Re: tmpfs module and pool allocator

[jnemeth%victoria.tc.ca@localhost (John Nemeth)]

On May 22,  3:58pm, Bernd Ernesti wrote:
} On Wed, Dec 30, 2009 at 01:03:50PM -0500, Elad Efrat wrote:
} > 
} > >I've "fixed it" by explicitly calling mutex_destroy() in
} > >tmpfs_modcmd():MODULE_CMD_FINI, but I think the right fix would be to
} > >set a flag indicating that the pool allocator used is not a "system
} > >allocator" (or that it is a "custom allocator", or whatever) and
} > >should be destroyed as well, or at least its mutex...
} > 
} > Matt@ suggested we use a reference count on the pool allocator instead
} > of the PA_INITIALIZED flag, and when it drops to zero, pool_destroy can
} > destroy the mutex as well.
} > 
} > I've attached a diff that supposedly implements it... But I don't know
} > if it's correct. It fixes the problem for me, on a GEENRIC kernel built
} > with DIAGNOSTIC and LOCKDEBUG.
} > 
} > Please have a look and let me know if it's okay to commit.
} 
} I can't comment if it is okay or not, but see below.
} 
} > Index: sys/pool.h
} > ===================================================================
} > RCS file: /cvsroot/src/sys/sys/pool.h,v
} > retrieving revision 1.67
} > diff -u -p -r1.67 pool.h
} > --- sys/pool.h      15 Oct 2009 20:50:12 -0000      1.67
} > +++ sys/pool.h      30 Dec 2009 17:58:17 -0000
} > @@ -64,7 +64,7 @@ struct pool_allocator {
} >     kmutex_t        pa_lock;
} >     TAILQ_HEAD(, pool) pa_list;     /* list of pools using this allocator */
} >     int             pa_flags;
} > -#define    PA_INITIALIZED  0x01
} > +   uint32_t        pa_refcnt;      /* number of pools using this allocator 
*/
} >     int             pa_pagemask;
} >     int             pa_pageshift;
} >     struct vm_map *pa_backingmap;
} 
} You are adding a new field in the middle of a struct.
} Is that really ok?

     Since it isn't a struct that userland will see, there is no compat
issue.  If it is at all possible that a module will see it, then the
kernel version needs to be bumped (it would need to be bumped
regardless of where the field is added).

}-- End of excerpt from Bernd Ernesti