 }; @@ -102,7 +108,7 @@ void spin_debug_disable(void) #else /* CONFIG_DEBUG_LOCKS */ -#define check_lock(l) ((void)0) +#define check_lock(l, t) ((void)0) #define check_barrier(l) ((void)0) #define got_lock(l) ((void)0) #define rel_lock(l) ((void)0) @@ -159,7 +165,7 @@ void inline _spin_lock_cb(spinlock_t *lock, void (*cb)(void *), void *data) spinlock_tickets_t tickets = SPINLOCK_TICKET_INC; LOCK_PROFILE_VAR; - check_lock(&lock->debug); + check_lock(&lock->debug, false); preempt_disable(); tickets.head_tail = arch_fetch_and_add(&lock->tickets.head_tail, tickets.head_tail); @@ -220,8 +226,6 @@ void _spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags) int _spin_is_locked(spinlock_t *lock) { - check_lock(&lock->debug); - /* * Recursive locks may be locked by another CPU, yet we return * "false" here, making this function suitable only for use in @@ -236,7 +240,7 @@ int _spin_trylock(spinlock_t *lock) { spinlock_tickets_t old, new; - check_lock(&lock->debug); + check_lock(&lock->debug, true); old = observe_lock(&lock->tickets); if ( old.head != old.tail ) return 0; @@ -294,7 +298,7 @@ int _spin_trylock_recursive(spinlock_t *lock) BUILD_BUG_ON(NR_CPUS > SPINLOCK_NO_CPU); BUILD_BUG_ON(SPINLOCK_RECURSE_BITS < 3); - check_lock(&lock->debug); + check_lock(&lock->debug, true); if ( likely(lock->recurse_cpu != cpu) ) {