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Mon, 20 Jan 2020 14:13:56 +0000 (UTC) Received: from [10.36.118.34] (unknown [10.36.118.34]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7CC6610027A3; Mon, 20 Jan 2020 14:13:55 +0000 (UTC) Subject: Re: [PATCH -mm v2] mm/page_isolation: fix potential warning from user To: Qian Cai Cc: Andrew Morton , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20200120131909.813-1-cai@lca.pw> <8c56268d-9b8a-f62e-eca9-7707852a2aaf@redhat.com> <96675869-3815-4E98-8492-1D84F5B42AED@lca.pw> <74aebdfe-e727-acd6-e664-6e63948a68ae@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: Date: Mon, 20 Jan 2020 15:13:54 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Content-Transfer-Encoding: quoted-printable 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 20.01.20 15:11, Qian Cai wrote: >=20 >=20 >> On Jan 20, 2020, at 9:01 AM, David Hildenbrand wrot= e: >> >> On 20.01.20 14:56, Qian Cai wrote: >>> >>> >>>> On Jan 20, 2020, at 8:38 AM, David Hildenbrand wr= ote: >>>> >>>> On 20.01.20 14:30, David Hildenbrand wrote: >>>>> On 20.01.20 14:19, Qian Cai wrote: >>>>>> It makes sense to call the WARN_ON_ONCE(zone_idx(zone) =3D=3D ZONE= _MOVABLE) >>>>>> from start_isolate_page_range(), but should avoid triggering it fr= om >>>>>> userspace, i.e, from is_mem_section_removable() because it could b= e a >>>>>> DoS if warn_on_panic is set. >>>>>> >>>>>> While at it, simplify the code a bit by removing an unnecessary ju= mp >>>>>> label and a local variable, so set_migratetype_isolate() could rea= lly >>>>>> return a bool. >>>>>> >>>>>> Suggested-by: Michal Hocko >>>>>> Signed-off-by: Qian Cai >>>>>> --- >>>>>> >>>>>> v2: Improve the commit log. >>>>>> Warn for all start_isolate_page_range() users not just offlining= . >>>>>> >>>>>> mm/page_alloc.c | 11 ++++------- >>>>>> mm/page_isolation.c | 30 +++++++++++++++++------------- >>>>>> 2 files changed, 21 insertions(+), 20 deletions(-) >>>>>> >>>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>>>>> index 621716a25639..3c4eb750a199 100644 >>>>>> --- a/mm/page_alloc.c >>>>>> +++ b/mm/page_alloc.c >>>>>> @@ -8231,7 +8231,7 @@ struct page *has_unmovable_pages(struct zone= *zone, struct page *page, >>>>>> if (is_migrate_cma(migratetype)) >>>>>> return NULL; >>>>>> >>>>>> - goto unmovable; >>>>>> + return page; >>>>>> } >>>>>> >>>>>> for (; iter < pageblock_nr_pages; iter++) { >>>>>> @@ -8241,7 +8241,7 @@ struct page *has_unmovable_pages(struct zone= *zone, struct page *page, >>>>>> page =3D pfn_to_page(pfn + iter); >>>>>> >>>>>> if (PageReserved(page)) >>>>>> - goto unmovable; >>>>>> + return page; >>>>>> >>>>>> /* >>>>>> * If the zone is movable and we have ruled out all reserved >>>>>> @@ -8261,7 +8261,7 @@ struct page *has_unmovable_pages(struct zone= *zone, struct page *page, >>>>>> unsigned int skip_pages; >>>>>> >>>>>> if (!hugepage_migration_supported(page_hstate(head))) >>>>>> - goto unmovable; >>>>>> + return page; >>>>>> >>>>>> skip_pages =3D compound_nr(head) - (page - head); >>>>>> iter +=3D skip_pages - 1; >>>>>> @@ -8303,12 +8303,9 @@ struct page *has_unmovable_pages(struct zon= e *zone, struct page *page, >>>>>> * is set to both of a memory hole page and a _used_ kernel >>>>>> * page at boot. >>>>>> */ >>>>>> - goto unmovable; >>>>>> + return page; >>>>>> } >>>>>> return NULL; >>>>>> -unmovable: >>>>>> - WARN_ON_ONCE(zone_idx(zone) =3D=3D ZONE_MOVABLE); >>>>>> - return pfn_to_page(pfn + iter); >>>>>> } >>>>>> >>>>>> #ifdef CONFIG_CONTIG_ALLOC >>>>>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c >>>>>> index e70586523ca3..31f5516f5d54 100644 >>>>>> --- a/mm/page_isolation.c >>>>>> +++ b/mm/page_isolation.c >>>>>> @@ -15,12 +15,12 @@ >>>>>> #define CREATE_TRACE_POINTS >>>>>> #include >>>>>> >>>>>> -static int set_migratetype_isolate(struct page *page, int migrate= type, int isol_flags) >>>>>> +static bool set_migratetype_isolate(struct page *page, int migrat= etype, >>>>>> + int isol_flags) >>>>> >>>>> Why this change? >>>>> >>>>>> { >>>>>> - struct page *unmovable =3D NULL; >>>>>> + struct page *unmovable =3D ERR_PTR(-EBUSY); >>>>> >>>>> Also, why this change? >>>>> >>>>>> struct zone *zone; >>>>>> unsigned long flags; >>>>>> - int ret =3D -EBUSY; >>>>>> >>>>>> zone =3D page_zone(page); >>>>>> >>>>>> @@ -49,21 +49,25 @@ static int set_migratetype_isolate(struct page= *page, int migratetype, int isol_ >>>>>> NULL); >>>>>> >>>>>> __mod_zone_freepage_state(zone, -nr_pages, mt); >>>>>> - ret =3D 0; >>>>>> } >>>>>> >>>>>> out: >>>>>> spin_unlock_irqrestore(&zone->lock, flags); >>>>>> - if (!ret) >>>>>> + >>>>>> + if (!unmovable) { >>>>>> drain_all_pages(zone); >>>>>> - else if ((isol_flags & REPORT_FAILURE) && unmovable) >>>>>> - /* >>>>>> - * printk() with zone->lock held will guarantee to trigger a >>>>>> - * lockdep splat, so defer it here. >>>>>> - */ >>>>>> - dump_page(unmovable, "unmovable page"); >>>>>> - >>>>>> - return ret; >>>>>> + } else { >>>>>> + WARN_ON_ONCE(zone_idx(zone) =3D=3D ZONE_MOVABLE); >>>>>> + >>>>>> + if ((isol_flags & REPORT_FAILURE) && !IS_ERR(unmovable)) >>>>>> + /* >>>>> >>>>> Why this change? (!IS_ERR) >>>>> >>>>> >>>>> Some things here look unrelated - or I am missing something :) >>>>> >>>> >>>> FWIW, I'd prefer this change without any such cleanups (e.g., I don'= t >>>> like returning a bool from this function and the IS_ERR handling, ma= kes >>>> the function harder to read than before) >>> >>> What is Michal or Andrew=E2=80=99s opinion? BTW, a bonus point to ret= urn a bool >>> is that it helps the code robustness in general, as UBSAN will be abl= e to >>> catch any abuse. >>> >> >> A return type of bool on a function that does not test a property >> ("has_...", "is"...") is IMHO confusing. >=20 > That is fine. It could be renamed to set_migratetype_is_isolate() or > is_set_migratetype_isolate() which seems pretty minor because we > have no consistency in the naming of this in linux kernel at all, i.e., > many existing bool function names without those test of properties.=20 It does not query a property, so "is_set_migratetype_isolate()" is plain wrong. Anyhow, Michal does not seem to care. --=20 Thanks, David / dhildenb