* [PATCH] xfs: Fix rounding in xfs_alloc_fix_len()
@ 2014-06-04 9:48 Jan Kara
2014-06-04 13:35 ` Brian Foster
0 siblings, 1 reply; 4+ messages in thread
From: Jan Kara @ 2014-06-04 9:48 UTC (permalink / raw
To: xfs; +Cc: Jan Kara
Rounding in xfs_alloc_fix_len() is wrong. As the comment states, the
result should be a number of a form (k*prod+mod) however due to sign
mistake the result is different. As a result allocations on raid arrays
could be misaligned in some cases.
This also seems to fix occasional assertion failure:
XFS_WANT_CORRUPTED_GOTO(rlen <= flen, error0)
in xfs_alloc_ag_vextent_size().
Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/xfs/xfs_alloc.c | 14 ++++++--------
1 file changed, 6 insertions(+), 8 deletions(-)
diff --git a/fs/xfs/xfs_alloc.c b/fs/xfs/xfs_alloc.c
index c1cf6a336a72..6a0281b16451 100644
--- a/fs/xfs/xfs_alloc.c
+++ b/fs/xfs/xfs_alloc.c
@@ -257,14 +257,12 @@ xfs_alloc_fix_len(
k = rlen % args->prod;
if (k == args->mod)
return;
- if (k > args->mod) {
- if ((int)(rlen = rlen - k - args->mod) < (int)args->minlen)
- return;
- } else {
- if ((int)(rlen = rlen - args->prod - (args->mod - k)) <
- (int)args->minlen)
- return;
- }
+ if (k > args->mod)
+ rlen = rlen - (k - args->mod);
+ else
+ rlen = rlen - args->prod + (args->mod - k);
+ if ((int)rlen < (int)args->minlen)
+ return;
ASSERT(rlen >= args->minlen);
ASSERT(rlen <= args->maxlen);
args->len = rlen;
--
1.8.1.4
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http://oss.sgi.com/mailman/listinfo/xfs
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] xfs: Fix rounding in xfs_alloc_fix_len()
2014-06-04 9:48 [PATCH] xfs: Fix rounding in xfs_alloc_fix_len() Jan Kara
@ 2014-06-04 13:35 ` Brian Foster
2014-06-04 15:10 ` Jan Kara
0 siblings, 1 reply; 4+ messages in thread
From: Brian Foster @ 2014-06-04 13:35 UTC (permalink / raw
To: Jan Kara; +Cc: xfs
On Wed, Jun 04, 2014 at 11:48:13AM +0200, Jan Kara wrote:
> Rounding in xfs_alloc_fix_len() is wrong. As the comment states, the
> result should be a number of a form (k*prod+mod) however due to sign
> mistake the result is different. As a result allocations on raid arrays
> could be misaligned in some cases.
>
> This also seems to fix occasional assertion failure:
> XFS_WANT_CORRUPTED_GOTO(rlen <= flen, error0)
> in xfs_alloc_ag_vextent_size().
>
Do you happen to have a reproducer for this?
The meaning of args->prod (the structure definition comment calls it the
prod value) is not clear to me. I see that we set it to an extent
size hint if one exists (in xfs_bmap_btalloc()), so I'll go with that.
args->mod then becomes the modulo of the file offset against that
alignment hint.
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
> fs/xfs/xfs_alloc.c | 14 ++++++--------
> 1 file changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/fs/xfs/xfs_alloc.c b/fs/xfs/xfs_alloc.c
> index c1cf6a336a72..6a0281b16451 100644
> --- a/fs/xfs/xfs_alloc.c
> +++ b/fs/xfs/xfs_alloc.c
> @@ -257,14 +257,12 @@ xfs_alloc_fix_len(
We get here and take the extent length, mod against the alignment and
compare to the mod of the offset.
> k = rlen % args->prod;
> if (k == args->mod)
> return;
> - if (k > args->mod) {
> - if ((int)(rlen = rlen - k - args->mod) < (int)args->minlen)
> - return;
> - } else {
> - if ((int)(rlen = rlen - args->prod - (args->mod - k)) <
> - (int)args->minlen)
> - return;
> - }
> + if (k > args->mod)
> + rlen = rlen - (k - args->mod);
If the length mod is greater than the offset mod, reduce the length by
the delta of the mods.
> + else
> + rlen = rlen - args->prod + (args->mod - k);
Otherwise (length mod is less than offset mod), reduce by a full
alignment size and add back the difference to match the offset mod.
This seems correct to me.
> + if ((int)rlen < (int)args->minlen)
> + return;
> ASSERT(rlen >= args->minlen);
> ASSERT(rlen <= args->maxlen);
The rlen >= minlen assert seems kind of pointless here, but what about
changing both instances of these two asserts to the following:
ASSERT(rlen >= args->minlen && rlen <= args->maxlen);
... and add a new one after the length adjustment along the lines of:
ASSERT((rlen % args->prod) == args->mod);
Thoughts? Would this have caught the problem you've found earlier?
Brian
> args->len = rlen;
> --
> 1.8.1.4
>
> _______________________________________________
> xfs mailing list
> xfs@oss.sgi.com
> http://oss.sgi.com/mailman/listinfo/xfs
_______________________________________________
xfs mailing list
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http://oss.sgi.com/mailman/listinfo/xfs
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] xfs: Fix rounding in xfs_alloc_fix_len()
2014-06-04 13:35 ` Brian Foster
@ 2014-06-04 15:10 ` Jan Kara
2014-06-04 15:54 ` Brian Foster
0 siblings, 1 reply; 4+ messages in thread
From: Jan Kara @ 2014-06-04 15:10 UTC (permalink / raw
To: Brian Foster; +Cc: Jan Kara, xfs
On Wed 04-06-14 09:35:51, Brian Foster wrote:
> On Wed, Jun 04, 2014 at 11:48:13AM +0200, Jan Kara wrote:
> > Rounding in xfs_alloc_fix_len() is wrong. As the comment states, the
> > result should be a number of a form (k*prod+mod) however due to sign
> > mistake the result is different. As a result allocations on raid arrays
> > could be misaligned in some cases.
> >
> > This also seems to fix occasional assertion failure:
> > XFS_WANT_CORRUPTED_GOTO(rlen <= flen, error0)
> > in xfs_alloc_ag_vextent_size().
>
> Do you happen to have a reproducer for this?
No, IBM triggered this during their testing on powerPC. I can ask them if
they can share the test if you are interested.
> The meaning of args->prod (the structure definition comment calls it the
> prod value) is not clear to me. I see that we set it to an extent
> size hint if one exists (in xfs_bmap_btalloc()), so I'll go with that.
> args->mod then becomes the modulo of the file offset against that
> alignment hint.
>
> > Signed-off-by: Jan Kara <jack@suse.cz>
> > ---
> > fs/xfs/xfs_alloc.c | 14 ++++++--------
> > 1 file changed, 6 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/xfs/xfs_alloc.c b/fs/xfs/xfs_alloc.c
> > index c1cf6a336a72..6a0281b16451 100644
> > --- a/fs/xfs/xfs_alloc.c
> > +++ b/fs/xfs/xfs_alloc.c
> > @@ -257,14 +257,12 @@ xfs_alloc_fix_len(
>
> We get here and take the extent length, mod against the alignment and
> compare to the mod of the offset.
>
> > k = rlen % args->prod;
> > if (k == args->mod)
> > return;
> > - if (k > args->mod) {
> > - if ((int)(rlen = rlen - k - args->mod) < (int)args->minlen)
> > - return;
> > - } else {
> > - if ((int)(rlen = rlen - args->prod - (args->mod - k)) <
> > - (int)args->minlen)
> > - return;
> > - }
> > + if (k > args->mod)
> > + rlen = rlen - (k - args->mod);
>
> If the length mod is greater than the offset mod, reduce the length by
> the delta of the mods.
>
> > + else
> > + rlen = rlen - args->prod + (args->mod - k);
>
> Otherwise (length mod is less than offset mod), reduce by a full
> alignment size and add back the difference to match the offset mod.
>
> This seems correct to me.
>
> > + if ((int)rlen < (int)args->minlen)
> > + return;
> > ASSERT(rlen >= args->minlen);
> > ASSERT(rlen <= args->maxlen);
>
> The rlen >= minlen assert seems kind of pointless here, but what about
> changing both instances of these two asserts to the following:
Well, rlen has been decreased so rlen >= minlen makes sense. rlen <=
maxlen seems to be the obvious one to me.
> ASSERT(rlen >= args->minlen && rlen <= args->maxlen);
>
> ... and add a new one after the length adjustment along the lines of:
>
> ASSERT((rlen % args->prod) == args->mod);
>
> Thoughts? Would this have caught the problem you've found earlier?
Yes, this would have caught the bug. Should I add this assertion an
resend?
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
_______________________________________________
xfs mailing list
xfs@oss.sgi.com
http://oss.sgi.com/mailman/listinfo/xfs
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] xfs: Fix rounding in xfs_alloc_fix_len()
2014-06-04 15:10 ` Jan Kara
@ 2014-06-04 15:54 ` Brian Foster
0 siblings, 0 replies; 4+ messages in thread
From: Brian Foster @ 2014-06-04 15:54 UTC (permalink / raw
To: Jan Kara; +Cc: xfs
On Wed, Jun 04, 2014 at 05:10:34PM +0200, Jan Kara wrote:
> On Wed 04-06-14 09:35:51, Brian Foster wrote:
> > On Wed, Jun 04, 2014 at 11:48:13AM +0200, Jan Kara wrote:
> > > Rounding in xfs_alloc_fix_len() is wrong. As the comment states, the
> > > result should be a number of a form (k*prod+mod) however due to sign
> > > mistake the result is different. As a result allocations on raid arrays
> > > could be misaligned in some cases.
> > >
> > > This also seems to fix occasional assertion failure:
> > > XFS_WANT_CORRUPTED_GOTO(rlen <= flen, error0)
> > > in xfs_alloc_ag_vextent_size().
> >
> > Do you happen to have a reproducer for this?
> No, IBM triggered this during their testing on powerPC. I can ask them if
> they can share the test if you are interested.
>
I think it would be generally interesting, particularly to see if we
could create an xfstests test..?
> > The meaning of args->prod (the structure definition comment calls it the
> > prod value) is not clear to me. I see that we set it to an extent
> > size hint if one exists (in xfs_bmap_btalloc()), so I'll go with that.
> > args->mod then becomes the modulo of the file offset against that
> > alignment hint.
> >
> > > Signed-off-by: Jan Kara <jack@suse.cz>
> > > ---
> > > fs/xfs/xfs_alloc.c | 14 ++++++--------
> > > 1 file changed, 6 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/fs/xfs/xfs_alloc.c b/fs/xfs/xfs_alloc.c
> > > index c1cf6a336a72..6a0281b16451 100644
> > > --- a/fs/xfs/xfs_alloc.c
> > > +++ b/fs/xfs/xfs_alloc.c
> > > @@ -257,14 +257,12 @@ xfs_alloc_fix_len(
> >
> > We get here and take the extent length, mod against the alignment and
> > compare to the mod of the offset.
> >
> > > k = rlen % args->prod;
> > > if (k == args->mod)
> > > return;
> > > - if (k > args->mod) {
> > > - if ((int)(rlen = rlen - k - args->mod) < (int)args->minlen)
> > > - return;
> > > - } else {
> > > - if ((int)(rlen = rlen - args->prod - (args->mod - k)) <
> > > - (int)args->minlen)
> > > - return;
> > > - }
> > > + if (k > args->mod)
> > > + rlen = rlen - (k - args->mod);
> >
> > If the length mod is greater than the offset mod, reduce the length by
> > the delta of the mods.
> >
> > > + else
> > > + rlen = rlen - args->prod + (args->mod - k);
> >
> > Otherwise (length mod is less than offset mod), reduce by a full
> > alignment size and add back the difference to match the offset mod.
> >
> > This seems correct to me.
> >
> > > + if ((int)rlen < (int)args->minlen)
> > > + return;
> > > ASSERT(rlen >= args->minlen);
> > > ASSERT(rlen <= args->maxlen);
> >
> > The rlen >= minlen assert seems kind of pointless here, but what about
> > changing both instances of these two asserts to the following:
> Well, rlen has been decreased so rlen >= minlen makes sense. rlen <=
> maxlen seems to be the obvious one to me.
>
That was more a commentary on the fact that the assert now immediately
follows a check for the negation of the assert, where we return. The
assert below seems a bit more generic and just makes it stand out a
little less (to me). Not really a big deal.
> > ASSERT(rlen >= args->minlen && rlen <= args->maxlen);
> >
> > ... and add a new one after the length adjustment along the lines of:
> >
> > ASSERT((rlen % args->prod) == args->mod);
> >
> > Thoughts? Would this have caught the problem you've found earlier?
> Yes, this would have caught the bug. Should I add this assertion an
> resend?
Yeah, if you don't mind. I think that one is definitely beneficial.
Brian
>
> Honza
>
> --
> Jan Kara <jack@suse.cz>
> SUSE Labs, CR
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http://oss.sgi.com/mailman/listinfo/xfs
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2014-06-04 9:48 [PATCH] xfs: Fix rounding in xfs_alloc_fix_len() Jan Kara
2014-06-04 13:35 ` Brian Foster
2014-06-04 15:10 ` Jan Kara
2014-06-04 15:54 ` Brian Foster
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