os/bluestore: In BlueFS::truncate accept wierd alloc_unit

The alignment of extents might not reflect current alloc_unit[bdev].
It might be caused be either fallback to alternate AU size for SLOW,
or change of allocation unit in DB or WAL.
In such cases, truncation just leaves extent untouched.

Fixes: https://tracker.ceph.com/issues/71235

Signed-off-by: Adam Kupczyk <[email protected]>

Author: aclamk

src/os/bluestore/BlueFS.cc

@@ -4224,10 +4224,12 @@ int BlueFS::truncate(FileWriter *h, uint64_t offset)/*_WF_L*/
         changed_extents = true;
         ++p;
       } else {
-        // cut_off > p->length means that we misaligned the extent
-        ceph_assert(cut_off == p->length);
+        // Usually cut_off == p->length.
+        // Case cut_off > p->length means that we misaligned the extent
+        // or alloc size changed in the meantime.
+        // In both cases just leave extent untouched.
         fnode.allocated = (offset - x_off) + p->length;
-        ++p; // leave extent untouched
+        ++p;
       }
       while (p != fnode.extents.end()) {
         dirty.pending_release[p->bdev].insert(p->offset, p->length);