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Date: Fri, 23 Feb 2018 10:17:37 +0000
From: Luis Henriques <lhenriques@suse.com>
Subject: Re: [PATCH v2 6/8] fsstress: implement the clonerange/deduperange
 ioctls
Message-ID: <20180223101737.hihkmeykjmqgjko7@hermes.olymp>
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To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: eguan@redhat.com, linux-xfs@vger.kernel.org, fstests@vger.kernel.org
List-ID: <fstests@vger.kernel.org>

On Thu, Feb 22, 2018 at 10:34:45AM -0800, Darrick J. Wong wrote:
> On Thu, Feb 22, 2018 at 06:17:31PM +0000, Luis Henriques wrote:
> > On Thu, Feb 22, 2018 at 09:27:41AM -0800, Darrick J. Wong wrote:
> > > On Thu, Feb 22, 2018 at 04:06:14PM +0000, Luis Henriques wrote:
> > > > On Thu, Dec 14, 2017 at 06:07:31PM -0800, Darrick J. Wong wrote:
> > > >=20
> > > > <snip>
> > > >=20
> > > > > +void
> > > > > +clonerange_f(
> > > > > +	int			opno,
> > > > > +	long			r)
> > > > > +{
> > > >=20
> > > > <snip>
> > > >=20
> > > > > +	/* Calculate offsets */
> > > > > +	len =3D (random() % FILELEN_MAX) + 1;
> > > > > +	len &=3D ~(stat1.st_blksize - 1);
> > > > > +	if (len =3D=3D 0)
> > > > > +		len =3D stat1.st_blksize;
> > > > > +	if (len > stat1.st_size)
> > > > > +		len =3D stat1.st_size;
> > > > > +
> > > > > +	lr =3D ((__int64_t)random() << 32) + random();
> > > > > +	if (stat1.st_size =3D=3D len)
> > > > > +		off1 =3D 0;
> > > > > +	else
> > > > > +		off1 =3D (off64_t)(lr % MIN(stat1.st_size - len, MAXFSIZE));
> > > > > +	off1 %=3D maxfsize;
> > > > > +	off1 &=3D ~(stat1.st_blksize - 1);
> > > > > +
> > > > > +	/*
> > > > > +	 * If srcfile =3D=3D destfile, randomly generate destination =
ranges
> > > > > +	 * until we find one that doesn't overlap the source range.
> > > > > +	 */
> > > > > +	do {
> > > > > +		lr =3D ((__int64_t)random() << 32) + random();
> > > > > +		off2 =3D (off64_t)(lr % MIN(stat2.st_size + (1024 * 1024), M=
AXFSIZE));
> > > > > +		off2 %=3D maxfsize;
> > > > > +		off2 &=3D ~(stat2.st_blksize - 1);
> > > > > +	} while (stat1.st_ino =3D=3D stat2.st_ino && llabs(off2 - off=
1) < len);
> > > >=20
> > > > I started seeing hangs in generic/013 on cephfs.  After spending =
some
> > > > time looking, I found that this loops forever.  And the reason se=
ems to
> > > > be that stat1.st_blksize is too big for this filesystem (4M) -- w=
hen
> > > > doing:
> > >=20
> > > "Too big for this filesystem"?
> > >=20
> > > Uh... maybe you'd better start by giving me more stat buffer info -=
-
> > > what's st_size?
> > >=20
> > > > 	off1 &=3D ~(stat1.st_blksize - 1);
> > >=20
> > > These bits round the start offset down to block granularity, since =
clone
> > > range implementations generally require that the ranges align to bl=
ock
> > > boundaries.
> > >=20
> > > (Though AFAICT ceph doesn't support clone range anyway...)
> > >=20
> > > So reading between the lines, is the problem here that ceph adverti=
ses a
> > > blocksize of 4M and fsstress calls clonerange_f with files that are
> > > smaller than 4M in size, so the only possible offsets with a 4M
> > > blocksize are zero and that's why we end up looping forever?
> >=20
> > Brilliantly described!  That is *exactly* what I'm seeing and failed =
to
> > describe.  I guess I could use FSSTRESS_AVOID to work around this iss=
ue,
> > but there are probably better options.
>=20
> Better to patch fsstress.c against this bug. :)
>=20
> Does the following patch help?

Yes, it does.  Thanks!  Feel free to add my

Tested-by: Luis Henriques <lhenriques@suse.com>

Cheers,
--
Lu=EDs

>=20
> --D
>=20
> diff --git a/ltp/fsstress.c b/ltp/fsstress.c
> index 935f5de..e107099 100644
> --- a/ltp/fsstress.c
> +++ b/ltp/fsstress.c
> @@ -2222,6 +2222,7 @@ clonerange_f(
>  	off64_t			lr;
>  	off64_t			off1;
>  	off64_t			off2;
> +	off64_t			max_off2;
>  	size_t			len;
>  	int			v1;
>  	int			v2;
> @@ -2305,9 +2306,10 @@ clonerange_f(
>  	 * If srcfile =3D=3D destfile, randomly generate destination ranges
>  	 * until we find one that doesn't overlap the source range.
>  	 */
> +	max_off2 =3D MIN(stat2.st_size + (1024ULL * stat2.st_blksize), MAXFSI=
ZE);
>  	do {
>  		lr =3D ((int64_t)random() << 32) + random();
> -		off2 =3D (off64_t)(lr % MIN(stat2.st_size + (1024 * 1024), MAXFSIZE)=
);
> +		off2 =3D (off64_t)(lr % max_off2);
>  		off2 %=3D maxfsize;
>  		off2 &=3D ~(stat2.st_blksize - 1);
>  	} while (stat1.st_ino =3D=3D stat2.st_ino && llabs(off2 - off1) < len=
);
>=20