From: Wenjie Qi Fault-around can map ready dropbehind folios without going through the normal page-cache lookup that clears dropbehind. A mapping represents a competing cached user, so retain the folio instead of forcibly unmapping it when writeback completes. For a mapped folio, folio_unmap_invalidate() can call unmap_mapping_folio(), which takes i_mmap_rwsem and may sleep. Retaining mapped folios avoids this path when folio_end_dropbehind() runs in non-preemptible task context. Unmapped dropbehind folios continue through the existing invalidation path. Fixes: fb7d3bc41493 ("mm/filemap: drop streaming/uncached pages when writeback completes") Signed-off-by: Wenjie Qi Reviewed-by: Matthew Wilcox (Oracle) Reviewed-by: Tal Zussman --- Changes since v2: - Explain why retaining mapped folios avoids a sleepable unmap path. - Add the Fixes and Reviewed-by trailers. mm/filemap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/filemap.c b/mm/filemap.c index 6afec636881f..00fd89cf6f55 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1616,7 +1616,7 @@ static void filemap_end_dropbehind(struct folio *folio) return; if (!folio_test_clear_dropbehind(folio)) return; - if (mapping) + if (mapping && !folio_mapped(folio)) folio_unmap_invalidate(mapping, folio, 0); } -- 2.43.0