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[194.45.78.10]) by smtp.gmail.com with ESMTPSA id 28-20020a170906225c00b0094ee88207d5sm10921484ejr.191.2023.04.28.03.42.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Apr 2023 03:42:33 -0700 (PDT) From: Jesper Dangaard Brouer X-Google-Original-From: Jesper Dangaard Brouer Message-ID: <4eab92af-251a-a9aa-e270-179634d0345b@redhat.com> Date: Fri, 28 Apr 2023 12:42:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.1 Cc: brouer@redhat.com, lorenzo@kernel.org, linyunsheng@huawei.com, bpf@vger.kernel.org, "David S. Miller" , Jakub Kicinski , Paolo Abeni , Andrew Morton , willy@infradead.org Subject: Re: [PATCH RFC net-next/mm V2 1/2] page_pool: Remove workqueue in new shutdown scheme To: =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= , Ilias Apalodimas , netdev@vger.kernel.org, Eric Dumazet , linux-mm@kvack.org, Mel Gorman References: <168262348084.2036355.16294550378793036683.stgit@firesoul> <168262351129.2036355.1136491155595493268.stgit@firesoul> <871qk582tn.fsf@toke.dk> In-Reply-To: <871qk582tn.fsf@toke.dk> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: CC1E4160016 X-Rspamd-Server: rspam09 X-Stat-Signature: 3z5ux47y71m464jty3p3p55151i6wgce X-HE-Tag: 1682678557-2159 X-HE-Meta: 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 QqPzNEVd un4zbAXSkhDpoZzfh2BNwNJynTlId97lITwtVcUIGfkdIkG+yWAaXJzsRmHxUNspv/tGoloq2YwYRUmIN9W1pDfSoWhGGFPRcMLeyxtC5X8lf8hf+YpyjrOlSXdyClkr9zG43JQZ40kcnJn8ioWK22I0InXQ0hbmGXo2AXpIA2gb1JySmgT6HjylFCRyM0WPqQrb3PD7zYK7TZgpkpa9jlWLJR+BAUSYz3BpkXP9KR6ETYVDUFIj49TFPqDMSOViFA9/2tEACclBhNhIxEg4LcCBbBU5pOmbNQ8o96BEgRWRMpaURTil2jEUNHJHGAsYkKFT9i67ZTKsrtR18VwY1KtQtwz1gnuKGbakoQwikohxiV28kjBbDJm/sDVIEpHxF5LBQzU+wS+ZW35jLq7vBIBplE8LOEldsDjfDD2tG5cYlINGczSTMaPdiY0ziTanG/uY5nHhU1/rxc71J6W/JiYBbh0a4tOWTdvjzFRLfwUdUTsw= 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 27/04/2023 22.53, Toke Høiland-Jørgensen wrote: >> +noinline >> static void page_pool_empty_ring(struct page_pool *pool) >> { >> struct page *page; >> @@ -796,39 +828,29 @@ static void page_pool_scrub(struct page_pool *pool) >> page_pool_empty_ring(pool); >> } > So this is not in the diff context, but page_pool_empty_ring() does > this: > > static void page_pool_empty_ring(struct page_pool *pool) > { > struct page *page; > > /* Empty recycle ring */ > while ((page = ptr_ring_consume_bh(&pool->ring))) { > /* Verify the refcnt invariant of cached pages */ > if (!(page_ref_count(page) == 1)) > pr_crit("%s() page_pool refcnt %d violation\n", > __func__, page_ref_count(page)); > > page_pool_return_page(pool, page); > } > } > > ...and with this patch, that page_pool_return_page() call will now free > the pool memory entirely when the last page is returned. When it does > this, the condition in the while loop will still execute afterwards; it > would return false, but if the pool was freed, it's now referencing > freed memory when trying to read from pool->ring. Yes, that sounds like a problem. > So I think page_pool_empty_ring needs to either pull out all the pages > in the ring to an on-stack buffer before calling page_pool_return_page() > on them, or there needs to be some other way to break the loop early. Let me address this one first, I'll get back to the other in another reply. The usual/idiom way of doing this is to have a next pointer that is populated inside the loop before freeing the object. It should look like this (only compile tested): static void page_pool_empty_ring(struct page_pool *pool) { struct page *page, *next; next = ptr_ring_consume_bh(&pool->ring); /* Empty recycle ring */ while (next) { page = next; next = ptr_ring_consume_bh(&pool->ring); /* Verify the refcnt invariant of cached pages */ if (!(page_ref_count(page) == 1)) pr_crit("%s() page_pool refcnt %d violation\n", __func__, page_ref_count(page)); page_pool_return_page(pool, page); } } > There are a couple of other places where page_pool_return_page() is > called in a loop where the loop variable lives inside struct page_pool, > so we need to be absolutely sure they will never be called in the > shutdown stage, or they'll have to be fixed as well. The other loops are okay, but I spotted another problem in __page_pool_put_page() in "Fallback/non-XDP mode", but that is fixable. --Jesper