NFSv4/filelayout: Anchor page coalescing on pattern_offset

filelayout_pg_test() bounds page coalescing to a single stripe unit
using an offset relative to pls_range.offset, but the data server is
selected by nfs4_fl_calc_j_index() using an offset relative to
pattern_offset.  When a segment's pattern_offset and range offset are
not congruent modulo the stripe unit, the coalescing window is shifted
off the DS-selection grid, so a coalesced I/O can straddle a stripe
boundary and send the bytes past it to the wrong data server.

Anchor coalescing on pattern_offset to match nfs4_fl_calc_j_index().
Stripe-congruent segments, including the common whole-file pattern_offset
0 case, are unchanged.

Fixes: c6194271f94b ("pnfs: filelayout: support non page aligned layouts")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Benjamin Coddington <bcodding@hammerspace.com>
Signed-off-by: Anna Schumaker <anna.schumaker@hammerspace.com>

0 files changed, 0 insertions, 0 deletions