| Message ID | 20200930063532.142256-2-david@fromorbit.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | xfs: a couple of small fixes | expand |
On Wed, Sep 30, 2020 at 04:35:31PM +1000, Dave Chinner wrote: > From: Dave Chinner <dchinner@redhat.com> > > There are 8 quota stats exposed, but: > > $ grep qm /proc/fs/xfs/stat > qm 0 0 0 1889 308893 0 0 0 0 > $ > > There are 9 values exposed. Code inspection reveals that the struct > xfsstats has a hole in the structure where the values change from 32 > bit counters to 64 bit counters. pahole output: > > .... > uint32_t xs_qm_dquot; /* 748 4 */ > uint32_t xs_qm_dquot_unused; /* 752 4 */ > > /* XXX 4 bytes hole, try to pack */ > > uint64_t xs_xstrat_bytes; /* 760 8 */ Any chance we could use BUILD_BUG_ON(offsetof(xs_xstrat_bytes) % 8 == 0) to catch this kind of thing on 64-bit machines in the future? Or maybe we shift the u64 values to the start of the structure to avoid padding holes? Also, does 32-bit XFS have this 9th value? --D > .... > > Fix this by defining an "end of 32 bit variables" variable that > we then use to define the end of the quota line. This will then > ensure that we print the correct number of values regardless of > structure layout. > > However, ABI requirements for userspace parsers mean we cannot > remove the output that results from this hole, so we also need to > explicitly define this unused value until such time that we actually > add a new stat that makes the output meaningful. > > And now we have a defined end of 32bit variables, update the stats > union to be sized to match all the 32 bit variables correctly. > > Output with this patch: > > $ grep qm /proc/fs/xfs/stat > qm 0 0 0 326 1802 0 6 3 0 > $ > > Reported-by: Nathan Scott <nathans@redhat.com> > Signed-off-by: Dave Chinner <dchinner@redhat.com> > --- > fs/xfs/xfs_stats.c | 2 +- > fs/xfs/xfs_stats.h | 15 +++++++++++++-- > 2 files changed, 14 insertions(+), 3 deletions(-) > > diff --git a/fs/xfs/xfs_stats.c b/fs/xfs/xfs_stats.c > index f70f1255220b..3409b273f00a 100644 > --- a/fs/xfs/xfs_stats.c > +++ b/fs/xfs/xfs_stats.c > @@ -51,7 +51,7 @@ int xfs_stats_format(struct xfsstats __percpu *stats, char *buf) > { "rmapbt", xfsstats_offset(xs_refcbt_2) }, > { "refcntbt", xfsstats_offset(xs_qm_dqreclaims)}, > /* we print both series of quota information together */ > - { "qm", xfsstats_offset(xs_xstrat_bytes)}, > + { "qm", xfsstats_offset(xs_end_of_32bit_counts)}, > }; > > /* Loop over all stats groups */ > diff --git a/fs/xfs/xfs_stats.h b/fs/xfs/xfs_stats.h > index 34d704f703d2..861acf84cb3c 100644 > --- a/fs/xfs/xfs_stats.h > +++ b/fs/xfs/xfs_stats.h > @@ -133,6 +133,17 @@ struct __xfsstats { > uint32_t xs_qm_dqwants; > uint32_t xs_qm_dquot; > uint32_t xs_qm_dquot_unused; > + uint32_t xs_qm_zero_until_next_stat_is_added; > + > +/* > + * Define the end of 32 bit counters as a 32 bit variable so that we don't > + * end up exposing an implicit structure padding hole due to the next counters > + * being 64bit values. If the number of coutners is odd, this fills the hole. If > + * the number of coutners is even the hole is after this variable and the stats > + * line will terminate printing at this offset and not print the hole. > + */ > + uint32_t xs_end_of_32bit_counts; > + > /* Extra precision counters */ > uint64_t xs_xstrat_bytes; > uint64_t xs_write_bytes; > @@ -143,8 +154,8 @@ struct __xfsstats { > > struct xfsstats { > union { > - struct __xfsstats s; > - uint32_t a[xfsstats_offset(xs_qm_dquot)]; > + struct __xfsstats s; > + uint32_t a[xfsstats_offset(xs_end_of_32bit_counts)]; > }; > }; > > -- > 2.28.0 >
On 9/30/20 9:25 AM, Darrick J. Wong wrote: > On Wed, Sep 30, 2020 at 04:35:31PM +1000, Dave Chinner wrote: >> From: Dave Chinner <dchinner@redhat.com> >> >> There are 8 quota stats exposed, but: >> >> $ grep qm /proc/fs/xfs/stat >> qm 0 0 0 1889 308893 0 0 0 0 >> $ >> >> There are 9 values exposed. Code inspection reveals that the struct >> xfsstats has a hole in the structure where the values change from 32 >> bit counters to 64 bit counters. pahole output: >> >> .... >> uint32_t xs_qm_dquot; /* 748 4 */ >> uint32_t xs_qm_dquot_unused; /* 752 4 */ >> >> /* XXX 4 bytes hole, try to pack */ >> >> uint64_t xs_xstrat_bytes; /* 760 8 */ > > Any chance we could use BUILD_BUG_ON(offsetof(xs_xstrat_bytes) % 8 == 0) > to catch this kind of thing on 64-bit machines in the future? Or maybe > we shift the u64 values to the start of the structure to avoid padding > holes? Hmm seems like another case of "add more nice things?" killed off the bugfix. > Also, does 32-bit XFS have this 9th value? on my pi it does ;) # grep qm /proc/fs/xfs/stat qm 0 0 0 0 0 0 0 0 0 > --D > >> .... >> >> Fix this by defining an "end of 32 bit variables" variable that >> we then use to define the end of the quota line. This will then >> ensure that we print the correct number of values regardless of >> structure layout. >> >> However, ABI requirements for userspace parsers mean we cannot >> remove the output that results from this hole, so we also need to >> explicitly define this unused value until such time that we actually >> add a new stat that makes the output meaningful. >> >> And now we have a defined end of 32bit variables, update the stats >> union to be sized to match all the 32 bit variables correctly. >> >> Output with this patch: >> >> $ grep qm /proc/fs/xfs/stat >> qm 0 0 0 326 1802 0 6 3 0 >> $ >> >> Reported-by: Nathan Scott <nathans@redhat.com> >> Signed-off-by: Dave Chinner <dchinner@redhat.com> >> --- >> fs/xfs/xfs_stats.c | 2 +- >> fs/xfs/xfs_stats.h | 15 +++++++++++++-- >> 2 files changed, 14 insertions(+), 3 deletions(-) >> >> diff --git a/fs/xfs/xfs_stats.c b/fs/xfs/xfs_stats.c >> index f70f1255220b..3409b273f00a 100644 >> --- a/fs/xfs/xfs_stats.c >> +++ b/fs/xfs/xfs_stats.c >> @@ -51,7 +51,7 @@ int xfs_stats_format(struct xfsstats __percpu *stats, char *buf) >> { "rmapbt", xfsstats_offset(xs_refcbt_2) }, >> { "refcntbt", xfsstats_offset(xs_qm_dqreclaims)}, >> /* we print both series of quota information together */ >> - { "qm", xfsstats_offset(xs_xstrat_bytes)}, >> + { "qm", xfsstats_offset(xs_end_of_32bit_counts)}, >> }; >> >> /* Loop over all stats groups */ >> diff --git a/fs/xfs/xfs_stats.h b/fs/xfs/xfs_stats.h >> index 34d704f703d2..861acf84cb3c 100644 >> --- a/fs/xfs/xfs_stats.h >> +++ b/fs/xfs/xfs_stats.h >> @@ -133,6 +133,17 @@ struct __xfsstats { >> uint32_t xs_qm_dqwants; >> uint32_t xs_qm_dquot; >> uint32_t xs_qm_dquot_unused; >> + uint32_t xs_qm_zero_until_next_stat_is_added; >> + >> +/* >> + * Define the end of 32 bit counters as a 32 bit variable so that we don't >> + * end up exposing an implicit structure padding hole due to the next counters >> + * being 64bit values. If the number of coutners is odd, this fills the hole. If >> + * the number of coutners is even the hole is after this variable and the stats >> + * line will terminate printing at this offset and not print the hole. >> + */ >> + uint32_t xs_end_of_32bit_counts; >> + >> /* Extra precision counters */ >> uint64_t xs_xstrat_bytes; >> uint64_t xs_write_bytes; >> @@ -143,8 +154,8 @@ struct __xfsstats { >> >> struct xfsstats { >> union { >> - struct __xfsstats s; >> - uint32_t a[xfsstats_offset(xs_qm_dquot)]; >> + struct __xfsstats s; >> + uint32_t a[xfsstats_offset(xs_end_of_32bit_counts)]; >> }; >> }; >> >> -- >> 2.28.0 >> >
On 9/30/20 1:35 AM, Dave Chinner wrote: > From: Dave Chinner <dchinner@redhat.com> > > There are 8 quota stats exposed, but: > > $ grep qm /proc/fs/xfs/stat > qm 0 0 0 1889 308893 0 0 0 0 > $ > > There are 9 values exposed. Code inspection reveals that the struct > xfsstats has a hole in the structure where the values change from 32 > bit counters to 64 bit counters. pahole output: > > .... > uint32_t xs_qm_dquot; /* 748 4 */ > uint32_t xs_qm_dquot_unused; /* 752 4 */ > > /* XXX 4 bytes hole, try to pack */ > > uint64_t xs_xstrat_bytes; /* 760 8 */ > .... > > Fix this by defining an "end of 32 bit variables" variable that > we then use to define the end of the quota line. This will then > ensure that we print the correct number of values regardless of > structure layout. > > However, ABI requirements for userspace parsers mean we cannot > remove the output that results from this hole, so we also need to > explicitly define this unused value until such time that we actually > add a new stat that makes the output meaningful. > > And now we have a defined end of 32bit variables, update the stats > union to be sized to match all the 32 bit variables correctly. > > Output with this patch: > > $ grep qm /proc/fs/xfs/stat > qm 0 0 0 326 1802 0 6 3 0 > $ > > Reported-by: Nathan Scott <nathans@redhat.com> > Signed-off-by: Dave Chinner <dchinner@redhat.com> This makes sense, and fixes a real bug, so seems like it could get merged: Reviewed-by: Eric Sandeen <sandeen@redhat.com> Now, I could bikeshed by suggesting that we avoid holes by doing something like: static const struct xstats_entry { char *desc; int last; } xstats[] = { { "extent_alloc", xfsstats_last(xs_freeb) }, { "abt", xfsstats_last(xs_abt_insrec) }, ... #define xfsstats_last(f) ((offsetof(struct __xfsstats, f)+sizeof(f))/sizeof(uint32_t)) etc, so that we point to the last group item, instead of pointing to the next group's first item, possibly exposing a hole in between. but maybe that's just rearranging deck chairs, and I don't have a very strong opinion on this. -Eric > --- > fs/xfs/xfs_stats.c | 2 +- > fs/xfs/xfs_stats.h | 15 +++++++++++++-- > 2 files changed, 14 insertions(+), 3 deletions(-) > > diff --git a/fs/xfs/xfs_stats.c b/fs/xfs/xfs_stats.c > index f70f1255220b..3409b273f00a 100644 > --- a/fs/xfs/xfs_stats.c > +++ b/fs/xfs/xfs_stats.c > @@ -51,7 +51,7 @@ int xfs_stats_format(struct xfsstats __percpu *stats, char *buf) > { "rmapbt", xfsstats_offset(xs_refcbt_2) }, > { "refcntbt", xfsstats_offset(xs_qm_dqreclaims)}, > /* we print both series of quota information together */ > - { "qm", xfsstats_offset(xs_xstrat_bytes)}, > + { "qm", xfsstats_offset(xs_end_of_32bit_counts)}, > }; > > /* Loop over all stats groups */ > diff --git a/fs/xfs/xfs_stats.h b/fs/xfs/xfs_stats.h > index 34d704f703d2..861acf84cb3c 100644 > --- a/fs/xfs/xfs_stats.h > +++ b/fs/xfs/xfs_stats.h > @@ -133,6 +133,17 @@ struct __xfsstats { > uint32_t xs_qm_dqwants; > uint32_t xs_qm_dquot; > uint32_t xs_qm_dquot_unused; > + uint32_t xs_qm_zero_until_next_stat_is_added; > + > +/* > + * Define the end of 32 bit counters as a 32 bit variable so that we don't > + * end up exposing an implicit structure padding hole due to the next counters > + * being 64bit values. If the number of coutners is odd, this fills the hole. If > + * the number of coutners is even the hole is after this variable and the stats > + * line will terminate printing at this offset and not print the hole. > + */ > + uint32_t xs_end_of_32bit_counts; > + > /* Extra precision counters */ > uint64_t xs_xstrat_bytes; > uint64_t xs_write_bytes; > @@ -143,8 +154,8 @@ struct __xfsstats { > > struct xfsstats { > union { > - struct __xfsstats s; > - uint32_t a[xfsstats_offset(xs_qm_dquot)]; > + struct __xfsstats s; > + uint32_t a[xfsstats_offset(xs_end_of_32bit_counts)]; > }; > }; > >
diff --git a/fs/xfs/xfs_stats.c b/fs/xfs/xfs_stats.c index f70f1255220b..3409b273f00a 100644 --- a/fs/xfs/xfs_stats.c +++ b/fs/xfs/xfs_stats.c @@ -51,7 +51,7 @@ int xfs_stats_format(struct xfsstats __percpu *stats, char *buf) { "rmapbt", xfsstats_offset(xs_refcbt_2) }, { "refcntbt", xfsstats_offset(xs_qm_dqreclaims)}, /* we print both series of quota information together */ - { "qm", xfsstats_offset(xs_xstrat_bytes)}, + { "qm", xfsstats_offset(xs_end_of_32bit_counts)}, }; /* Loop over all stats groups */ diff --git a/fs/xfs/xfs_stats.h b/fs/xfs/xfs_stats.h index 34d704f703d2..861acf84cb3c 100644 --- a/fs/xfs/xfs_stats.h +++ b/fs/xfs/xfs_stats.h @@ -133,6 +133,17 @@ struct __xfsstats { uint32_t xs_qm_dqwants; uint32_t xs_qm_dquot; uint32_t xs_qm_dquot_unused; + uint32_t xs_qm_zero_until_next_stat_is_added; + +/* + * Define the end of 32 bit counters as a 32 bit variable so that we don't + * end up exposing an implicit structure padding hole due to the next counters + * being 64bit values. If the number of coutners is odd, this fills the hole. If + * the number of coutners is even the hole is after this variable and the stats + * line will terminate printing at this offset and not print the hole. + */ + uint32_t xs_end_of_32bit_counts; + /* Extra precision counters */ uint64_t xs_xstrat_bytes; uint64_t xs_write_bytes; @@ -143,8 +154,8 @@ struct __xfsstats { struct xfsstats { union { - struct __xfsstats s; - uint32_t a[xfsstats_offset(xs_qm_dquot)]; + struct __xfsstats s; + uint32_t a[xfsstats_offset(xs_end_of_32bit_counts)]; }; };