for_each_perag_wrap() doesn't expect 0 as 2nd arg.
To iterate all the available AGs, just use for_each_perag() instead.
Signed-off-by: Ryosuke Yasuoka <[email protected]>
---
fs/xfs/xfs_filestream.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/xfs/xfs_filestream.c b/fs/xfs/xfs_filestream.c
index 22c13933c8f8..48f43c340c58 100644
--- a/fs/xfs/xfs_filestream.c
+++ b/fs/xfs/xfs_filestream.c
@@ -151,7 +151,7 @@ xfs_filestream_pick_ag(
* grab.
*/
if (!max_pag) {
- for_each_perag_wrap(args->mp, 0, start_agno, args->pag)
+ for_each_perag(args->mp, start_agno, args->pag)
break;
atomic_inc(&args->pag->pagf_fstrms);
*longest = 0;
--
2.39.2
On 4/4/23 3:47 AM, Ryosuke Yasuoka wrote:
> for_each_perag_wrap() doesn't expect 0 as 2nd arg.
> To iterate all the available AGs, just use for_each_perag() instead.
Can you explain what goes wrong if it is zero? Is there a test for this?
If it's a general problem, what if the other 2 callers pass in the variable
start_agno with a value of 0?
(I may well be missing something obvious as those macros are a bit dense)
Thanks,
-Eric
> Signed-off-by: Ryosuke Yasuoka <[email protected]>
> ---
> fs/xfs/xfs_filestream.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/xfs/xfs_filestream.c b/fs/xfs/xfs_filestream.c
> index 22c13933c8f8..48f43c340c58 100644
> --- a/fs/xfs/xfs_filestream.c
> +++ b/fs/xfs/xfs_filestream.c
> @@ -151,7 +151,7 @@ xfs_filestream_pick_ag(
> * grab.
> */
> if (!max_pag) {
> - for_each_perag_wrap(args->mp, 0, start_agno, args->pag)
> + for_each_perag(args->mp, start_agno, args->pag)
> break;
> atomic_inc(&args->pag->pagf_fstrms);
> *longest = 0;
On Tue, Apr 04, 2023 at 05:47:01PM +0900, Ryosuke Yasuoka wrote:
> for_each_perag_wrap() doesn't expect 0 as 2nd arg.
> To iterate all the available AGs, just use for_each_perag() instead.
Thanks, Ryosuke-san. IIUC, this is a fix for the recent sysbot
reported filestreams oops regression?
Can you include the context of the failure it reported (i.e. the
trace from the oops), and the 'reported-by' tag for the syzbot
report?
It should probably also include a 'Fixes: bd4f5d09cc93 ("xfs:
refactor the filestreams allocator pick functions")' tag as well.
> Signed-off-by: Ryosuke Yasuoka <[email protected]>
> ---
> fs/xfs/xfs_filestream.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/xfs/xfs_filestream.c b/fs/xfs/xfs_filestream.c
> index 22c13933c8f8..48f43c340c58 100644
> --- a/fs/xfs/xfs_filestream.c
> +++ b/fs/xfs/xfs_filestream.c
> @@ -151,7 +151,7 @@ xfs_filestream_pick_ag(
> * grab.
> */
> if (!max_pag) {
> - for_each_perag_wrap(args->mp, 0, start_agno, args->pag)
> + for_each_perag(args->mp, start_agno, args->pag)
> break;
While this will definitely avoid the oops, I don't think it is quite
right. If we want to iterate all AGs, then we should be starting the
iteration at AG 0, not start_agno. i.e.
+ for_each_perag(args->mp, 0, args->pag)
Cheers,
Dave.
--
Dave Chinner
[email protected]
On Wed, Apr 05, 2023 at 05:04:14PM +0900, Ryosuke Yasuoka wrote:
> Dave,
>
> Thank you for reviewing my requests.
>
> > > for_each_perag_wrap() doesn't expect 0 as 2nd arg.
> > > To iterate all the available AGs, just use for_each_perag() instead.
> >
> > Thanks, Ryosuke-san. IIUC, this is a fix for the recent sysbot
> > reported filestreams oops regression?
> >
> > Can you include the context of the failure it reported (i.e. the
> > trace from the oops), and the 'reported-by' tag for the syzbot
> > report?
> >
> > It should probably also include a 'Fixes: bd4f5d09cc93 ("xfs:
> > refactor the filestreams allocator pick functions")' tag as well.
>
> No. my request is in the same code area where syzbot bug was reported,
> but it might not be relevant. A kernel applying my patch got the same Oops.
>
> I'm indeed checking the syzbot's bug and I realized that this small bug fix
> is not related to it based on my tests. Thus I sent the patch
> as a separate one.
>
> > While this will definitely avoid the oops, I don't think it is quite
> > right. If we want to iterate all AGs, then we should be starting the
> > iteration at AG 0, not start_agno. i.e.
> >
> > + for_each_perag(args->mp, 0, args->pag)
>
> I agree with your proposal because it is more direct.
> However, as the current for_each_perag() macro always assigns 0 to (agno),
> it will cause compilation errors.
Yup, I didn't compile test my suggestion - i just quickly wrote it
down to demonstrate what I was thinking. I expect that you have
understood that using for_each_perag() was what I was suggesting is
used, not that the sample code I wrote is exactly correct. IOWs,
for_each_perag(args->mp, start_agno, args->pag)
would have worked, even though the code does not do what it looks
like it should from the context of start_agno. Which means this
would be better:
start_agno = 0;
for_each_perag_from(args->mp, start_agno, args->pag)
because it directly documents the value we are iterating from.
> Although I haven't checked other callers deeply, we should modify
> the macro as follows:
>
> #define for_each_perag(mp, agno, pag) \
> - (agno) = 0; \
> for_each_perag_from((mp), (agno), (pag))
That is not correct, either. agno needs to be a variable - it is
the loop agno counter that tracks the iteration.
Cheers,
Dave.
--
Dave Chinner
[email protected]
Eric,
I failed to reply to you since I got some mistakes.
Let me re-send my reply just in case.
Thank you for reviewing my requests.
> Can you explain what goes wrong if it is zero? Is there a test for this?
>
> If it's a general problem, what if the other 2 callers pass in the variable
> start_agno with a value of 0?
Sorry I couldn't prepare any tests to confirm what happens if it is zero
because it is a kind of general problem.
IIUC, passing zero to for_each_perag_wrap() is not problematic.
As the comment describes, this macro iterates all AG from start_agno through
wrap_agno, then wrap to restart_agno, and then iterates again toward to
start_agno - 1. It looks like some issue occurs when start_agno is zero.
However, for_each_perag_wrap() actually won't wrap if start_agno is zero.
static inline struct xfs_perag *
xfs_perag_next_wrap(
struct xfs_perag *pag,
xfs_agnumber_t *agno,
xfs_agnumber_t stop_agno,
xfs_agnumber_t restart_agno,
xfs_agnumber_t wrap_agno)
{
struct xfs_mount *mp = pag->pag_mount;
*agno = pag->pag_agno + 1;
xfs_perag_rele(pag);
while (*agno != stop_agno) {
if (*agno >= wrap_agno) {
if (restart_agno >= stop_agno) <<<--- HERE
break;
*agno = restart_agno;
}
pag = xfs_perag_grab(mp, *agno);
if (pag)
return pag;
(*agno)++;
}
return NULL;
}
/*
* Iterate all AGs from start_agno through wrap_agno, then restart_agno through
* (start_agno - 1).
*/
#define for_each_perag_wrap_range(mp, start_agno, restart_agno,
wrap_agno, agno, pag) \
for ((agno) = (start_agno), (pag) = xfs_perag_grab((mp), (agno)); \
(pag) != NULL; \
(pag) = xfs_perag_next_wrap((pag), &(agno), (start_agno), \
(restart_agno), (wrap_agno)))
...
#define for_each_perag_wrap_at(mp, start_agno, wrap_agno, agno, pag) \
for_each_perag_wrap_range((mp), (start_agno), 0, (wrap_agno), (agno), (pag))
...
#define for_each_perag_wrap(mp, start_agno, agno, pag) \
for_each_perag_wrap_at((mp), (start_agno), (mp)->m_sb.sb_agcount, \
(agno), (pag))
OTOH, since we have already a for_each_perag() macro, which just iterates all AG
from 0 and doesn't wrap, I think it is simpler to use for_earch_perag().
Regards,
Ryosuke
Dave,
> On Thu, Apr 6, 2023 at 8:04 AM Dave Chinner <[email protected]> wrote:
> >
> > On Wed, Apr 05, 2023 at 05:04:14PM +0900, Ryosuke Yasuoka wrote:
> > > Dave,
> > >
> > > Thank you for reviewing my requests.
> > >
> > > > > for_each_perag_wrap() doesn't expect 0 as 2nd arg.
> > > > > To iterate all the available AGs, just use for_each_perag() instead.
> > > >
> > > > Thanks, Ryosuke-san. IIUC, this is a fix for the recent sysbot
> > > > reported filestreams oops regression?
> > > >
> > > > Can you include the context of the failure it reported (i.e. the
> > > > trace from the oops), and the 'reported-by' tag for the syzbot
> > > > report?
> > > >
> > > > It should probably also include a 'Fixes: bd4f5d09cc93 ("xfs:
> > > > refactor the filestreams allocator pick functions")' tag as well.
> > >
> > > No. my request is in the same code area where syzbot bug was reported,
> > > but it might not be relevant. A kernel applying my patch got the same Oops.
> > >
> > > I'm indeed checking the syzbot's bug and I realized that this small bug fix
> > > is not related to it based on my tests. Thus I sent the patch
> > > as a separate one.
> > >
> > > > While this will definitely avoid the oops, I don't think it is quite
> > > > right. If we want to iterate all AGs, then we should be starting the
> > > > iteration at AG 0, not start_agno. i.e.
> > > >
> > > > + for_each_perag(args->mp, 0, args->pag)
> > >
> > > I agree with your proposal because it is more direct.
> > > However, as the current for_each_perag() macro always assigns 0 to (agno),
> > > it will cause compilation errors.
> >
> > Yup, I didn't compile test my suggestion - i just quickly wrote it
> > down to demonstrate what I was thinking. I expect that you have
> > understood that using for_each_perag() was what I was suggesting is
> > used, not that the sample code I wrote is exactly correct. IOWs,
> >
> > for_each_perag(args->mp, start_agno, args->pag)
> >
> > would have worked, even though the code does not do what it looks
> > like it should from the context of start_agno. Which means this
> > would be better:
> >
> > start_agno = 0;
> > for_each_perag_from(args->mp, start_agno, args->pag)
> >
> > because it directly documents the value we are iterating from.
OK. I'll update my patch, run a compile test, and then send again as a
v2 another thread
Thank you for reviewing.
Ryosuke
On 4/6/23 11:03 AM, Ryosuke Yasuoka wrote:
> Eric,
>
> I failed to reply to you since I got some mistakes.
> Let me re-send my reply just in case.
>
> Thank you for reviewing my requests.
>
>> Can you explain what goes wrong if it is zero? Is there a test for this?
>>
>> If it's a general problem, what if the other 2 callers pass in the variable
>> start_agno with a value of 0?
> Sorry I couldn't prepare any tests to confirm what happens if it is zero
> because it is a kind of general problem.
>
> IIUC, passing zero to for_each_perag_wrap() is not problematic.
...
> OTOH, since we have already a for_each_perag() macro, which just iterates all AG
> from 0 and doesn't wrap, I think it is simpler to use for_earch_perag().
>
> Regards,
> Ryosuke
Ok - I couldn't tell from the original email if this was a bugfix or a
cleanup, and wanted to be sure.
Thanks!
-Eric