From mboxrd@z Thu Jan 1 00:00:00 1970 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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 261CDC07E9D for ; Mon, 26 Sep 2022 13:38:39 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 768098E004E; Mon, 26 Sep 2022 09:38:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 716278E0047; Mon, 26 Sep 2022 09:38:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5B8798E004E; Mon, 26 Sep 2022 09:38:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 48F378E0047 for ; Mon, 26 Sep 2022 09:38:38 -0400 (EDT) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 22CC480BC6 for ; Mon, 26 Sep 2022 13:38:38 +0000 (UTC) X-FDA: 79954341516.04.88ED837 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [193.142.43.52]) by imf23.hostedemail.com (Postfix) with ESMTP id CA919140004 for ; Mon, 26 Sep 2022 13:38:36 +0000 (UTC) Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.92) (envelope-from ) id 1ocoJe-0005aZ-MP; Mon, 26 Sep 2022 15:38:34 +0200 Date: Mon, 26 Sep 2022 15:38:34 +0200 From: Florian Westphal To: Florian Westphal Cc: Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, vbabka@suse.cz, akpm@linux-foundation.org, urezki@gmail.com, netdev@vger.kernel.org, netfilter-devel@vger.kernel.org, Martin Zaharinov Subject: Re: [PATCH mm] mm: fix BUG with kvzalloc+GFP_ATOMIC Message-ID: <20220926133834.GE12777@breakpoint.cc> References: <20220923103858.26729-1-fw@strlen.de> <20220923133512.GE22541@breakpoint.cc> <20220926075639.GA908@breakpoint.cc> <20220926100800.GB12777@breakpoint.cc> <20220926130808.GD12777@breakpoint.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220926130808.GD12777@breakpoint.cc> User-Agent: Mutt/1.10.1 (2018-07-13) ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1664199516; h=from:from:sender: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: in-reply-to:in-reply-to:references:references; bh=2qmqlOACV3glxfZdnBzHWsg8Wgcml3O8PJ4ca+QnXY4=; b=A6c5jazH2roeKj1/T6rrrjOcHkB8S2nD172dSf88fS2Vgune2h+jBt+wNSsltRZEHt0fOn fpAlTFnWu+kfwQl/2hM0i10zIHV73i/XKNAj8TU5hb0Dh3pS1BpmAuaw9+UPnVYfUJxvGS ai1+/W7NMIF72kazwgJfrNZZzyhGpjA= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf23.hostedemail.com: domain of fw@strlen.de designates 193.142.43.52 as permitted sender) smtp.mailfrom=fw@strlen.de ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1664199516; a=rsa-sha256; cv=none; b=hpqL87YGPDRhBxGxYTxBnnY+JKdcwgZDpy2IIK1l5eRyODba/Q78kEZWOt/iqMOR54L2Yu F34uHUspxqMtrNtjfIgicIy9w5e47Dmt3zwF+VRY0fCLuyi8NF0ONNCPf+IEGQniNXzLM5 B79pm/NUQhmhJRjxk6fsyDTc5S3bWv8= X-Rspam-User: X-Rspamd-Queue-Id: CA919140004 X-Rspamd-Server: rspam01 X-Stat-Signature: odunko5etm11zsc7spo76dbjgqrxtznp Authentication-Results: imf23.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf23.hostedemail.com: domain of fw@strlen.de designates 193.142.43.52 as permitted sender) smtp.mailfrom=fw@strlen.de X-HE-Tag: 1664199516-126545 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Florian Westphal wrote: > Michal Hocko wrote: > > On Mon 26-09-22 12:08:00, Florian Westphal wrote: > > > Michal Hocko wrote: > > > > + old_tbl = rht_dereference_rcu(ht->tbl, ht); > > > > + size = tbl->size; > > > > + > > > > + data = ERR_PTR(-EBUSY); > > > > + > > > > + if (rht_grow_above_75(ht, tbl)) > > > > + size *= 2; > > > > + /* Do not schedule more than one rehash */ > > > > + else if (old_tbl != tbl) > > > > + return data; > > > > + > > > > + data = ERR_PTR(-ENOMEM); > > > > + > > > > + rcu_read_unlock(); > > > > + new_tbl = bucket_table_alloc(ht, size, GFP_KERNEL); > > > > + rcu_read_lock(); > > > > > > I don't think this is going to work, there can be callers that > > > rely on rcu protected data structures getting free'd. > > > > The caller of this function drops RCU for each retry, why should be the > > called function any special? > > I was unfortunately never able to fully understand rhashtable. Obviously. > AFAICS the rcu_read_lock/unlock in the caller is pointless, > or at least dubious. Addedum, I can't read: void *rhashtable_insert_slow(struct rhashtable *ht, const void *key, struct rhash_head *obj) { void *data; do { rcu_read_lock(); data = rhashtable_try_insert(ht, key, obj); rcu_read_unlock(); } } while (PTR_ERR(data) == -EAGAIN); } ... which is needed to prevent a lockdep splat in rhashtable_try_insert() -- there is no guarantee the caller already has rcu_read_lock(). > To the best of my knowledge there are users of this interface that > invoke it with rcu read lock held, and since those always nest, the > rcu_read_unlock() won't move us to GFP_KERNEL territory. > > I guess you can add a might_sleep() and ask kernel to barf at runtime. I did and it triggers. Caller is inet_frag_find(), triggered via 'ping -s 60000 $addr'.