Re: [PATCH v2] fs/buffer: serialize set_buffer_uptodate against concurrent clears

[Matthew Wilcox <willy@infradead.org>]

On Thu, Jul 30, 2026 at 06:09:24PM -0400, Chris S wrote:
> Yes, that works. And appreciate your reply.
>   I prototyped it, and it survives a journal replay.
> 
> Six sites, with bio_add_virt_nofail() covering the submit side:
> 
>   bh_offset()                     b_page may be NULL
>   buffer_set_crypto_ctx()         NULL guard
>   __bh_submit()                   bio_add_virt_nofail() when !b_folio, and
>                                   skip wbc_account_cgroup_owner()
>   jbd2_journal_write_metadata_buffer()
>                                   b_folio = NULL, b_data =
>                                   jh->b_frozen_data, not folio_set_bh()
>   jbd2_checksum_data(), jbd2_block_tag_csum_set()   both kmap the temp bh
>                                   (fs/jbd2/commit.c:705 and :745)
> 
> 4 files, +38/-12.  I'll send it as the first patch of the series.

Fantastic.  Would you care to also include this patch as part of your
series?

From f7cd3419ce0518ba429ac854282888833bf60147 Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Date: Thu, 30 Jul 2026 20:43:22 -0400
Subject: [PATCH] buffer_head: Remove b_page

All users except bh_offset() have been converted to use b_folio instead.
Convert bh_offset() and remove b_page.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/buffer_head.h | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 8b23bc9a244c..3881141a3ff1 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -59,10 +59,7 @@ struct address_space;
 struct buffer_head {
 	unsigned long b_state;		/* buffer state bitmap (see above) */
 	struct buffer_head *b_this_page;/* circular list of page's buffers */
-	union {
-		struct page *b_page;	/* the page this bh is mapped to */
-		struct folio *b_folio;	/* the folio this bh is mapped to */
-	};
+	struct folio *b_folio;		/* the folio this bh is mapped to */
 
 	sector_t b_blocknr;		/* start block number */
 	size_t b_size;			/* size of mapping */
@@ -172,7 +169,7 @@ static __always_inline int buffer_uptodate(const struct buffer_head *bh)
 
 static inline unsigned long bh_offset(const struct buffer_head *bh)
 {
-	return (unsigned long)(bh)->b_data & (page_size(bh->b_page) - 1);
+	return (unsigned long)(bh)->b_data & (folio_size(bh->b_folio) - 1);
 }
 
 /* If we *know* page->private refers to buffer_heads */
-- 
2.47.3