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Date: Fri, 18 Sep 2026 15:30:26 +0200
From: Christoph Hellwig <hch@lst.de>
To: Viacheslav Dubeyko <slava@dubeyko.com>
Cc: glaubitz@physik.fu-berlin.de, frank.li@vivo.com, hch@lst.de,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	vdubeyko@coreweave.com, willy@infradead.org, brauner@kernel.org,
	djwong@kernel.org
Subject: Re: [PATCH v4 3/7] hfsplus: take the bitmap page lock for
 allocate/free
Message-ID: <20260918133026.GC18107@lst.de>
References: <20260914233941.2966421-1-slava@dubeyko.com> <20260914233941.2966421-4-slava@dubeyko.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Mon, Sep 14, 2026 at 04:39:37PM -0700, Viacheslav Dubeyko wrote:
> The hfsplus_block_allocate() and hfsplus_block_free() kmap
> the allocation bitmap's pages and modify their bits in place
> under sbi->alloc_mutex, but without holding the page lock.
> That leaves the read-modify-write of the bitmap bits
> unprotected against a concurrent writeback of the same page,
> which can read a partially-updated bitmap word or race with
> the dirty-bit update.

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

> +	lock_page(page);
> +	folio_wait_writeback(page_folio(page));
>  	pptr = kmap_local_page(page);

Although this really begs for a folio conversion rather sooner than
later.