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Mon, 20 Jan 2020 14:01:37 +0000 (UTC) Received: from [10.36.118.34] (unknown [10.36.118.34]) by smtp.corp.redhat.com (Postfix) with ESMTP id A164F5C290; Mon, 20 Jan 2020 14:01:36 +0000 (UTC) Subject: Re: [PATCH -mm v2] mm/page_isolation: fix potential warning from user To: Qian Cai Cc: Andrew Morton , mhocko@kernel.org, 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> 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: <74aebdfe-e727-acd6-e664-6e63948a68ae@redhat.com> Date: Mon, 20 Jan 2020 15:01:35 +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: <96675869-3815-4E98-8492-1D84F5B42AED@lca.pw> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 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 14:56, Qian Cai wrote: >=20 >=20 >> On Jan 20, 2020, at 8:38 AM, David Hildenbrand wrot= e: >> >> 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_M= OVABLE) >>>> from start_isolate_page_range(), but should avoid triggering it from >>>> userspace, i.e, from is_mem_section_removable() because it could be = a >>>> DoS if warn_on_panic is set. >>>> >>>> While at it, simplify the code a bit by removing an unnecessary jump >>>> label and a local variable, so set_migratetype_isolate() could reall= y >>>> 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 zone = *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 migratety= pe, int isol_flags) >>>> +static bool set_migratetype_isolate(struct page *page, int migratet= ype, >>>> + 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, make= s >> the function harder to read than before) >=20 > What is Michal or Andrew=E2=80=99s opinion? BTW, a bonus point to retur= n a bool > is that it helps the code robustness in general, as UBSAN will be able = to > catch any abuse. >=20 A return type of bool on a function that does not test a property ("has_...", "is"...") is IMHO confusing. If we have an int, it is clear that "0" means "success". With a bool (true/false), it is not clear. --=20 Thanks, David / dhildenb