On Tue, 18 Sep 2007 12:30:52 +0200 Nadia Derbey <[email protected]> wrote:
> Andrew Morton wrote:
> > On Tue, 18 Sep 2007 13:17:28 +0400 Alexey Dobriyan <[email protected]> wrote:
> >
> >
> >>I'm getting tons of this, and X fails to start
> >>
> >>CONFIG_SYSVIPC=y
> >>CONFIG_SYSVIPC_SYSCTL=y
> >># CONFIG_PREEMPT_NONE is not set
> >># CONFIG_PREEMPT_VOLUNTARY is not set
> >>CONFIG_PREEMPT=y
> >>CONFIG_PREEMPT_BKL=y
> >>CONFIG_DEBUG_PREEMPT=y
> >>
> >>BUG: sleeping function called from invalid context at kernel/rwsem.c:47
> >>in_atomic():1, irqs_disabled():0
> >>no locks held by X/5879.
> >> [<c012bcb1>] down_write+0x15/0x50
> >> [<c01b53af>] do_shmat+0x235/0x3a0
> >> [<c0106be2>] sys_ipc+0x146/0x263
> >> [<c0102892>] sysenter_past_esp+0xa7/0xb5
> >> [<c0102856>] sysenter_past_esp+0x6b/0xb5
> >> =======================
> >
> >
> > Here's a bug:
> >
> > --- a/ipc/util.c~ipc-integrate-ipc_checkid-into-ipc_lock-fix-2
> > +++ a/ipc/util.c
> > @@ -691,7 +691,7 @@ struct kern_ipc_perm *ipc_lock(struct ip
> > rcu_read_unlock();
> > return ERR_PTR(-EINVAL);
> > }
> > -
> > + rcu_read_unlock();
> > return out;
> > }
> >
>
> Andrew,
>
> Actually the rcu_read_lock is released in ipc_unlock().
I agree it should be, but it isn't.
> So I think we
> shouldn't add an rcu_read_unlock() before leaving ipc_lock().
> This is a part that has not changed since the ref code.
>
Well, it was an optimisation. spin_lock() implies rcu_read_lock(). That's
a bit dirty and we might choose to not do that.
Would be interested in knowing the locking rules in there. For example,
this:
/**
* ipc_findkey - find a key in an ipc identifier set
* @ids: Identifier set
* @key: The key to find
*
* Requires ipc_ids.mutex locked.
* Returns the LOCKED pointer to the ipc structure if found or NULL
* if not.
* If key is found ipc contains its ipc structure
*/
appears to be hopelessly out of date?
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