Date: Fri, 4 Jul 2014 12:32:51 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Adrian Chadd <adrian.chadd@gmail.com> Cc: freebsd-current <freebsd-current@freebsd.org>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: EDEADLK from fcntl(F_SETFL) ? Message-ID: <20140704093251.GF93733@kib.kiev.ua> In-Reply-To: <CAJ-VmonS6r2tbNtk73iAeJCSUJfqDc=WY8B2Y6SDKNsQajb3PA@mail.gmail.com> References: <CAJ-Vmo=szh6rk5s1H5mZXQZwvm2YZjBK5LQkLoOOZyQT6yhMjw@mail.gmail.com> <CAJ-VmonS6r2tbNtk73iAeJCSUJfqDc=WY8B2Y6SDKNsQajb3PA@mail.gmail.com>
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On Thu, Jul 03, 2014 at 07:15:51PM -0700, Adrian Chadd wrote:
> Hi,
>=20
> I'm currently testing this out. It seems to be working out alright.
>=20
> adrian@test3:~/work/freebsd % svn diff stable/10/src/sys/kern/
>=20
> Index: stable/10/src/sys/kern/kern_lockf.c
>=20
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>=20
> --- stable/10/src/sys/kern/kern_lockf.c (revision 267627)
>=20
> +++ stable/10/src/sys/kern/kern_lockf.c (working copy)
>=20
> @@ -1425,6 +1425,14 @@
>=20
> if (lockf_debug & 1)
>=20
> lf_print("lf_setlock: deadlock", lock);
>=20
> #endif
>=20
> +
>=20
> + /*
>=20
> + * If the lock isn't waiting, return EAGAIN
>=20
> + * rather than EDEADLK.
>=20
> + */
>=20
> + if (((lock->lf_flags & F_WAIT) =3D=3D 0) &&
>=20
> + (error =3D=3D EDEADLK))
>=20
> + error =3D EAGAIN;
>=20
> lf_free_lock(lock);
>=20
> goto out;
>=20
> }
>=20
> On 3 July 2014 17:45, Adrian Chadd <adrian.chadd@gmail.com> wrote:
> > Hi!
> >
> > I've seen sqlite3 crap out due to "disk IO error". It looks like the
> > F_SETFL path is returning EDEADLK when it shouldn't be - only the
> > "wait" version of this should be.
> >
> > The kernel code looks to be:
> >
> > lf_setlock() -> lf_add_outgoing() -> lf_add_edge() -> graph_add_edge()
> > -> EDEADLK
> >
> > .. and lf_setlock() will return an error from lf_add_outgoing()
> > without checking if it's (a) EDEADLK, and (b) whether we're going to
> > sleep or not.
> >
> > So, sqlite3 trips up on this. I'm sure other things do. What should
> > the correct thing be? It looks like EWOULDBLOCK is the correct value
> > to return for F_SETFL failing, not EDEADLK.
> >
> > What do those-who-know-POSIX-standards-better-than-I think?
I doubt that the patch is correct. If there is an issue in kernel, the
patch only hides it.
Note that lf_setlock() first calls lf_getblock() to verify that there
is no contending lock on the range, and if there is a conflicting lock,
the very first statement inside the if() checks for F_WAIT.
Either you get a real deadlock, or there is a bug elsewere.
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