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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id q49sm10571235qta.60.2019.10.07.05.11.45 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 07 Oct 2019 05:11:45 -0700 (PDT) Message-ID: <1570450304.5576.283.camel@lca.pw> Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk() From: Qian Cai To: Michal Hocko Cc: akpm@linux-foundation.org, sergey.senozhatsky.work@gmail.com, pmladek@suse.com, rostedt@goodmis.org, peterz@infradead.org, david@redhat.com, john.ogness@linutronix.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org Date: Mon, 07 Oct 2019 08:11:44 -0400 In-Reply-To: <20191007113710.GH2381@dhcp22.suse.cz> References: <20191007080742.GD2381@dhcp22.suse.cz> <20191007113710.GH2381@dhcp22.suse.cz> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-10.el7) Mime-Version: 1.0 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 Mon, 2019-10-07 at 13:37 +0200, Michal Hocko wrote: > On Mon 07-10-19 07:04:00, Qian Cai wrote: > >=20 > >=20 > > > On Oct 7, 2019, at 4:07 AM, Michal Hocko wrote: > > >=20 > > > I do not think that removing the printk is the right long term solu= tion. > > > While I do agree that removing the debugging printk __offline_isola= ted_pages > > > does make sense because it is essentially of a very limited use, th= is > > > doesn't really solve the underlying problem. There are likely othe= r > > > printks from zone->lock. It would be much more saner to actually > > > disallow consoles to allocate any memory while printk is called fro= m an > > > atomic context. > >=20 > > No, there is only a handful of places called printk() from > > zone->lock. It is normal that the callers will quietly process > > =E2=80=9Cstruct zone=E2=80=9D modification in a short section with zo= ne->lock > > held. >=20 > It is extremely error prone to have any zone->lock vs. printk > dependency. I do not want to play an endless whack a mole. >=20 > > No, it is not about =E2=80=9Callocate any memory while printk is call= ed from an > > atomic context=E2=80=9D. It is opposite lock chain from different pr= ocessors which has the same effect. For example, > >=20 > > CPU0: CPU1: CPU2: > > console_owner > > sclp_lock > > sclp_lock zone_lock > > zone_lock > > console_owner >=20 > Why would sclp_lock ever take a zone->lock (apart from an allocation). > So really if sclp_lock is a lock that might be taken from many contexts > and generate very subtle lock dependencies then it should better be > really careful what it is calling into. >=20 > In other words you are trying to fix a wrong end of the problem. Fix th= e > console to not allocate or depend on MM by other means. It looks there are way too many places that could generate those indirect= lock chains that are hard to eliminate them all. Here is anther example, where= it has, console_owner -> port_lock port_lock -> zone_lock [=C2=A0=C2=A0297.425922] -> #3 (&(&zone->lock)->rlock){-.-.}: [=C2=A0=C2=A0297.425925]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0_= _lock_acquire+0x5b3/0xb40 [=C2=A0=C2=A0297.425925]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0l= ock_acquire+0x126/0x280 [=C2=A0=C2=A0297.425926]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0_= raw_spin_lock+0x2f/0x40 [=C2=A0=C2=A0297.425927]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0r= mqueue_bulk.constprop.21+0xb6/0x1160 [=C2=A0=C2=A0297.425928]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0g= et_page_from_freelist+0x898/0x22c0 [=C2=A0=C2=A0297.425928]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0_= _alloc_pages_nodemask+0x2f3/0x1cd0 [=C2=A0=C2=A0297.425929]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0a= lloc_pages_current+0x9c/0x110 [=C2=A0=C2=A0297.425930]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0a= llocate_slab+0x4c6/0x19c0 [=C2=A0=C2=A0297.425931]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0n= ew_slab+0x46/0x70 [=C2=A0=C2=A0297.425931]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0_= __slab_alloc+0x58b/0x960 [=C2=A0=C2=A0297.425932]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0_= _slab_alloc+0x43/0x70 [=C2=A0=C2=A0297.425933]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0_= _kmalloc+0x3ad/0x4b0 [=C2=A0=C2=A0297.425933]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0_= _tty_buffer_request_room+0x100/0x250 [=C2=A0=C2=A0297.425934]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0t= ty_insert_flip_string_fixed_flag+0x67/0x110 [=C2=A0=C2=A0297.425935]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0p= ty_write+0xa2/0xf0 [=C2=A0=C2=A0297.425936]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0n= _tty_write+0x36b/0x7b0 [=C2=A0=C2=A0297.425936]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0t= ty_write+0x284/0x4c0 [=C2=A0=C2=A0297.425937]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0_= _vfs_write+0x50/0xa0 [=C2=A0=C2=A0297.425938]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0v= fs_write+0x105/0x290 [=C2=A0=C2=A0297.425939]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0r= edirected_tty_write+0x6a/0xc0 [=C2=A0=C2=A0297.425939]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0d= o_iter_write+0x248/0x2a0 [=C2=A0=C2=A0297.425940]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0v= fs_writev+0x106/0x1e0 [=C2=A0=C2=A0297.425941]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0d= o_writev+0xd4/0x180 [=C2=A0=C2=A0297.425941]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0_= _x64_sys_writev+0x45/0x50 [=C2=A0=C2=A0297.425942]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0d= o_syscall_64+0xcc/0x76c [=C2=A0=C2=A0297.425943]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0e= ntry_SYSCALL_64_after_hwframe+0x49/0xbe