linux-kernel - Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1570628593.5937.3.camel@lca.pw>
Date:   Wed, 09 Oct 2019 09:43:13 -0400
From:   Qian Cai <cai@....pw>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        sergey.senozhatsky.work@...il.com, rostedt@...dmis.org,
        peterz@...radead.org, linux-mm@...ck.org,
        john.ogness@...utronix.de, akpm@...ux-foundation.org,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>, david@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()

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