On Wed, Jul 19, 2017 at 09:20:22AM -0400, Brian Foster wrote:
> On Tue, Jul 18, 2017 at 11:24:22AM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >
> > We must initialize the firstfsb parameter to _bmapi_write so that it
> > doesn't incorrectly treat stack garbage as a restriction on which AGs
> > it can search for free space.
> >
> > Fixes-coverity-id: 1402025
> > Fixes-coverity-id: 1415167
> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > ---
> > fs/xfs/libxfs/xfs_bmap.c | 2 +-
> > fs/xfs/xfs_reflink.c | 2 +-
> > 2 files changed, 2 insertions(+), 2 deletions(-)
> >
> >
> > diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> > index 935adde..8c4ee60 100644
> > --- a/fs/xfs/libxfs/xfs_bmap.c
> > +++ b/fs/xfs/libxfs/xfs_bmap.c
> > @@ -6508,7 +6508,7 @@ xfs_bmap_finish_one(
> > xfs_filblks_t *blockcount,
> > xfs_exntst_t state)
> > {
> > - xfs_fsblock_t firstfsb;
> > + xfs_fsblock_t firstfsb = NULLFSBLOCK;
> > int error = 0;
> >
>
> Shouldn't firstfsb be tied to the transaction lifetime in (at least)
> this case? It is used in the allocator to control things like AG locking
> order.
That is correct...
> Here, it looks like we could potentially do multiple unmaps in a
> single transaction without carrying the firstfsb state across..?
...but keep in mind that we call xfs_bmap_finish_one once per
transaction and roll transactions until the work is done. I'll add a
comment here to that effect:
/*
* firstfsb is tied to the transaction lifetime and is used to ensure
* correct AG locking order and schedule work item continuations.
* XFS_BUI_MAX_FAST_EXTENTS (== 1) restricts us to only making one bmap
* call per transaction, so it should be safe as a local variable.
*/
> FWIW this patch still looks fine either way:
>
> Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
Thank you for the review!
--D
>
> > trace_xfs_bmap_deferred(tp->t_mountp,
> > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> > index ab2270a..d9b3d57 100644
> > --- a/fs/xfs/xfs_reflink.c
> > +++ b/fs/xfs/xfs_reflink.c
> > @@ -329,7 +329,7 @@ xfs_reflink_convert_cow_extent(
> > xfs_filblks_t count_fsb,
> > struct xfs_defer_ops *dfops)
> > {
> > - xfs_fsblock_t first_block;
> > + xfs_fsblock_t first_block = NULLFSBLOCK;
> > int nimaps = 1;
> >
> > if (imap->br_state == XFS_EXT_NORM)
> >
> > --
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