> 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@
> 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);
>
>
