From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) (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 097341EF1D for ; Fri, 23 Aug 2024 03:37:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724384235; cv=none; b=AHhOJ93k9zD9e524T7Ru/S/Z4qUcpSMyhoMsYNA2A9dtQxhXbr+vPhf9LgtQkdA2UbkSw5got/0p4Z672424DDDRYofmJE5Cz88BcW6xPypufrp3TG+3TFeZcKHpU+zYFRfDX050YocGwIOeatdfWGb6KYBQ7pgD9IONc7uA5vU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724384235; c=relaxed/simple; bh=Z8QEmwIvhhBAtgzzjvQ1Vyn70bF/wzXSmXShbJdc3JE=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=apc1GmVkbxoP+WDM8Zh6lCh8oA108c3GbcS2l1F0MugfZfOKAe8USEzGhVL95Iw5XkOFbPB5N7vRggzSWzDX1qyJvTg4E6lcU3OalwBAUPPka5yQJHI7OtN82kTVQbOecvvmbMekqW2WgMoGuqyDzo7gDkX+Y0J3Q6ZEj2D53MU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=NZoC87Hz; arc=none smtp.client-ip=91.218.175.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="NZoC87Hz" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1724384230; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=cY24nOUEo2m206GlJwgB19ZAs8hLikNfAgK8dR8ZU44=; b=NZoC87Hz1pLFaHnHL4SbGQcF+e9d+YA3JSgICauOGv4UM+ANdhV6hrDti2FSSQWlFQHHI6 c5oYcYwk8maD7LYJA5HR5HIDwJvhINjWA+Jd6WOSKCK5UYkz1po8/AKORUJOl7mKDDurI0 ypYUPtj+ZIRRLA9eRWb5JTkvEgBI0MA= Date: Fri, 23 Aug 2024 11:37:05 +0800 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH] codetag: debug: mark codetags for pages which transitioned from being poison to unpoison as empty X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Hao Ge To: Suren Baghdasaryan , Miaohe Lin Cc: kent.overstreet@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hao Ge , stable@vger.kernel.org, nao.horiguchi@gmail.com, akpm@linux-foundation.org, pasha.tatashin@soleen.com, david@redhat.com References: <20240822025800.13380-1-hao.ge@linux.dev> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Hi Suren and Miaohe On 8/23/24 09:47, Hao Ge wrote: > Hi Suren and Miaohe > > > Thank you all for taking the time to discuss this issue. > > > On 8/23/24 06:50, Suren Baghdasaryan wrote: >> On Thu, Aug 22, 2024 at 2:46 AM Hao Ge wrote: >>> Hi Miaohe >>> >>> >>> Thank you for taking the time to review this patch. >>> >>> >>> On 8/22/24 16:04, Miaohe Lin wrote: >>>> On 2024/8/22 10:58, Hao Ge wrote: >>>>> From: Hao Ge >>>>> >>>> Thanks for your patch. >>>> >>>>> The PG_hwpoison page will be caught and isolated on the entrance to >>>>> the free buddy page pool. so,when we clear this flag and return it >>>>> to the buddy system,mark codetags for pages as empty. >>>>> >>>> Is below scene cause the problem? >>>> >>>> 1. Pages are allocated. pgalloc_tag_add() will be called when >>>> prep_new_page(). >>>> >>>> 2. Pages are hwpoisoned. memory_failure() will set PG_hwpoison flag >>>> and pgalloc_tag_sub() >>>> will be called when pages are caught and isolated on the entrance >>>> to buddy. >> Hi Folks, >> Thanks for reporting this! Could you please describe in more details >> how memory_failure() ends up calling pgalloc_tag_sub()? It's not >> obvious to me which path leads to pgalloc_tag_sub(), so I must be >> missing something. > > > OK,Let me describe the scenario I encountered. > > In the Link [1] I mentioned,here is the logic behind it: > > It performed the following operations: > > madvise(ptrs[num_alloc], pagesize, MADV_SOFT_OFFLINE) > > and then the kernel's call stack looks like this: > > do_madvise > > soft_offline_page > > page_handle_poison > > __folio_put > > free_unref_page > I just reviewed it and I think I missed a stack. Actually, it's like this do_madvise soft_offline_page soft_offline_in_use_page page_handle_poison __folio_put free_unref_page And I've come up with a minimal solution. If everyone agrees, I'll send the patch.look this https://elixir.bootlin.com/linux/v6.11-rc4/source/mm/page_alloc.c#L1056 Let's directly call clear_page_tag_ref after pgalloc_tag_sub. Thanks BR Hao > It will set a flag within the following function and then release the > page. > > https://elixir.bootlin.com/linux/v6.11-rc4/source/mm/memory-failure.c#L206 > > > and and then,because you set the PG_hwpoison flag, so the page will be > caught and isolated on the > > entrance to the free buddy page pool. look here: > > https://elixir.bootlin.com/linux/v6.11-rc4/source/mm/page_alloc.c#L1052 > > At this very moment, we call pgalloc_tag_sub. > > So,when we callunpoison_memoryclear this flag and return the page to > the buddy system, the problem arises. > > >> On a conceptual level I want to understand if the page isolated in >> this manner should be considered freed or not. If it shouldn't be >> considered free then I think the right fix would be to avoid >> pgalloc_tag_sub() when this isolation happens. >> Thanks, >> Suren. > > In my understanding, the purpose of unpoison_memory is to reclaim > poisoned pages. > > I dug up the patch that introduced this function back then > > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/mm/memory-failure.c?id=847ce401df392b0704369fd3f75df614ac1414b4 > > > Therefore, this is reasonable. > > Thanks > > Best regards > > Hao > >> >>>> 3. unpoison_memory cleared flags and sent the pages to buddy. >>>> pgalloc_tag_sub() will be >>>> called again in free_pages_prepare(). >>>> >>>> So there is a imbalance that pgalloc_tag_add() is called once and >>>> pgalloc_tag_sub() is called twice? >>> As you said, that's exactly the case. >>>> If so, let's think about more complicated scene: >>>> >>>> 1. Same as above. >>>> >>>> 2. Pages are hwpoisoned. But memory_failure() fails to handle it. >>>> So PG_hwpoison flag is set >>>> but pgalloc_tag_sub() is not called (pages are not sent to buddy). >>>> >>>> 3. unpoison_memory cleared flags and calls clear_page_tag_ref() >>>> without calling pgalloc_tag_sub() >>>> first. Will this cause problem? >>>> >>>> Though this should be really rare... >>>> >>>> Thanks. >>>> . >>> Great, I didn't anticipate this scenario. >>> >>> When we call clear_page_tag_ref() without calling pgalloc_tag_sub(), >>> >>> It will cause exceptions >>> in|tag->counters->bytes|and|tag->counters->calls|. >>> >>> We can add a layer of protection to handle it >>> >>> The pseudocode is as follows: >>> >>> if (mem_alloc_profiling_enabled()) { >>>           union codetag_ref *ref = get_page_tag_ref(page); >>> >>>           if (ref) { >>>               if( ref->ct != NULL && !is_codetag_empty(ref)) >>>               { >>>                   tag = ct_to_alloc_tag(ref->ct); >>>                   this_cpu_sub(tag->counters->bytes, bytes); >>>                   this_cpu_dec(tag->counters->calls); >>>               } >>>               set_codetag_empty(ref); >>>               put_page_tag_ref(ref); >>>           } >>> } >>> >>> Hi Suren and Kent >>> >>> Do you have any suggestions for this? If it's okay, I'll add comments >>> and include this pseudocode in|clear_page_tag_ref|. >>> >>>>> It was detected by [1] and the following WARN occurred: >>>>> >>>>> [  113.930443][ T3282] ------------[ cut here ]------------ >>>>> [  113.931105][ T3282] alloc_tag was not set >>>>> [  113.931576][ T3282] WARNING: CPU: 2 PID: 3282 at >>>>> ./include/linux/alloc_tag.h:130 pgalloc_tag_sub.part.66+0x154/0x164 >>>>> [  113.932866][ T3282] Modules linked in: hwpoison_inject fuse >>>>> ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 >>>>> xt_conntrack ebtable_nat ebtable_broute ip6table_nat ip6table_man4 >>>>> [  113.941638][ T3282] CPU: 2 UID: 0 PID: 3282 Comm: madvise11 >>>>> Kdump: loaded Tainted: G        W 6.11.0-rc4-dirty #18 >>>>> [  113.943003][ T3282] Tainted: [W]=WARN >>>>> [  113.943453][ T3282] Hardware name: QEMU KVM Virtual Machine, >>>>> BIOS unknown 2/2/2022 >>>>> [  113.944378][ T3282] pstate: 40400005 (nZcv daif +PAN -UAO -TCO >>>>> -DIT -SSBS BTYPE=--) >>>>> [  113.945319][ T3282] pc : pgalloc_tag_sub.part.66+0x154/0x164 >>>>> [  113.946016][ T3282] lr : pgalloc_tag_sub.part.66+0x154/0x164 >>>>> [  113.946706][ T3282] sp : ffff800087093a10 >>>>> [  113.947197][ T3282] x29: ffff800087093a10 x28: ffff0000d7a9d400 >>>>> x27: ffff80008249f0a0 >>>>> [  113.948165][ T3282] x26: 0000000000000000 x25: ffff80008249f2b0 >>>>> x24: 0000000000000000 >>>>> [  113.949134][ T3282] x23: 0000000000000001 x22: 0000000000000001 >>>>> x21: 0000000000000000 >>>>> [  113.950597][ T3282] x20: ffff0000c08fcad8 x19: ffff80008251e000 >>>>> x18: ffffffffffffffff >>>>> [  113.952207][ T3282] x17: 0000000000000000 x16: 0000000000000000 >>>>> x15: ffff800081746210 >>>>> [  113.953161][ T3282] x14: 0000000000000000 x13: 205d323832335420 >>>>> x12: 5b5d353031313339 >>>>> [  113.954120][ T3282] x11: ffff800087093500 x10: 000000000000005d >>>>> x9 : 00000000ffffffd0 >>>>> [  113.955078][ T3282] x8 : 7f7f7f7f7f7f7f7f x7 : ffff80008236ba90 >>>>> x6 : c0000000ffff7fff >>>>> [  113.956036][ T3282] x5 : ffff000b34bf4dc8 x4 : ffff8000820aba90 >>>>> x3 : 0000000000000001 >>>>> [  113.956994][ T3282] x2 : ffff800ab320f000 x1 : 841d1e35ac932e00 >>>>> x0 : 0000000000000000 >>>>> [  113.957962][ T3282] Call trace: >>>>> [  113.958350][ T3282] pgalloc_tag_sub.part.66+0x154/0x164 >>>>> [  113.959000][ T3282]  pgalloc_tag_sub+0x14/0x1c >>>>> [  113.959539][ T3282]  free_unref_page+0xf4/0x4b8 >>>>> [  113.960096][ T3282]  __folio_put+0xd4/0x120 >>>>> [  113.960614][ T3282]  folio_put+0x24/0x50 >>>>> [  113.961103][ T3282]  unpoison_memory+0x4f0/0x5b0 >>>>> [  113.961678][ T3282]  hwpoison_unpoison+0x30/0x48 [hwpoison_inject] >>>>> [  113.962436][ T3282] simple_attr_write_xsigned.isra.34+0xec/0x1cc >>>>> [  113.963183][ T3282]  simple_attr_write+0x38/0x48 >>>>> [  113.963750][ T3282]  debugfs_attr_write+0x54/0x80 >>>>> [  113.964330][ T3282]  full_proxy_write+0x68/0x98 >>>>> [  113.964880][ T3282]  vfs_write+0xdc/0x4d0 >>>>> [  113.965372][ T3282]  ksys_write+0x78/0x100 >>>>> [  113.965875][ T3282]  __arm64_sys_write+0x24/0x30 >>>>> [  113.966440][ T3282]  invoke_syscall+0x7c/0x104 >>>>> [  113.966984][ T3282] el0_svc_common.constprop.1+0x88/0x104 >>>>> [  113.967652][ T3282]  do_el0_svc+0x2c/0x38 >>>>> [  113.968893][ T3282]  el0_svc+0x3c/0x1b8 >>>>> [  113.969379][ T3282]  el0t_64_sync_handler+0x98/0xbc >>>>> [  113.969980][ T3282]  el0t_64_sync+0x19c/0x1a0 >>>>> [  113.970511][ T3282] ---[ end trace 0000000000000000 ]--- >>>>> >>>>> Link [1]: >>>>> https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/madvise/madvise11.c >>>>> >>>>> Fixes: a8fc28dad6d5 ("alloc_tag: introduce clear_page_tag_ref() >>>>> helper function") >>>>> Cc: stable@vger.kernel.org # v6.10 >>>>> Signed-off-by: Hao Ge >>>>> --- >>>>>    mm/memory-failure.c | 6 ++++++ >>>>>    1 file changed, 6 insertions(+) >>>>> >>>>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >>>>> index 7066fc84f351..570388c41532 100644 >>>>> --- a/mm/memory-failure.c >>>>> +++ b/mm/memory-failure.c >>>>> @@ -2623,6 +2623,12 @@ int unpoison_memory(unsigned long pfn) >>>>> >>>>>               folio_put(folio); >>>>>               if (TestClearPageHWPoison(p)) { >>>>> +                    /* the PG_hwpoison page will be caught and >>>>> isolated >>>>> +                     * on the entrance to the free buddy page pool. >>>>> +                     * so,when we clear this flag and return it >>>>> to the buddy system, >>>>> +                     * clear it's codetag >>>>> +                     */ >>>>> +                    clear_page_tag_ref(p); >>>>>                       folio_put(folio); >>>>>                       ret = 0; >>>>>               } >>>>> >>>>> >>> Thanks >>> >>> BR >>> >>> Hao >>>