* If warn is true, then emit a warning if the folio is not uptodate and has
* not been truncated.
*
- * The caller must hold lock_page_memcg().
+ * The caller must hold lock_page_memcg(). Most callers have the folio
+ * locked. A few have the folio blocked from truncation through other
+ * means (eg zap_page_range() has it mapped and is holding the page table
+ * lock). This can also be called from mark_buffer_dirty(), which I
+ * cannot prove is always protected against truncate.
*/
void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,
int warn)