FreeLists / haiku-gsoc / [haiku-gsoc] [HCD]: Bfs bug #1

["Salvatore Benedetto" <emitrax@xxxxxxxxx>]

Hi there,

it looks like I hit my first bug (#2400) while unpacking a tarball
containing the whole haiku tree
(about 480MB compressed) from a usbstick while running in vmware.

Last night, I followed the stack trace to figure out the crash.
The destructor of VNode is called I guess, because the constructor for
some reason fails to
create the object due to memory problem as the constructor seems
pretty straightforward to me.
        Vnode(Volume *volume, ino_t id)
            :
            fVolume(volume),
            fID(id)
        {
        }
Here is a summary:
Index::SetTo() is called, it tries to create a Vnode object
Vnode vnode(fVolume, id); thus with this signature Vnode(Volume
*volume, ino_t id),
but then the destructor gets called.

Actually, now that I look at it, it might fail because the Volume
constructor fails first.
I'm not C++ guru, but I thought that if one of the initialization
would fail, the object wouldn't
be created without any needs to call the destructor.

Anyhow, the ~Vnode gets called, that in turn calls Put()
        void Put()
       {
           if (fVolume)
               put_vnode(fVolume->FSVolume(), fID);
           fVolume = NULL;
       }
...
   dec_vnode_ref_count(vnode, false);
...
   int32 oldRefCount = atomic_add(&vnode->ref_count, -1);
   ASSERT( oldRefCount > 0)
...
KDL.

By the way, two things about atomic_add:
1. As already stated in the comment above the function, it is in a unusual place
src/add-ons/kernel/partitioning_systems/intel/intel.cpp
2. How is it atomic? I don't see where the interrupts are disabled.

Any comments?

Regards,
--
Salvatore Benedetto (a.k.a. emitrax)
Student of Computer Engineer
University of Pisa
www.haiku-os.it