linux-kernel - Re: [ANNOUNCE] 3.2.9-rt17

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]

Date:	Thu, 08 Mar 2012 13:42:39 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: [ANNOUNCE] 3.2.9-rt17

On Thu, 2012-03-08 at 19:28 +0100, Peter Zijlstra wrote:
> On Thu, 2012-03-08 at 13:23 -0500, Steven Rostedt wrote:
> > So basically what you tried to do was just set the owner of the lock to
> > have the priority of the task that wants the lock, until it releases it?
> > But by doing it without having this task sleep? 
> 
> No, by having it sleep ;-)
> 

That was the second part of my email.

> So you do the full PI sleeping lock thing, except you return fail if you
> loose the acquisition race on wakeup and you mark this waiter as
> 'special'.
> 
> Then on every rt_mutex block you have to do a deadlock analysis on the
> PI blocking chain (preferably shared with PI boost traversal of said
> chain), during that scan you collect all special tagged waiters.
> 
> If you find a deadlock, wake all these special waiters and have them
> return -EDEADLK.
> 
> I guess you could also do the full spin_deadlock() and do away with the
> try part and purely rely on the deadlock detection.

But do you release the lock first? For example, we have:

@@ -410,7 +411,7 @@ static inline struct dentry *dentry_kill
        if (inode && !spin_trylock(&inode->i_lock)) {
 relock:
                seq_spin_unlock(&dentry->d_lock);
-               cpu_relax();
+               cpu_chill();
                return dentry; /* try again with same dentry */
        }

By doing the test at the trylock, we can easily hit the deadlock,
because we still hold dentry->d_lock. But by moving the block to the
cpu_chill(), then we are less likely to hit the deadlock.

Perhaps call it, cpu_chill_on_lock().

-- Steve


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/