I've learned why it's safe to call __folio_mark_dirty() from mark_buffer_dirty() without holding the folio lock, so update the description to explain why. Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> --- mm/page-writeback.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 62f28fe26511..bd91d5761e39 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -2706,11 +2706,15 @@ void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb) * If warn is true, then emit a warning if the folio is not uptodate and has * not been truncated. * - * The caller must hold folio_memcg_lock(). Most callers have the folio - * locked. A few have the folio blocked from truncation through other - * means (eg zap_vma_pages() 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. + * The caller must hold folio_memcg_lock(). It is the caller's + * responsibility to prevent the folio from being truncated while + * this function is in progress, although it may have been truncated + * before this function is called. Most callers have the folio locked. + * A few have the folio blocked from truncation through other means (e.g. + * zap_vma_pages() has it mapped and is holding the page table lock). + * When called from mark_buffer_dirty(), the filesystem should hold a + * reference to the buffer_head that is being marked dirty, which causes + * try_to_free_buffers() to fail. */ void __folio_mark_dirty(struct folio *folio, struct address_space *mapping, int warn) -- 2.43.0
