lkml.org 
[lkml]   [2007]   [Oct]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: BUG: lock held when returning to user space
From
Date

On Sat, 2007-10-27 at 17:12 +0200, Jiri Kosina wrote:
> On Sat, 27 Oct 2007, Gabriel C wrote:
>
> > I found that today in dmesg after booting current git (
> > ec3b67c11df42362ccda81261d62829042f223f0 ) :
> > ...
> > [ 592.752777]
> > [ 592.752781] ================================================
> > [ 592.753478] [ BUG: lock held when returning to user space! ]
> > [ 592.753880] ------------------------------------------------
> > [ 592.754262] hwclock/1452 is leaving the kernel with locks still held!
> > [ 592.754655] 1 lock held by hwclock/1452:
> > [ 592.755007] #0: (&rtc->char_lock){--..}, at: [<c02a7ebb>] rtc_dev_open+0x2e/0x7e
>
> Yes, this is because rtc keeps a char_lock mutex locked as long as the
> device is open, to avoid concurrent accessess.
>
> It could be easily substituted by some counting -- setting and clearing
> bit in struct rtc_device instead of using char_lock, but doing this just
> to shut the lockdep off is questionable imho.
>
> Peter, what is the preferred way to annotate these kinds of locking for
> lockdep to express that it is intended?

Not sure, I'd not thought that anyone would actually want to do this.
I'm also not sure how I stand on this, I'd prefer to say: don't do this!

I think, in this case, the lock is associated with a kernel object that
is properly cleaned up if the holding tasks gets a SIGKILL. But in
general I'd like to see this kind of thing go away.

Now I could probably come up with an annotation to hide it, but what do
other people think, Ingo, Linus, Andrew, do we want to keep kernel locks
held over userspace?



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

\
 
 \ /
  Last update: 2007-10-27 17:33    [from the cache]
©2003-2011 Jasper Spaans