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:
> > >
> > > <snip>
> > >
> > > > +void
> > > > +clonerange_f(
> > > > + int opno,
> > > > + long r)
> > > > +{
> > >
> > > <snip>
> > >
> > > > + /* Calculate offsets */
> > > > + len = (random() % FILELEN_MAX) + 1;
> > > > + len &= ~(stat1.st_blksize - 1);
> > > > + if (len == 0)
> > > > + len = stat1.st_blksize;
> > > > + if (len > stat1.st_size)
> > > > + len = stat1.st_size;
> > > > +
> > > > + lr = ((__int64_t)random() << 32) + random();
> > > > + if (stat1.st_size == len)
> > > > + off1 = 0;
> > > > + else
> > > > + off1 = (off64_t)(lr % MIN(stat1.st_size - len, MAXFSIZE));
> > > > + off1 %= maxfsize;
> > > > + off1 &= ~(stat1.st_blksize - 1);
> > > > +
> > > > + /*
> > > > + * If srcfile == destfile, randomly generate destination ranges
> > > > + * until we find one that doesn't overlap the source range.
> > > > + */
> > > > + do {
> > > > + lr = ((__int64_t)random() << 32) + random();
> > > > + off2 = (off64_t)(lr % MIN(stat2.st_size + (1024 * 1024), MAXFSIZE));
> > > > + off2 %= maxfsize;
> > > > + off2 &= ~(stat2.st_blksize - 1);
> > > > + } while (stat1.st_ino == stat2.st_ino && llabs(off2 - off1) < len);
> > >
> > > I started seeing hangs in generic/013 on cephfs. After spending some
> > > time looking, I found that this loops forever. And the reason seems to
> > > be that stat1.st_blksize is too big for this filesystem (4M) -- when
> > > doing:
> >
> > "Too big for this filesystem"?
> >
> > Uh... maybe you'd better start by giving me more stat buffer info --
> > what's st_size?
> >
> > > off1 &= ~(stat1.st_blksize - 1);
> >
> > These bits round the start offset down to block granularity, since clone
> > range implementations generally require that the ranges align to block
> > boundaries.
> >
> > (Though AFAICT ceph doesn't support clone range anyway...)
> >
> > So reading between the lines, is the problem here that ceph advertises 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?
>
> Brilliantly described! That is *exactly* what I'm seeing and failed to
> describe. I guess I could use FSSTRESS_AVOID to work around this issue,
> but there are probably better options.
Better to patch fsstress.c against this bug. :)
Does the following patch help?
--D
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 == destfile, randomly generate destination ranges
* until we find one that doesn't overlap the source range.
*/
+ max_off2 = MIN(stat2.st_size + (1024ULL * stat2.st_blksize), MAXFSIZE);
do {
lr = ((int64_t)random() << 32) + random();
- off2 = (off64_t)(lr % MIN(stat2.st_size + (1024 * 1024), MAXFSIZE));
+ off2 = (off64_t)(lr % max_off2);
off2 %= maxfsize;
off2 &= ~(stat2.st_blksize - 1);
} while (stat1.st_ino == stat2.st_ino && llabs(off2 - off1) < len);
--
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