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[209.132.180.67]) by mx.google.com with ESMTP id l34si4184648pgb.574.2019.05.09.11.57.51; Thu, 09 May 2019 11:57:52 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b="gj5VXeE/"; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728927AbfEIS5v (ORCPT + 30 others); Thu, 9 May 2019 14:57:51 -0400 Received: from mail.kernel.org ([198.145.29.99]:48374 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728945AbfEISxt (ORCPT ); Thu, 9 May 2019 14:53:49 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 459ED217D6; Thu, 9 May 2019 18:53:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1557428028; bh=M/WflKJ18bUUTjs4bfqR6PSZ0fvoLlGIFcH8OVmjCno=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=gj5VXeE/cLonRAG/6WopegWBQfw6kA3W6tKpSincKQ5hL4soJ/yjiBsPC5ez8XoXV 8Id9oCSDG0HdC1EPQyuUSQ7SoiswNg1Txm3dlvEWu6Lv9cA9aI6QrfRNnsq162xGfr mPvK+IspiSOut3pXXDE0J6QhW1My6LfBG7dR06KE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, stable@kernel.org, Will Deacon Subject: [PATCH 5.0 95/95] arm64: futex: Bound number of LDXR/STXR loops in FUTEX_WAKE_OP Date: Thu, 9 May 2019 20:42:52 +0200 Message-Id: <20190509181315.815947588@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190509181309.180685671@linuxfoundation.org> References: <20190509181309.180685671@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Will Deacon commit 03110a5cb2161690ae5ac04994d47ed0cd6cef75 upstream. Our futex implementation makes use of LDXR/STXR loops to perform atomic updates to user memory from atomic context. This can lead to latency problems if we end up spinning around the LL/SC sequence at the expense of doing something useful. Rework our futex atomic operations so that we return -EAGAIN if we fail to update the futex word after 128 attempts. The core futex code will reschedule if necessary and we'll try again later. Cc: Fixes: 6170a97460db ("arm64: Atomic operations") Signed-off-by: Will Deacon Signed-off-by: Greg Kroah-Hartman --- arch/arm64/include/asm/futex.h | 55 +++++++++++++++++++++++++---------------- 1 file changed, 34 insertions(+), 21 deletions(-) --- a/arch/arm64/include/asm/futex.h +++ b/arch/arm64/include/asm/futex.h @@ -23,26 +23,34 @@ #include +#define FUTEX_MAX_LOOPS 128 /* What's the largest number you can think of? */ + #define __futex_atomic_op(insn, ret, oldval, uaddr, tmp, oparg) \ do { \ + unsigned int loops = FUTEX_MAX_LOOPS; \ + \ uaccess_enable(); \ asm volatile( \ " prfm pstl1strm, %2\n" \ "1: ldxr %w1, %2\n" \ insn "\n" \ "2: stlxr %w0, %w3, %2\n" \ -" cbnz %w0, 1b\n" \ -" dmb ish\n" \ +" cbz %w0, 3f\n" \ +" sub %w4, %w4, %w0\n" \ +" cbnz %w4, 1b\n" \ +" mov %w0, %w7\n" \ "3:\n" \ +" dmb ish\n" \ " .pushsection .fixup,\"ax\"\n" \ " .align 2\n" \ -"4: mov %w0, %w5\n" \ +"4: mov %w0, %w6\n" \ " b 3b\n" \ " .popsection\n" \ _ASM_EXTABLE(1b, 4b) \ _ASM_EXTABLE(2b, 4b) \ - : "=&r" (ret), "=&r" (oldval), "+Q" (*uaddr), "=&r" (tmp) \ - : "r" (oparg), "Ir" (-EFAULT) \ + : "=&r" (ret), "=&r" (oldval), "+Q" (*uaddr), "=&r" (tmp), \ + "+r" (loops) \ + : "r" (oparg), "Ir" (-EFAULT), "Ir" (-EAGAIN) \ : "memory"); \ uaccess_disable(); \ } while (0) @@ -57,23 +65,23 @@ arch_futex_atomic_op_inuser(int op, int switch (op) { case FUTEX_OP_SET: - __futex_atomic_op("mov %w3, %w4", + __futex_atomic_op("mov %w3, %w5", ret, oldval, uaddr, tmp, oparg); break; case FUTEX_OP_ADD: - __futex_atomic_op("add %w3, %w1, %w4", + __futex_atomic_op("add %w3, %w1, %w5", ret, oldval, uaddr, tmp, oparg); break; case FUTEX_OP_OR: - __futex_atomic_op("orr %w3, %w1, %w4", + __futex_atomic_op("orr %w3, %w1, %w5", ret, oldval, uaddr, tmp, oparg); break; case FUTEX_OP_ANDN: - __futex_atomic_op("and %w3, %w1, %w4", + __futex_atomic_op("and %w3, %w1, %w5", ret, oldval, uaddr, tmp, ~oparg); break; case FUTEX_OP_XOR: - __futex_atomic_op("eor %w3, %w1, %w4", + __futex_atomic_op("eor %w3, %w1, %w5", ret, oldval, uaddr, tmp, oparg); break; default: @@ -93,6 +101,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 oldval, u32 newval) { int ret = 0; + unsigned int loops = FUTEX_MAX_LOOPS; u32 val, tmp; u32 __user *uaddr; @@ -104,20 +113,24 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, asm volatile("// futex_atomic_cmpxchg_inatomic\n" " prfm pstl1strm, %2\n" "1: ldxr %w1, %2\n" -" sub %w3, %w1, %w4\n" -" cbnz %w3, 3f\n" -"2: stlxr %w3, %w5, %2\n" -" cbnz %w3, 1b\n" -" dmb ish\n" +" sub %w3, %w1, %w5\n" +" cbnz %w3, 4f\n" +"2: stlxr %w3, %w6, %2\n" +" cbz %w3, 3f\n" +" sub %w4, %w4, %w3\n" +" cbnz %w4, 1b\n" +" mov %w0, %w8\n" "3:\n" +" dmb ish\n" +"4:\n" " .pushsection .fixup,\"ax\"\n" -"4: mov %w0, %w6\n" -" b 3b\n" +"5: mov %w0, %w7\n" +" b 4b\n" " .popsection\n" - _ASM_EXTABLE(1b, 4b) - _ASM_EXTABLE(2b, 4b) - : "+r" (ret), "=&r" (val), "+Q" (*uaddr), "=&r" (tmp) - : "r" (oldval), "r" (newval), "Ir" (-EFAULT) + _ASM_EXTABLE(1b, 5b) + _ASM_EXTABLE(2b, 5b) + : "+r" (ret), "=&r" (val), "+Q" (*uaddr), "=&r" (tmp), "+r" (loops) + : "r" (oldval), "r" (newval), "Ir" (-EFAULT), "Ir" (-EAGAIN) : "memory"); uaccess_disable();