> Date: Sun, 3 Jun 2018 13:51:19 +0200 (CEST)
> From: Mark Kettenis <[email protected]>
>
> > Date: Sat, 2 Jun 2018 15:08:14 -0700
> > From: Philip Guenther <[email protected]>
> >
> > On Sat, 2 Jun 2018, Christophe Prévotaux wrote:
> > > This a witness report I got on boot with snapshot Jun 1st amd64
> > >
> > > root on sd0a (9b49e3196b9bfae8.a) swap on sd0b dump on sd0b
> > > lock order reversal:
> > > 1st 0xffffff021cdac180 vmmaplk (&map->lock) @
> > > /usr/src/sys/uvm/uvm_map.c:4433
> > > 2nd 0xffffff01dc5f71a8 inode (&ip->i_lock)
> >
> > I believe uvm and the vnode layer handle this correctly, with lock tries
> > that fall back to releasing the other lock and retrying so progress is
> > made. The fix for WITNESS complaining is to mark vmmaplk as a vnode lock.
> >
> > ok?
>
> I don't think so. While we have UVM_FLAG_TRYLOCK, I don't think it is
> used in the code paths shown in the original report.
>
> This may still be a false positive though. Non-kernel maps will
> experience different locking patterns and their locks should probably
> be considered to be a different class than the lock associated with
> the kernel map.
>
> That said I think the kernel could end up mapping files into kernel
> address space as well so I think this lock order reversal is real. A
> way to avoid this is to change the pool allocator used for the
> dirhash. The pool entries are smaller than a page, so I think
> pool_allocator_single is the appropriate choice here.
But this doesn't fix the lock order reversal triggered by
regress/sys/kern/mmap, so maybe ignore this for now.
> Index: ufs/ufs/ufs_dirhash.c
> ===================================================================
> RCS file: /cvs/src/sys/ufs/ufs/ufs_dirhash.c,v
> retrieving revision 1.40
> diff -u -p -r1.40 ufs_dirhash.c
> --- ufs/ufs/ufs_dirhash.c 26 Oct 2017 02:38:54 -0000 1.40
> +++ ufs/ufs/ufs_dirhash.c 3 Jun 2018 11:50:11 -0000
> @@ -1053,7 +1053,7 @@ void
> ufsdirhash_init(void)
> {
> pool_init(&ufsdirhash_pool, DH_NBLKOFF * sizeof(doff_t), 0, IPL_NONE,
> - PR_WAITOK, "dirhash", NULL);
> + PR_WAITOK, "dirhash", &pool_allocator_single);
> rw_init(&ufsdirhash_mtx, "dirhash_list");
> arc4random_buf(&ufsdirhash_key, sizeof(ufsdirhash_key));
> TAILQ_INIT(&ufsdirhash_list);
>
>
>
