Date: Sat, 17 Feb 2018 16:38:25 +0100 From: Mariusz Zaborski <oshogbo@freebsd.org> To: Mateusz Guzik <mjguzik@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: Where KASASERT fd < fdp->fd_nfiles should be? Message-ID: <20180217153825.GB61118@x-wing> In-Reply-To: <CAGudoHHikxaGiB4NvADDGubkXuHLR8rOys2hUvcOd%2BZ0K22=Tw@mail.gmail.com> References: <20180217150224.GA61118@x-wing> <CAGudoHHikxaGiB4NvADDGubkXuHLR8rOys2hUvcOd%2BZ0K22=Tw@mail.gmail.com>
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On Sat, Feb 17, 2018 at 04:23:40PM +0100, Mateusz Guzik wrote:
> On Sat, Feb 17, 2018 at 04:02:24PM +0100, Mariusz Zaborski wrote:
> >
> > KASSERT(fd >=3D 0 && fd < fdp->fd_nfiles,
> > ("%s: invalid fd=3D%d", __func__, fd));
> >
> >
> > My question and problem is do we need this KASSERT?
> > The fdget_locked checks if the fd is not larger then fd_lastfile.
> > But the code from fdinit suggest that fd_lastfile can be larger then
> fd_nfiles.
> > pjd@ suggested that it can go over size of the table fd_ofiles array:
> > while (fdp->fd_lastfile >=3D newfdp->fd_nfiles) {
> > FILEDESC_SUNLOCK(fdp);
> > fdgrowtable(newfdp, fdp->fd_lastfile + 1);
> > FILEDESC_SLOCK(fdp);
> > }
> >
> > So the question is do we need this assertion here or maybe should we mo=
ve
> it to
> > the fget_locked()/fdget_locked() functions?
> >
>=20
> While the assertion arguably can be removed, it is most definitely
> valid.
>=20
> fd_nfiles signifies the size of the table, while fd_lastfile the highest
> used slot. By definition it must fit the table.
>=20
> The code sample is used on fork where the existing table is duplicated.
> Allocation of the new table is performed with locks dropped, which means
> the old one can grow in the meantime. The while loop ensures the new
> table will have the right size no matter what.
So maybe we should go in more general approach and move this KASSERT to the
fget_locked and fdget_locked functions?
Thanks,
--=20
Mariusz Zaborski
oshogbo//vx | http://oshogbo.vexillium.org
FreeBSD commiter | https://freebsd.org
Software developer | http://wheelsystems.com
If it's not broken, let's fix it till it is!!1
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