From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 C6A9280C13 for ; Thu, 8 Aug 2024 18:32:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723141964; cv=none; b=Cz+3s5ebTY1BMjBMSk+o1Gbs/LI/l64YVgI1lLNHvObthM0VtUSVBjubsKFzLOzzxrkMxKbYoAchxhVftqffSEtGx2puzdRvPzA0yCYazPFR/MkFYEyFoyVAsOqbytW3JgYvhRqK6+C0YlRwvROEU1HlbknnWB3L6mmhw3VZ3w0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723141964; c=relaxed/simple; bh=m4Ld8dHbB+JXQotUzhSuM6EmaklWFfNmYOEsUH6d9Pg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=SXR/DhQcaqstTzvhnuMfShpyZZDveB8IW80QQbROQPZlw47ZMi1tS6Whx21MjuMp27vJP7aUjqAcBzI16VBYaqGZL7UphGokMS+pferDFBxug3nTkDxm3j3cnNe1pMmXmApKqN4KeB2MYdeDTxebvIcDttWe7g03flJLDEvGDuk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=hc09FZTP; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="hc09FZTP" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1723141960; 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=smsHi6xEMXRFi8V3HreFHnPllEpbGv3MaP8Bg03pLpM=; b=hc09FZTPPAPQj8AChOdn0erSw0b2owbMQxiOgK4kb2A/k9S7qlavDCKcAlIkOrz5NNrpzn jdZzOtU+Kopk9Nyz8pdgIPQnnEm6gMrSxvcA544XAABbS7mK4XwWD6SY/fIORJJR3cVaqm hpI7H04DK9F99b0NDo4Gbupc7Jn9qlU= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-616-qTL7JnWaOM6bx3Z9eRmUZw-1; Thu, 08 Aug 2024 14:32:35 -0400 X-MC-Unique: qTL7JnWaOM6bx3Z9eRmUZw-1 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CCB381944A86; Thu, 8 Aug 2024 18:32:33 +0000 (UTC) Received: from [10.2.16.232] (unknown [10.2.16.232]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 64E8719560AA; Thu, 8 Aug 2024 18:32:32 +0000 (UTC) Message-ID: Date: Thu, 8 Aug 2024 14:32:31 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] lib/stackdepot: Double DEPOT_POOLS_CAP if KASAN is enabled To: Andrey Konovalov Cc: Andrew Morton , Andrey Ryabinin , Marco Elver , Dmitry Vyukov , linux-kernel@vger.kernel.org References: <20240808125430.1172152-1-longman@redhat.com> Content-Language: en-US From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 On 8/8/24 12:12, Andrey Konovalov wrote: > On Thu, Aug 8, 2024 at 2:54 PM Waiman Long wrote: >> As said in commit 02754e0a484a ("lib/stackdepot.c: bump stackdepot >> capacity from 16MB to 128MB"), KASAN uses stackdepot to memorize stacks >> for all kmalloc/kfree calls. So stackdepot capacity was increased 8 >> times to accommodate KASAN usage even thought it was claimed 4X should >> be enough at that time. >> >> With commit fc60e0caa94d ("lib/stackdepot: use fixed-sized slots >> for stack records"), all stackdepot records uses a fixed size with >> CONFIG_STACKDEPOT_MAX_FRAMES (default=64) entries. This is merged to >> support evictable KASAN stack records. Commit 31639fd6cebd ("stackdepot: >> use variable size records for non-evictable entries") re-enabled >> the use of variable size records for non-KASAN use cases, but KASAN >> (generic mode) still uses the large fixed size stack records. > No, since commit 711d349174fd ("kasan: revert eviction of stack traces > in generic mode") Generic KASAN doesn't use fixed-sized slots. > >> With the default CONFIG_STACKDEPOT_MAX_FRAMES of 64, KASAN use of >> stackdepot space had been more than double than before. Assuming an >> average stack frame size of 16, a KASAN stack record is almost 4X the >> size of a non-KASAN one. > So this is not correct. Yes, you are right. I missed the KASAN commit 711d349174fd in my analysis. I will update the commit log in the next version. >> When a wide variety of workloads are run on a debug kernel with KASAN >> enabled, the following warning may sometimes be printed. >> >> [ 6818.650674] Stack depot reached limit capacity >> [ 6818.650730] WARNING: CPU: 1 PID: 272741 at lib/stackdepot.c:252 depot_alloc_stack+0x39e/0x3d0 >> : >> [ 6818.650907] Call Trace: >> [ 6818.650909] [<00047dd453d84b92>] depot_alloc_stack+0x3a2/0x3d0 >> [ 6818.650916] [<00047dd453d85254>] stack_depot_save_flags+0x4f4/0x5c0 >> [ 6818.650920] [<00047dd4535872c6>] kasan_save_stack+0x56/0x70 >> [ 6818.650924] [<00047dd453587328>] kasan_save_track+0x28/0x40 >> [ 6818.650927] [<00047dd45358a27a>] kasan_save_free_info+0x4a/0x70 >> [ 6818.650930] [<00047dd45358766a>] __kasan_slab_free+0x12a/0x1d0 >> [ 6818.650933] [<00047dd45350deb4>] kmem_cache_free+0x1b4/0x580 >> [ 6818.650938] [<00047dd452c520da>] __put_task_struct+0x24a/0x320 >> [ 6818.650945] [<00047dd452c6aee4>] delayed_put_task_struct+0x294/0x350 >> [ 6818.650949] [<00047dd452e9066a>] rcu_do_batch+0x6ea/0x2090 >> [ 6818.650953] [<00047dd452ea60f4>] rcu_core+0x474/0xa90 >> [ 6818.650956] [<00047dd452c780c0>] handle_softirqs+0x3c0/0xf90 >> [ 6818.650960] [<00047dd452c76fbe>] __irq_exit_rcu+0x35e/0x460 >> [ 6818.650963] [<00047dd452c79992>] irq_exit_rcu+0x22/0xb0 >> [ 6818.650966] [<00047dd454bd8128>] do_ext_irq+0xd8/0x120 >> [ 6818.650972] [<00047dd454c0ddd0>] ext_int_handler+0xb8/0xe8 >> [ 6818.650979] [<00047dd453589cf6>] kasan_check_range+0x236/0x2f0 >> [ 6818.650982] [<00047dd453378cf0>] filemap_get_pages+0x190/0xaa0 >> [ 6818.650986] [<00047dd453379940>] filemap_read+0x340/0xa70 >> [ 6818.650989] [<00047dd3d325d226>] xfs_file_buffered_read+0x2c6/0x400 [xfs] >> [ 6818.651431] [<00047dd3d325dfe2>] xfs_file_read_iter+0x2c2/0x550 [xfs] >> [ 6818.651663] [<00047dd45364710c>] vfs_read+0x64c/0x8c0 >> [ 6818.651669] [<00047dd453648ed8>] ksys_read+0x118/0x200 >> [ 6818.651672] [<00047dd452b6cf5a>] do_syscall+0x27a/0x380 >> [ 6818.651676] [<00047dd454bd7e74>] __do_syscall+0xf4/0x1a0 >> [ 6818.651680] [<00047dd454c0db58>] system_call+0x70/0x98 >> >> With all the recent changes in stackdepot to support new KASAN features, >> it is obvious that the current DEPOT_POOLS_CAP of 8192 may not be >> enough when KASAN is enabled. Fix this stackdepot capability issue >> by doubling DEPOT_POOLS_CAP if KASAN is enabled. With 4k pages, the >> maximum stackdepot capacity is doubled to 256 MB with KASAN enabled. > It is possible that the stack depot runs out of space due to a truly > large number of unique stack traces, but I would first make sure that > is indeed the case. The one thing to check would be to dump all the > stack traces from the stack depot when it overflows, and check whether > they make sense. There have been cases in the past, when e.g. the task > context part of a stack trace from an interrupt didn't get stripped > properly, and thus almost each stack trace from an interrupt was > considered unique by the stack depot. Perhaps, something similar > started happening again. It could be. Anyway, I got a bug report from our QE team and they have seen it once so far. So it is not an easily reproducible problem. I need to do further investigation first. Thanks for your quick response. Cheers, Longman