From patchwork Wed Feb 9 12:33:03 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ingo Rohloff X-Patchwork-Id: 12740207 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C27AFC433F5 for ; Wed, 9 Feb 2022 12:33:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232418AbiBIMdL (ORCPT ); Wed, 9 Feb 2022 07:33:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59526 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233126AbiBIMdK (ORCPT ); Wed, 9 Feb 2022 07:33:10 -0500 Received: from smtp1.lauterbach.com (smtp1.lauterbach.com [62.154.241.196]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CA64EC05CB9B for ; Wed, 9 Feb 2022 04:33:13 -0800 (PST) Received: (qmail 15705 invoked by uid 484); 9 Feb 2022 12:33:12 -0000 X-Qmail-Scanner-Diagnostics: from ingpc2.intern.lauterbach.com by smtp1.lauterbach.com (envelope-from , uid 484) with qmail-scanner-2.11 (mhr: 1.0. clamdscan: 0.99/21437. spamassassin: 3.4.0. Clear:RC:1(10.2.10.44):. Processed in 0.064907 secs); 09 Feb 2022 12:33:12 -0000 Received: from ingpc2.intern.lauterbach.com (Authenticated_SSL:irohloff@[10.2.10.44]) (envelope-sender ) by smtp1.lauterbach.com (qmail-ldap-1.03) with TLS_AES_256_GCM_SHA384 encrypted SMTP for ; 9 Feb 2022 12:33:11 -0000 From: Ingo Rohloff To: gregkh@linuxfoundation.org, stern@rowland.harvard.edu Cc: linux-usb@vger.kernel.org, Ingo Rohloff Subject: [PATCH v2 1/1] USB: usbfs: Use a spinlock instead of atomic accesses to tally used memory. Date: Wed, 9 Feb 2022 13:33:03 +0100 Message-Id: <20220209123303.103340-2-ingo.rohloff@lauterbach.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20220209123303.103340-1-ingo.rohloff@lauterbach.com> References: <20220209123303.103340-1-ingo.rohloff@lauterbach.com> Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org While the existing code code imposes a limit on the used memory, it might be over pessimistic (even if this is unlikely). Example scenario: 8 threads running in parallel, all entering "usbfs_increase_memory_usage()" at the same time. The atomic accesses in "usbfs_increase_memory_usage()" could be serialized like this: 8 x "atomic64_add" 8 x "atomic64_read" If the 8 x "atomic64_add" raise "usbfs_memory_usage" above the limit, then all 8 calls of "usbfs_increase_memory_usage()" will return with -ENOMEM. If you instead serialize over the whole access to "usbfs_memory_usage" by using a spinlock, some of these calls will succeed. Signed-off-by: Ingo Rohloff Acked-by: Alan Stern --- drivers/usb/core/devio.c | 32 ++++++++++++++++++++++---------- 1 file changed, 22 insertions(+), 10 deletions(-) diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c index fa66e6e58792..6abb7294e919 100644 --- a/drivers/usb/core/devio.c +++ b/drivers/usb/core/devio.c @@ -139,30 +139,42 @@ MODULE_PARM_DESC(usbfs_memory_mb, /* Hard limit, necessary to avoid arithmetic overflow */ #define USBFS_XFER_MAX (UINT_MAX / 2 - 1000000) -static atomic64_t usbfs_memory_usage; /* Total memory currently allocated */ +static DEFINE_SPINLOCK(usbfs_memory_usage_lock); +static u64 usbfs_memory_usage; /* Total memory currently allocated */ /* Check whether it's okay to allocate more memory for a transfer */ static int usbfs_increase_memory_usage(u64 amount) { - u64 lim; + u64 lim, total_mem; + unsigned long flags; + int ret; lim = READ_ONCE(usbfs_memory_mb); lim <<= 20; - atomic64_add(amount, &usbfs_memory_usage); - - if (lim > 0 && atomic64_read(&usbfs_memory_usage) > lim) { - atomic64_sub(amount, &usbfs_memory_usage); - return -ENOMEM; - } + ret = 0; + spin_lock_irqsave(&usbfs_memory_usage_lock, flags); + total_mem = usbfs_memory_usage + amount; + if (lim > 0 && total_mem > lim) + ret = -ENOMEM; + else + usbfs_memory_usage = total_mem; + spin_unlock_irqrestore(&usbfs_memory_usage_lock, flags); - return 0; + return ret; } /* Memory for a transfer is being deallocated */ static void usbfs_decrease_memory_usage(u64 amount) { - atomic64_sub(amount, &usbfs_memory_usage); + unsigned long flags; + + spin_lock_irqsave(&usbfs_memory_usage_lock, flags); + if (amount > usbfs_memory_usage) + usbfs_memory_usage = 0; + else + usbfs_memory_usage -= amount; + spin_unlock_irqrestore(&usbfs_memory_usage_lock, flags); } static int connected(struct usb_dev_state *ps)