Mark Kettenis wrote:
> > Date: Mon, 28 May 2018 11:23:47 +0200
> > From: Martin Pieuchot <m...@openbsd.org>
> > 
> > As found by tb@ and visa@, `f_mtx' need to block interrupts as long as
> > it can be taken w/ and w/o the KERNEL_LOCK().  Otherwise a deadlock is
> > possible if an interrupt tries to grab the KERNEL_LOCK().
> > 
> > I'm not switching to a rwlock because code paths are short, I don't
> > want to introduce new sleeping points and in the long run we should
> > be using SRPs or atomic operations for reference counts.
> > 
> > ok?
> 
> I suppose IPL_VM is the most sensible default for mutexes that need to
> block all interrupts that might need the kernel lock.
> 
> ok kettenis@


Hello,

Wouldn't IPL_MPFLOOR be more appropriate? After all mutexes are already
raising the ipl level to IPL_MPFLOOR (expect for IPL_NONE and above).


Mathieu-.

> 
> > Index: kern/kern_descrip.c
> > ===================================================================
> > RCS file: /cvs/src/sys/kern/kern_descrip.c,v
> > retrieving revision 1.158
> > diff -u -p -r1.158 kern_descrip.c
> > --- kern/kern_descrip.c     8 May 2018 09:03:58 -0000       1.158
> > +++ kern/kern_descrip.c     28 May 2018 09:23:31 -0000
> > @@ -957,7 +957,11 @@ restart:
> >      */
> >     numfiles++;
> >     fp = pool_get(&file_pool, PR_WAITOK|PR_ZERO);
> > -   mtx_init(&fp->f_mtx, IPL_NONE);
> > +   /*
> > +    * We need to block interrupts as long as `f_mtx' is being taken
> > +    * with and without the KERNEL_LOCK().
> > +    */
> > +   mtx_init(&fp->f_mtx, IPL_VM);
> >     fp->f_iflags = FIF_LARVAL;
> >     if ((fq = p->p_fd->fd_ofiles[0]) != NULL) {
> >             LIST_INSERT_AFTER(fq, fp, f_list);
> > 
> > 
> 

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