linux-kernel - Re: [PATCH] panic: move bust_spinlocks(0) after console_flush_on

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-Id: <20180620143004.9dd0cf834acfcff5bd1bcb58@linux-foundation.org>
Date:   Wed, 20 Jun 2018 14:30:04 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Hoeun Ryu <hoeun.ryu@....com.com>
Cc:     Kees Cook <keescook@...omium.org>, Borislav Petkov <bp@...e.de>,
        Andi Kleen <ak@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Hoeun Ryu <hoeun.ryu@....com>, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH] panic: move bust_spinlocks(0) after
 console_flush_on_panic() to avoid deadlocks

On Mon,  4 Jun 2018 14:45:57 +0900 Hoeun Ryu <hoeun.ryu@....com.com> wrote:

> From: Hoeun Ryu <hoeun.ryu@....com>
> 
>  Many console device drivers hold the uart_port->lock spinlock with irq enabled
> (using spin_lock()) while the device drivers are writing characters to their devices,
> but the device drivers just try to hold the spin lock (using spin_trylock()) if
> "oops_in_progress" is equal or greater than 1 to avoid deadlocks.
> 
>  There is a case ocurring a deadlock related to the lock and oops_in_progress. A CPU
> could be stopped by smp_send_stop() while it was holding the port lock because irq was
> enabled. Once a CPU stops, it doesn't respond interrupts anymore and the lock stays
> locked forever.
> 
>  console_flush_on_panic() is called during panic() and it eventually holds the uart
> lock but the lock is held by another stopped CPU and it is a deadlock. By moving
> bust_spinlocks(0) after console_flush_on_panic(), let the console device drivers
> think the Oops is still in progress to call spin_trylock() instead of spin_lock() to
> avoid the deadlock.

hm.  Sergey, is this at all related to the UART printk deadlock change
which you're presently discussing in
http://lkml.kernel.org/r/20180615093919.559-1-sergey.senozhatsky@gmail.com?

> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -233,8 +233,6 @@ void panic(const char *fmt, ...)
>  	if (_crash_kexec_post_notifiers)
>  		__crash_kexec(NULL);
>  
> -	bust_spinlocks(0);
> -
>  	/*
>  	 * We may have ended up stopping the CPU holding the lock (in
>  	 * smp_send_stop()) while still having some valuable data in the console
> @@ -246,6 +244,8 @@ void panic(const char *fmt, ...)
>  	debug_locks_off();
>  	console_flush_on_panic();
>  
> +	bust_spinlocks(0);
> +
>  	if (!panic_blink)
>  		panic_blink = no_blink;
>