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Mon, 26 Sep 2022 12:02:18 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id E1C5D8qUMWM5RAAAMHmgww (envelope-from ); Mon, 26 Sep 2022 12:02:18 +0000 Date: Mon, 26 Sep 2022 14:02:17 +0200 From: Michal Hocko To: Florian Westphal Cc: 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: References: <20220923103858.26729-1-fw@strlen.de> <20220923133512.GE22541@breakpoint.cc> <20220926075639.GA908@breakpoint.cc> <20220926100800.GB12777@breakpoint.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220926100800.GB12777@breakpoint.cc> ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=teQ+cile; spf=pass (imf08.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com; 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dmarc=pass (policy=quarantine) header.from=suse.com X-Stat-Signature: xcy1y7tomcy79x17i1n85zjhhdutbihz X-Rspamd-Queue-Id: C3122160011 X-Rspamd-Server: rspam12 X-Rspam-User: X-HE-Tag: 1664193739-283774 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: 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? -- Michal Hocko SUSE Labs