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Wed, 9 Oct 2019 14:24:39 +0000 (UTC) Date: Wed, 9 Oct 2019 16:24:38 +0200 From: Petr Mladek To: Qian Cai Cc: Michal Hocko , Christian Borntraeger , Heiko Carstens , sergey.senozhatsky.work@gmail.com, rostedt@goodmis.org, peterz@infradead.org, linux-mm@kvack.org, john.ogness@linutronix.de, akpm@linux-foundation.org, Vasily Gorbik , PeterOberparleiter , david@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk() Message-ID: <20191009142438.yx74ukfqwy2hr4fz@pathway.suse.cz> References: <1570550917.5576.303.camel@lca.pw> <20191008183525.GQ6681@dhcp22.suse.cz> <1570561573.5576.307.camel@lca.pw> <20191008191728.GS6681@dhcp22.suse.cz> <1570563324.5576.309.camel@lca.pw> <20191009114903.aa6j6sa56z2cssom@pathway.suse.cz> <1570626402.5937.1.camel@lca.pw> <20191009132746.GA6681@dhcp22.suse.cz> <1570628593.5937.3.camel@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To:<1570628593.5937.3.camel@lca.pw> User-Agent: NeoMutt/20170912 (1.9.0) Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed 2019-10-09 09:43:13, Qian Cai wrote: > On Wed, 2019-10-09 at 15:27 +0200, Michal Hocko wrote: > > On Wed 09-10-19 09:06:42, Qian Cai wrote: > > [...] > > > https://lore.kernel.org/linux-mm/1570460350.5576.290.camel@lca.pw/ > > >=20 > > > [=A0=A0297.425964] -> #1 (&port_lock_key){-.-.}: > > > [=A0=A0297.425967]=A0=A0=A0=A0=A0=A0=A0=A0__lock_acquire+0x5b3/0xb4= 0 > > > [=A0=A0297.425967]=A0=A0=A0=A0=A0=A0=A0=A0lock_acquire+0x126/0x280 > > > [=A0=A0297.425968]=A0=A0=A0=A0=A0=A0=A0=A0_raw_spin_lock_irqsave+0x= 3a/0x50 > > > [=A0=A0297.425969]=A0=A0=A0=A0=A0=A0=A0=A0serial8250_console_write+= 0x3e4/0x450 > > > [=A0=A0297.425970]=A0=A0=A0=A0=A0=A0=A0=A0univ8250_console_write+0x= 4b/0x60 > > > [=A0=A0297.425970]=A0=A0=A0=A0=A0=A0=A0=A0console_unlock+0x501/0x75= 0 > > > [=A0=A0297.425971]=A0=A0=A0=A0=A0=A0=A0=A0vprintk_emit+0x10d/0x340 > > > [=A0=A0297.425972]=A0=A0=A0=A0=A0=A0=A0=A0vprintk_default+0x1f/0x30 > > > [=A0=A0297.425972]=A0=A0=A0=A0=A0=A0=A0=A0vprintk_func+0x44/0xd4 > > > [=A0=A0297.425973]=A0=A0=A0=A0=A0=A0=A0=A0printk+0x9f/0xc5 > > > [=A0=A0297.425974]=A0=A0=A0=A0=A0=A0=A0=A0register_console+0x39c/0x= 520 > > > [=A0=A0297.425975]=A0=A0=A0=A0=A0=A0=A0=A0univ8250_console_init+0x2= 3/0x2d > > > [=A0=A0297.425975]=A0=A0=A0=A0=A0=A0=A0=A0console_init+0x338/0x4cd > > > [=A0=A0297.425976]=A0=A0=A0=A0=A0=A0=A0=A0start_kernel+0x534/0x724 > > > [=A0=A0297.425977]=A0=A0=A0=A0=A0=A0=A0=A0x86_64_start_reservations= +0x24/0x26 > > > [=A0=A0297.425977]=A0=A0=A0=A0=A0=A0=A0=A0x86_64_start_kernel+0xf4/= 0xfb > > > [=A0=A0297.425978]=A0=A0=A0=A0=A0=A0=A0=A0secondary_startup_64+0xb6= /0xc0 > > >=20 > > > where=A0the report again show the early boot call trace for the loc= king > > > dependency, > > >=20 > > > console_owner --> port_lock_key > > >=20 > > > but that dependency clearly not only happen in the early boot. > >=20 > > Can you provide an example of the runtime dependency without any earl= y > > boot artifacts? Because this discussion really doens't make much sens= e > > without a clear example of a _real_ lockdep report that is not a fals= e > > possitive. All of them so far have been concluded to be false possiti= ve > > AFAIU. >=20 > An obvious one is in the above link. Just replace the trace in #1 above= with > printk() from anywhere, i.e., just ignore the early boot calls there as= they are > not important. >=20 > printk() > console_unlock() > console_lock_spinning_enable() --> console_owner_lock > call_console_drivers() > serial8250_console_write() --> port->lock Please, find the location where this really happens and then suggests how the real deadlock could get fixed. So far, we have seen only false positives and theoretical scenarios. Best Regards, Petr