From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [134.134.136.31]) (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 B8887802 for ; Wed, 10 Jan 2024 00:52:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="HYEa8Xcg" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1704847932; x=1736383932; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=P1lrP9NOMqRhHmYOJ4SIwEz/KxAXtMJkZlm7Bn8S+QQ=; b=HYEa8XcgC4peygMcUp/7CZFxbhnMMKvSmAVZPC8pXiGUWd0yJtHd4/tF EwnK/eQ+W4Wl52gkxHL+dmwJQHOQ9JBNZdSocV8PK/Y9YRzyYILr3qXrM 55RrC1w107k0CDbixa8bcDTFP641Ire/8yh5nrhzYCi32GHEYFSkSKgv4 KmfIHKykHKaQEipaVJpaK+4bG1u5LoVfPAnnYvV9MVQCp0Ndtf6T1++Gj /MTiBCU3v4b78RggJJri2oRzy81hmlEYIym+q4bR2jsvgeJGzmQqi0/FT LWFblCoS1aB7U1PtnPA0hcs2W+CjSaAZjmkGco8QCO+8iLThdMeXb1AbX A==; X-IronPort-AV: E=McAfee;i="6600,9927,10947"; a="462654467" X-IronPort-AV: E=Sophos;i="6.04,184,1695711600"; d="scan'208";a="462654467" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Jan 2024 16:52:12 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10947"; a="1028964191" X-IronPort-AV: E=Sophos;i="6.04,184,1695711600"; d="scan'208";a="1028964191" Received: from zhaohaif-mobl.ccr.corp.intel.com (HELO [10.93.19.162]) ([10.93.19.162]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Jan 2024 16:52:08 -0800 Message-ID: <252396e4-bf9a-4655-8993-75a44d58febd@linux.intel.com> Date: Wed, 10 Jan 2024 08:52:06 +0800 Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 0/2] iommu/iova: Make the rcache depot properly flexible To: Robin Murphy , Ido Schimmel Cc: joro@8bytes.org, will@kernel.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, zhangzekun11@huawei.com, john.g.garry@oracle.com, dheerajkumar.srivastava@amd.com, jsnitsel@redhat.com References: <15a058ba-3b51-46f3-bb1c-23792d100b55@linux.intel.com> <7eaa0f41-a71b-43c1-8596-1df99584530a@arm.com> From: Ethan Zhao In-Reply-To: <7eaa0f41-a71b-43c1-8596-1df99584530a@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 1/9/2024 7:26 PM, Robin Murphy wrote: > On 2024-01-09 6:23 am, Ethan Zhao wrote: >> >> On 1/9/2024 1:54 PM, Ethan Zhao wrote: >>> >>> On 1/9/2024 1:35 AM, Robin Murphy wrote: >>>> On 2023-12-28 12:23 pm, Ido Schimmel wrote: >>>>> On Tue, Sep 12, 2023 at 05:28:04PM +0100, Robin Murphy wrote: >>>>>> v2: >>>>>> https://lore.kernel.org/linux-iommu/cover.1692641204.git.robin.murphy@arm.com/ >>>>>> >>>>>> Hi all, >>>>>> >>>>>> I hope this is good to go now, just fixed the locking (and threw >>>>>> lockdep at it to confirm, which of course I should have done to >>>>>> begin >>>>>> with...) and picked up tags. >>>>> >>>>> Hi, >>>>> >>>>> After pulling the v6.7 changes we started seeing the following memory >>>>> leaks [1] of 'struct iova_magazine'. I'm not sure how to reproduce >>>>> it, >>>>> which is why I didn't perform bisection. However, looking at the >>>>> mentioned code paths, they seem to have been changed in v6.7 as >>>>> part of >>>>> this patchset. I reverted both patches and didn't see any memory >>>>> leaks >>>>> when running a full regression (~10 hours), but I will repeat it >>>>> to be >>>>> sure. >>>>> >>>>> Any idea what could be the problem? >>>> >>>> Hmm, we've got what looks to be a set of magazines forming a >>>> plausible depot list (or at least the tail end of one): >>>> >>>> ffff8881411f9000 -> ffff8881261c1000 >>>> >>>> ffff8881261c1000 -> ffff88812be26400 >>>> >>>> ffff88812be26400 -> ffff8188392ec000 >>>> >>>> ffff8188392ec000 -> ffff8881a5301000 >>>> >>>> ffff8881a5301000 -> NULL >>>> >>>> which I guess has somehow become detached from its rcache->depot >>>> without being freed properly? However I'm struggling to see any >>>> conceivable way that could happen which wouldn't already be more >>>> severely broken in other ways as well (i.e. either general memory >>>> corruption or someone somehow still trying to use the IOVA domain >>>> while it's being torn down). >>>> >>>> Out of curiosity, does reverting just patch #2 alone make a >>>> difference? And is your workload doing anything "interesting" in >>>> relation to IOVA domain lifetimes, like creating and destroying >>>> SR-IOV virtual functions, changing IOMMU domain types via sysfs, or >>>> using that horrible vdpa thing, or are you seeing this purely from >>>> regular driver DMA API usage? >>> >>> There no lock held when free_iova_rcaches(), is it possible >>> free_iova_rcaches() race with the delayed cancel_delayed_work_sync() ? >>> >>> I don't know why not call cancel_delayed_work_sync(&rcache->work); >>> first in free_iova_rcaches() to avoid possible race. >>> >> between following functions pair, race possible ? if called cocurrently. >> >> 1. free_iova_rcaches() with iova_depot_work_func() >> >>     free_iova_rcaches() holds no lock, iova_depot_work_func() holds >> rcache->lock. > > Unless I've completely misunderstood the workqueue API, that can't > happen, since free_iova_rcaches() *does* synchronously cancel the work > before it starts freeing the depot list. iova_depot_work_func() pop and free mag from depot. free_iova_rcaches() frees loaded and previous mag before syncronously cancelled. different thing. okay here. > >> 2. iova_cpuhp_dead() with iova_depot_work_func() >> >>    iova_cpuhp_dead() holds per cpu lock cpu_rcache->lock, >> iova_depot_work_func() holds rcache->lock. > > That's not a race because those are touching completely different > things - the closest they come to interacting is where they both free > IOVAs back to the rbtree. iova_cpuhp_dead() free pages with iova_magazine_free_pfns(cpu_rcache->loaded, iovad); iova_depot_work_func() free mag from depot. iova_magazine_free_pfns() hold rbtree lock. Okay, different thing. > >> 3. iova_cpuhp_dead() with free_iova_rcaches() >> >>     iova_cpuhp_dead() holds per cpu lock cpu_rcache->lock, >> free_iova_rcaches() holds no lock. > > See iova_domain_free_rcaches() - by the time we call > free_iova_rcaches(), the hotplug handler has already been removed (and > either way it couldn't account for *this* issue since it doesn't touch > the depot at all). Yes, iova_cpuhp_dead() was removed before free_iova_rcaches(). > >> 4. iova_cpuhp_dead() with free_global_cached_iovas() >> >>     iova_cpuhp_dead() holds per cpu lock cpu_rcache->lock and >> free_global_cached_iovas() holds rcache->lock. > > Again, they hold different locks because they're touching unrelated > things. iova_cpuhp_dead() free loaded and previous pages. free_global_cached_iovas() free mags from depot. Okay too. then free_global_cached_iovas() with iova_depot_work_func() ? they all hold rcache->lock. So there is no race at all, perfect.  out of imagination, that memory leak report. kmemleak not always right. Thanks, Ethan > > Thanks, > Robin.