linux-kernel - Re: [RFC][PATCHv2 1/4] panic: avoid deadlocks in re-entrant console drivers

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: <20181023121057.GC10251@jagdpanzerIV>
Date:   Tue, 23 Oct 2018 21:12:30 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Daniel Wang <wonderfly@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Jiri Slaby <jslaby@...e.com>,
        Peter Feiner <pfeiner@...gle.com>,
        linux-serial@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCHv2 1/4] panic: avoid deadlocks in re-entrant console
 drivers

On (10/23/18 21:04), Sergey Senozhatsky wrote:
> 
> Seems that s390 is the only arch which defines its own bust_spinlocks().
> Not sure why... Just to play games with console_loglevel?
> 
> ---
> 
> void bust_spinlocks(int yes)
> {
> 	if (yes) {
> 		oops_in_progress = 1;
> 	} else {
> 		int loglevel_save = console_loglevel;
> 		console_unblank();
> 		oops_in_progress = 0;
> 		/*
> 		 * OK, the message is on the console.  Now we call printk()
> 		 * without oops_in_progress set so that printk will give klogd
> 		 * a poke.  Hold onto your hats...
> 		 */
> 		console_loglevel = 15;
> 		printk(" ");
> 		console_loglevel = loglevel_save;
> 	}
> }
> 
> ---
> 
> The "printk(" "); without oops_in_progress" part is a bit worrisome.
> This thing technically can deadlock. Unless s390 has no NMI panic().

And console_unblank() is not guaranteed to print anything (unlike
console_flush_on_panic(), but oops is not panic() yet, so we can't
replace it with flush_on_panic()) - console_sem can be locked, so
console_unblank() would do nothing.

That printk(" ") probably wants to be printk_deferred(" ").

	-ss