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bh=5XeMF8jQzp3Dp3pYeKgR8FPosfe763x1qsXohvbYslA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=rcgrwrft7kR4eHoesRwq0phMWCnKTm9rS2/Q5S9ax9cmVT0Uteeux58qylmfFQwG9 RhucOsKTfBCuWRMeAS2pFqSLqRHlsbDLtRTWcskLexY7wzNZQQPd+Bc0lt9eBE8k0k N3jlCcZTltPkwNP2L0lxsFa+j5lUdv2Q3G/jZovY= Date: Mon, 13 Mar 2023 12:31:02 -0700 From: Andrew Morton To: Mike Kravetz Cc: Baolin Wang , mgorman@techsingularity.net, osalvador@suse.de, vbabka@suse.cz, william.lam@bytedance.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] mm: compaction: fix the possible deadlock when isolating hugetlb pages Message-Id: <20230313123102.52118e6007f21c45063fbe79@linux-foundation.org> In-Reply-To: <20230313170838.GA3044@monkey> References: <1bc1c955b03603c4e14f56dfbbef9f637f18dbbd.1678703534.git.baolin.wang@linux.alibaba.com> <20230313170838.GA3044@monkey> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: D4CA24001B X-Stat-Signature: 41x19u7kwa17f8xare7mmx1j54wrejjc X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1678735866-86293 X-HE-Meta: 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 nazdAnvb QGyYS5pKD0FPWtF0kOCDHmMkQ2g715kHXaZ3BuhMlGiWJk97pvcR7/ItsYPJwOi0pxPfgEmziLoxkPacPFzZOfEQUCbE9i+6uxipzMS2Gf/oq/fEatM4G3qeBK4wz5VlZmDX9hVW4p9Z+wv9DcUQvtONXT+feyAQp95o19dYQV/qGY7iM1hJeJOgVpZvWdl37bu1UA6LsKVkwocshhUEVOaKxID/7mwGDGVt8AjEXsWWKN6tojtBKA9nG5rJzmffWwqqkGXJWYNbP6L9OTt0aZJcjweoITDRYn5BJUlZVzx2tVM/cH1WhQHsz0ID/2JsG8a+XZLyn80EhrKc8h9IOk+LzWppQCiP6L2+vxKzqXq+kk7Q/TuFGXwBN8w== 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, 13 Mar 2023 10:08:38 -0700 Mike Kravetz wrote: > I suspect holding the lru lock when calling isolate_or_dissolve_huge_page was > not considered. However, I wonder if this can really happen in practice? > > Before the code below, there is this: > > /* > * Periodically drop the lock (if held) regardless of its > * contention, to give chance to IRQs. Abort completely if > * a fatal signal is pending. > */ > if (!(low_pfn % COMPACT_CLUSTER_MAX)) { > if (locked) { > unlock_page_lruvec_irqrestore(locked, flags); > locked = NULL; > } > ... > } > > It would seem that the pfn of a hugetlb page would always be a multiple of > COMPACT_CLUSTER_MAX so we would drop the lock. However, I am not sure if > that is ALWAYS true and would prefer something like the code you suggested. > > Did you actually see this deadlock in practice? Presumably the lack of lockdep reports about this tells us something?