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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id o14sm1444386qtk.52.2019.10.09.07.46.15 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 09 Oct 2019 07:46:16 -0700 (PDT) Message-ID: <1570632374.5937.8.camel@lca.pw> Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk() From: Qian Cai To: Petr Mladek 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 Date: Wed, 09 Oct 2019 10:46:14 -0400 In-Reply-To: <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> <20191009142438.yx74ukfqwy2hr4fz@pathway.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: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2019-10-09 at 16:24 +0200, Petr Mladek wrote: > 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/ > > > > > > > > [  297.425964] -> #1 (&port_lock_key){-.-.}: > > > > [  297.425967]        __lock_acquire+0x5b3/0xb40 > > > > [  297.425967]        lock_acquire+0x126/0x280 > > > > [  297.425968]        _raw_spin_lock_irqsave+0x3a/0x50 > > > > [  297.425969]        serial8250_console_write+0x3e4/0x450 > > > > [  297.425970]        univ8250_console_write+0x4b/0x60 > > > > [  297.425970]        console_unlock+0x501/0x750 > > > > [  297.425971]        vprintk_emit+0x10d/0x340 > > > > [  297.425972]        vprintk_default+0x1f/0x30 > > > > [  297.425972]        vprintk_func+0x44/0xd4 > > > > [  297.425973]        printk+0x9f/0xc5 > > > > [  297.425974]        register_console+0x39c/0x520 > > > > [  297.425975]        univ8250_console_init+0x23/0x2d > > > > [  297.425975]        console_init+0x338/0x4cd > > > > [  297.425976]        start_kernel+0x534/0x724 > > > > [  297.425977]        x86_64_start_reservations+0x24/0x26 > > > > [  297.425977]        x86_64_start_kernel+0xf4/0xfb > > > > [  297.425978]        secondary_startup_64+0xb6/0xc0 > > > > > > > > where the report again show the early boot call trace for the locking > > > > dependency, > > > > > > > > console_owner --> port_lock_key > > > > > > > > but that dependency clearly not only happen in the early boot. > > > > > > Can you provide an example of the runtime dependency without any early > > > boot artifacts? Because this discussion really doens't make much sense > > > without a clear example of a _real_ lockdep report that is not a false > > > possitive. All of them so far have been concluded to be false possitive > > > AFAIU. > > > > 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. > > > > 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. Now the bar is higher again. You are now asking me to actually trigger this potential deadlock live. I am probably better off buying some lottery tickets then if I could be that lucky.