linux-kernel - Re: [PATCH v2 07/17] debugobjects: Move printk out of db lock critical sections

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: <20181123114826.h27t7qiwfp7grrqx@pathway.suse.cz>
Date:   Fri, 23 Nov 2018 12:48:26 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Waiman Long <longman@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v2 07/17] debugobjects: Move printk out of db lock
 critical sections

On Fri 2018-11-23 11:40:48, Sergey Senozhatsky wrote:
> On (11/22/18 11:16), Peter Zijlstra wrote:
> > > So maybe we need to switch debug objects print-outs to _always_
> > > printk_deferred(). Debug objects can be used in code which cannot
> > > do direct printk() - timekeeping is just one example.
> > 
> > No, printk_deferred() is a disease, it needs to be eradicated, not
> > spread around.
> 
> deadlock-free printk() is deferred, but OK.

The best solution would be lockless console drivers. Sigh.


> Another idea then:
> 
> ---
> 
> diff --git a/lib/debugobjects.c b/lib/debugobjects.c
> index 70935ed91125..3928c2b2f77c 100644
> --- a/lib/debugobjects.c
> +++ b/lib/debugobjects.c
> @@ -323,10 +323,13 @@ static void debug_print_object(struct debug_obj *obj, char *msg)
>  		void *hint = descr->debug_hint ?
>  			descr->debug_hint(obj->object) : NULL;
>  		limit++;
> +
> +		bust_spinlocks(1);
>  		WARN(1, KERN_ERR "ODEBUG: %s %s (active state %u) "
>  				 "object type: %s hint: %pS\n",
>  			msg, obj_states[obj->state], obj->astate,
>  			descr->name, hint);
> +		bust_spinlocks(0);
>  	}
>  	debug_objects_warnings++;
>  }
> 
> ---
> 
> This should make serial consoles re-entrant.
> So printk->console_driver_write() hopefully will not deadlock.

Is the re-entrance safe? Some risk might be acceptable in Oops/panic
situations. It is much less acceptable for random warnings.

Best Regards,
Petr