Messages in this thread | | | Date | Thu, 9 Jun 2011 22:27:07 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/3] printk: Release console_sem after logbuf_lock |
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* Andrew Morton <akpm@linux-foundation.org> wrote:
> On Thu, 09 Jun 2011 15:06:48 +0200 > Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > > > Release console_sem after unlocking the logbuf_lock so that we don't > > generate wakeups while holding logbuf_lock. This avoids some lock > > inversion troubles once we remove the lockdep_off bits between > > logbuf_lock and rq->lock (prints while holding rq->lock vs doing > > wakeups while holding logbuf_lock). > > > > There's of course still an actual deadlock where the printk()s under > > rq->lock will issue a wakeup from the up() call. > > > > ... > > > > @@ -1271,8 +1273,8 @@ void console_unlock(void) > > if (unlikely(exclusive_console)) > > exclusive_console = NULL; > > > > - up(&console_sem); > > spin_unlock_irqrestore(&logbuf_lock, flags); > > + up(&console_sem); > > if (wake_klogd) > > wake_up_klogd(); > > } > > I have a horrible feeling that I put the up() inside logbuf_lock for > Special And Cunning Reasons. But I'm struggling to work out what they > might have been and my archives only go back to October 2000(!). > > Hate it when that happens.
Heh, here's what i told Peter two days ago when i saw that chunk:
=> Subject: printk: Release console_sem after logbuf_lock => i have some vague memories about some sort of complication in that area ... => but don't remember the specifics => only a 'there be dragons' mental marker
and i have to say that when i found a boot lockup during testing i was not surprised very much :)
Thanks,
Ingo
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