From: Brian Foster bfoster@redhat.com
commit f74681ba2006434be195402e0b15fc5763cddd7e upstream.
[Slightly modify xfs_trans_alloc() to fix a merge conflict due to missing "atomic_inc(&mp->m_active_trans)" statement in v5.9 kernel]
The rmapbt extent swap algorithm remaps individual extents between the source inode and the target to trigger reverse mapping metadata updates. If either inode straddles a format or other bmap allocation boundary, the individual unmap and map cycles can trigger repeated bmap block allocations and frees as the extent count bounces back and forth across the boundary. While net block usage is bound across the swap operation, this behavior can prematurely exhaust the transaction block reservation because it continuously drains as the transaction rolls. Each allocation accounts against the reservation and each free returns to global free space on transaction roll.
The previous workaround to this problem attempted to detect this boundary condition and provide surplus block reservation to acommodate it. This is insufficient because more remaps can occur than implied by the extent counts; if start offset boundaries are not aligned between the two inodes, for example.
To address this problem more generically and dynamically, add a transaction accounting mode that returns freed blocks to the transaction reservation instead of the superblock counters on transaction roll and use it when the rmapbt based algorithm is active. This allows the chain of remap transactions to preserve the block reservation based own its own frees and prevent premature exhaustion regardless of the remap pattern. Note that this is only safe for superblocks with lazy sb accounting, but the latter is required for v5 supers and the rmap feature depends on v5.
Fixes: b3fed434822d0 ("xfs: account format bouncing into rmapbt swapext tx reservation") Root-caused-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Brian Foster bfoster@redhat.com Reviewed-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Darrick J. Wong darrick.wong@oracle.com Acked-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Chandan Babu R chandan.babu@oracle.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/xfs/libxfs/xfs_shared.h | 1 + fs/xfs/xfs_bmap_util.c | 18 +++++++++--------- fs/xfs/xfs_trans.c | 19 ++++++++++++++++++- 3 files changed, 28 insertions(+), 10 deletions(-)
--- a/fs/xfs/libxfs/xfs_shared.h +++ b/fs/xfs/libxfs/xfs_shared.h @@ -65,6 +65,7 @@ void xfs_log_get_max_trans_res(struct xf #define XFS_TRANS_DQ_DIRTY 0x10 /* at least one dquot in trx dirty */ #define XFS_TRANS_RESERVE 0x20 /* OK to use reserved data blocks */ #define XFS_TRANS_NO_WRITECOUNT 0x40 /* do not elevate SB writecount */ +#define XFS_TRANS_RES_FDBLKS 0x80 /* reserve newly freed blocks */ /* * LOWMODE is used by the allocator to activate the lowspace algorithm - when * free space is running low the extent allocator may choose to allocate an --- a/fs/xfs/xfs_bmap_util.c +++ b/fs/xfs/xfs_bmap_util.c @@ -1740,6 +1740,7 @@ xfs_swap_extents( int lock_flags; uint64_t f; int resblks = 0; + unsigned int flags = 0;
/* * Lock the inodes against other IO, page faults and truncate to @@ -1795,17 +1796,16 @@ xfs_swap_extents( resblks += XFS_SWAP_RMAP_SPACE_RES(mp, tipnext, w);
/* - * Handle the corner case where either inode might straddle the - * btree format boundary. If so, the inode could bounce between - * btree <-> extent format on unmap -> remap cycles, freeing and - * allocating a bmapbt block each time. + * If either inode straddles a bmapbt block allocation boundary, + * the rmapbt algorithm triggers repeated allocs and frees as + * extents are remapped. This can exhaust the block reservation + * prematurely and cause shutdown. Return freed blocks to the + * transaction reservation to counter this behavior. */ - if (ipnext == (XFS_IFORK_MAXEXT(ip, w) + 1)) - resblks += XFS_IFORK_MAXEXT(ip, w); - if (tipnext == (XFS_IFORK_MAXEXT(tip, w) + 1)) - resblks += XFS_IFORK_MAXEXT(tip, w); + flags |= XFS_TRANS_RES_FDBLKS; } - error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0, 0, &tp); + error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0, flags, + &tp); if (error) goto out_unlock;
--- a/fs/xfs/xfs_trans.c +++ b/fs/xfs/xfs_trans.c @@ -107,7 +107,8 @@ xfs_trans_dup(
ntp->t_flags = XFS_TRANS_PERM_LOG_RES | (tp->t_flags & XFS_TRANS_RESERVE) | - (tp->t_flags & XFS_TRANS_NO_WRITECOUNT); + (tp->t_flags & XFS_TRANS_NO_WRITECOUNT) | + (tp->t_flags & XFS_TRANS_RES_FDBLKS); /* We gave our writer reference to the new transaction */ tp->t_flags |= XFS_TRANS_NO_WRITECOUNT; ntp->t_ticket = xfs_log_ticket_get(tp->t_ticket); @@ -273,6 +274,8 @@ xfs_trans_alloc( */ WARN_ON(resp->tr_logres > 0 && mp->m_super->s_writers.frozen == SB_FREEZE_COMPLETE); + ASSERT(!(flags & XFS_TRANS_RES_FDBLKS) || + xfs_sb_version_haslazysbcount(&mp->m_sb)); atomic_inc(&mp->m_active_trans);
tp->t_magic = XFS_TRANS_HEADER_MAGIC; @@ -368,6 +371,20 @@ xfs_trans_mod_sb( tp->t_blk_res_used += (uint)-delta; if (tp->t_blk_res_used > tp->t_blk_res) xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE); + } else if (delta > 0 && (tp->t_flags & XFS_TRANS_RES_FDBLKS)) { + int64_t blkres_delta; + + /* + * Return freed blocks directly to the reservation + * instead of the global pool, being careful not to + * overflow the trans counter. This is used to preserve + * reservation across chains of transaction rolls that + * repeatedly free and allocate blocks. + */ + blkres_delta = min_t(int64_t, delta, + UINT_MAX - tp->t_blk_res); + tp->t_blk_res += blkres_delta; + delta -= blkres_delta; } tp->t_fdblocks_delta += delta; if (xfs_sb_version_haslazysbcount(&mp->m_sb))