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Message-ID: <8fd06532-0ae8-47a7-a4f2-f5b01a25bf93@infradead.org>
Date: Thu, 4 Jan 2024 13:08:44 -0800
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Subject: Re: [PATCH 1/5] doc: Improve the description of __folio_mark_dirty
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To: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
 Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
 linux-kernel@vger.kernel.org
References: <20240104163652.3705753-1-willy@infradead.org>
 <20240104163652.3705753-2-willy@infradead.org>
From: Randy Dunlap <rdunlap@infradead.org>
In-Reply-To: <20240104163652.3705753-2-willy@infradead.org>
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On 1/4/24 08:36, Matthew Wilcox (Oracle) wrote:
> 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@infradead.org>
> ---
>  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 cd4e4ae77c40..96da6716cb86 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2652,11 +2652,15 @@ 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 (eg

preferably s/eg/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)

-- 
#Randy