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xfs: fix transaction block reservation in xrep_rtbitmap

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LOLLM pointed out an inconsistency in the block reservation code in
xrep_rtbitmap.  The first is that the reservation computation is not
consistent between the code that sets up the repair and the code that
tries to avoid exceeding the transaction reservation once we know how
big the rtbitmap really must be.  As a result, the logic doesn't work.

In fixing that, a second problem emerges: if we do readjust, we ask for
the entire reservation all over again.  We really only need the delta,
so ask only for that.

Fix all these problems by hoisting the computation to a trivial helper
so that it gets used in both places.

Cc: stable@vger.kernel.org # v6.14
Fixes: 8defee8dff ("xfs: online repair of realtime bitmaps for a realtime group")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
This commit is contained in:
Darrick J. Wong
2026-07-20 20:24:02 -07:00
committed by Carlos Maiolino
parent 270ffcd9b0
commit 61606f8846
1 changed files with 28 additions and 18 deletions
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46
fs/xfs/scrub/rtbitmap_repair.c
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@@ -36,6 +36,24 @@
/* rt bitmap content repairs */
/*
* Reserve enough blocks to write out a completely new bitmap file, plus twice
* as many blocks as we would need if we can only allocate one block per data
* fork mapping. This should cover the preallocation of the temporary file and
* exchanging the extent mappings.
*
* We cannot use xfs_exchmaps_estimate because we have not yet constructed the
* replacement bitmap and therefore do not know how many extents it will use.
* By the time we do, we will have a dirty transaction (which we cannot drop
* because we cannot drop the rtbitmap ILOCK) and cannot ask for more
* reservation.
*/
static inline unsigned long long
xrep_rtbitmap_calc_blocks(struct xfs_mount *mp, unsigned long long blocks)
{
return blocks + (xfs_bmbt_calc_size(mp, blocks) * 2);
}
/* Set up to repair the realtime bitmap for this group. */
int
xrep_setup_rtbitmap(
@@ -56,20 +74,7 @@ xrep_setup_rtbitmap(
if (error)
return error;
/*
* Reserve enough blocks to write out a completely new bitmap file,
* plus twice as many blocks as we would need if we can only allocate
* one block per data fork mapping. This should cover the
* preallocation of the temporary file and exchanging the extent
* mappings.
*
* We cannot use xfs_exchmaps_estimate because we have not yet
* constructed the replacement bitmap and therefore do not know how
* many extents it will use. By the time we do, we will have a dirty
* transaction (which we cannot drop because we cannot drop the
* rtbitmap ILOCK) and cannot ask for more reservation.
*/
blocks += xfs_bmbt_calc_size(mp, blocks) * 2;
blocks = xrep_rtbitmap_calc_blocks(mp, mp->m_sb.sb_rbmblocks);
if (blocks > UINT_MAX)
return -EOPNOTSUPP;
@@ -512,7 +517,7 @@ xrep_rtbitmap(
struct xchk_rtbitmap *rtb = sc->buf;
struct xfs_mount *mp = sc->mp;
struct xfs_group *xg = rtg_group(sc->sr.rtg);
unsigned long long blocks = 0;
unsigned long long blocks;
unsigned int busy_gen;
int error;
@@ -532,15 +537,20 @@ xrep_rtbitmap(
* figure out if we need to adjust the block reservation in the
* transaction.
*/
blocks = xfs_bmbt_calc_size(mp, rtb->rbmblocks);
blocks = xrep_rtbitmap_calc_blocks(mp, rtb->rbmblocks);
if (blocks > UINT_MAX)
return -EOPNOTSUPP;
if (blocks > rtb->resblks) {
error = xfs_trans_reserve_more(sc->tp, blocks, 0);
uint64_t delta = blocks - rtb->resblks;
if (delta > UINT_MAX)
return -EOPNOTSUPP;
error = xfs_trans_reserve_more(sc->tp, delta, 0);
if (error)
return error;
rtb->resblks += blocks;
rtb->resblks += delta;
}
/* Fix inode core and forks. */