bug in spinlock.c?

[Karsten Keil]

On Fri, Feb 21, 2003 at 05:17:59PM +0100, Wolfram Gloger wrote:
> > Looking at the ex18 hang (sometimes ex18 even segfaulted) on x86-64,
> > Karsten noticed that we allocate a struct wait_node in
> > __pthread_alt_lock on the stack - and put it somehow also on the list
> > of waiting nodes.
> 
> Yes.
> 
> > In __pthread_alt_unlock we go through the waiting nodes and deque it.
> > 
> > This looks broken, since we allocate something on the stack of a
> > function and leave the function with this data hanging around.
> 
> ??  No, the function __pthread_alt_lock is not left until the
> wait_node has been signalled, check all the suspend(self); calls.
> Basically, all this works because only one function can acquire the
> lock.
> 

Yes I found this by my self after some brainstorming :-), but it
was the first impression, that this code may be the reason for the
destroyed p_lock->next (set to something else, but not a valid pointer).

Thanks for confirmation.

> > Can somebody confirm this?  Or do you have other ideas that would
> > explain the segfaults we noticed?  gdb pointed to this code,
> 
> I've also seen gdb stacktraces like this many times, however the
> actual spinlock code in LinuxThreads never was at fault, it was always
> a double unlock or similar..
> 
> Regards,
> Wolfram.

-- 
Karsten Keil
SuSE Labs
ISDN development