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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id 13sm7574112qke.85.2020.01.14.17.38.40 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 14 Jan 2020 17:38:40 -0800 (PST) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 13.0 \(3608.40.2.2.4\)) Subject: Re: [PATCH -next] mm/hotplug: silence a lockdep splat with printk() From: Qian Cai In-Reply-To: <20200114171930.9a0dbd9ae82174abf19b3df5@linux-foundation.org> Date: Tue, 14 Jan 2020 20:38:39 -0500 Cc: Michal Hocko , David Hildenbrand , Sergey Senozhatsky , pmladek@suse.com, rostedt@goodmis.org, peterz@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <8093D190-00C7-43A7-B63E-E06A80D20094@lca.pw> References: <20200114210215.GQ19428@dhcp22.suse.cz> <20200114155339.ad5eee63b9ff38b617ee6168@linux-foundation.org> <20200114171930.9a0dbd9ae82174abf19b3df5@linux-foundation.org> To: Andrew Morton X-Mailer: Apple Mail (2.3608.40.2.2.4) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000006, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > On Jan 14, 2020, at 8:19 PM, Andrew Morton = wrote: >=20 > On Tue, 14 Jan 2020 20:02:31 -0500 Qian Cai wrote: >=20 >>=20 >>=20 >>>> @@ -8290,8 +8290,10 @@ bool has_unmovable_pages(struct zone *zo >>>> return false; >>>> unmovable: >>>> WARN_ON_ONCE(zone_idx(zone) =3D=3D ZONE_MOVABLE); >>>> - if (flags & REPORT_FAILURE) >>>> - dump_page(pfn_to_page(pfn + iter), reason); >>>> + if (flags & REPORT_FAILURE) { >>>> + page =3D pfn_to_page(pfn + iter); >>>=20 >>> This statement appears to be unnecessary. >>=20 >> dump_page() in set_migratetype_isolate() needs that =E2=80=9Cpage=E2=80= =9D. >=20 > local var `page' is never used after this statement. >=20 The goal is to reuse the parameter of has_unmovable_pages((=E2=80=A6, = page, =E2=80=A6) as a return value, so after it returns, dump_page(page, ...) could use = it. I don=E2=80=99t see where it was defined as a local variable. This is probably a bit too hacky, so I=E2=80=99ll change = has_unmovable_pages() to either return "struct page *=E2=80=9D or NULL which is easier to = understand.=