From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) (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 2E7FD111A1 for ; Fri, 23 Aug 2024 01:48:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724377708; cv=none; b=GNWVM0742Izd11w7cP38CU59lY+AHSUOKudsGPu+89WPNX20s9DY9lU3Ocf1nb3QIcD5Ceikb2c0KtyVcaSX+ivyx1zb6d82xkzT8gfd3uEAMLJIO02SoW23dLpL9bcxfvDuHl8V0B+5gAouJIhPWYbkjz1gbbe652vK6h42fHE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724377708; c=relaxed/simple; bh=ulJS3WCxd0O+3BESe7sSlzB3OfiVnjDv+NjQB84lSFE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=vGGk0RPlsJjpUul+laWZU2JJkjeZ7q7uk+RsnEYKC46y99dePAm5Wx98c/bFFkFUZxj3aw8WKiuA6uSwU9Fs6aAW53nYoh+RMBypaGY5X4dbaRo/2G4RGZIH448V+n/2M0C0uuT/wbPdgT6RinvYfEFCNWK18Cw8QyzEs8dQ9qA= 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=BrKD1gz4; arc=none smtp.client-ip=95.215.58.182 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="BrKD1gz4" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1724377703; 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=PPHOSUo6pnc3jr4Qd3Swu3bDszK2Mgq0Ytsd6c+xHpQ=; b=BrKD1gz42LUEASz7L+8rKbtq+XlDFRkk4D1TCgjNBVRPOazJXuHlF7T4pllpd3mout0hoK Xl27UDDvh1dDNkVj6QuzRA+jYafp7d2GpVlgAmkHlTE6yJTHU9xlg9DWWmwelQB0h1+asQ wlTZMZVcxZemHQ89wMSUftvGufZe1NI= Date: Fri, 23 Aug 2024 09:47:52 +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 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> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Hao Ge 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 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 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 >>