From patchwork Wed Nov 4 08:15:47 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Juergen Gross X-Patchwork-Id: 11879811 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 EBEDD921 for ; Wed, 4 Nov 2020 08:16:32 +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 AF11C206C0 for ; Wed, 4 Nov 2020 08:16:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="dQMJ2oPy" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AF11C206C0 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.18837.43874 (Exim 4.92) (envelope-from ) id 1kaDxY-0000VD-9d; Wed, 04 Nov 2020 08:16:00 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 18837.43874; Wed, 04 Nov 2020 08:16:00 +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 1kaDxY-0000V1-5H; Wed, 04 Nov 2020 08:16:00 +0000 Received: by outflank-mailman (input) for mailman id 18837; Wed, 04 Nov 2020 08:15:59 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kaDxW-0000Pk-Vc for xen-devel@lists.xenproject.org; Wed, 04 Nov 2020 08:15:59 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTP id b17a3e08-d071-4107-9a9a-62c7dbc0f131; Wed, 04 Nov 2020 08:15:51 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 7FB21AC23; Wed, 4 Nov 2020 08:15:51 +0000 (UTC) Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kaDxW-0000Pk-Vc for xen-devel@lists.xenproject.org; Wed, 04 Nov 2020 08:15:59 +0000 X-Inumbo-ID: b17a3e08-d071-4107-9a9a-62c7dbc0f131 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTP id b17a3e08-d071-4107-9a9a-62c7dbc0f131; Wed, 04 Nov 2020 08:15:51 +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=1604477751; 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=SMWFDeqyO4Bqdr2XBTO3XuyCVTVJJjcu3BY2gEaI7+0=; b=dQMJ2oPyWtwflpsHfulQPgBtMzNX2MQIF21kPA26/35M0xKeNVqjfq6c1xWMK+m7FDKPmO zTkXnEpzbTzej/zjlWVmri5+f9+2ho75oKOVO5iLV2UpYlv0DIsdpbOhc4fbUE+C2eYeKV FCc72zmaABiCECj/knpDXrloiKhgKD0= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 7FB21AC23; Wed, 4 Nov 2020 08:15:51 +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 v3 1/3] xen/spinlocks: spin_trylock with interrupts off is always fine Date: Wed, 4 Nov 2020 09:15:47 +0100 Message-Id: <20201104081549.3712-2-jgross@suse.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20201104081549.3712-1-jgross@suse.com> References: <20201104081549.3712-1-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 Acked-by: Julien Grall --- V2: - corrected comment (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..b4aaf6bce6 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() with interrupts off is always fine, as this 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) ) {