Date: Mon, 26 Jan 2026 23:54:57 +0000
From: Matthew Wilcox <willy@infradead.org>
To: Joanne Koong <joannelkoong@gmail.com>
Cc: brauner@kernel.org, hch@infradead.org, djwong@kernel.org,
	bfoster@redhat.com, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v5 1/1] iomap: fix invalid folio access after
 folio_end_read()
Message-ID: <aXf-0c8uLowOW8NQ@casper.infradead.org>
References: <20260126224107.2182262-1-joannelkoong@gmail.com>
 <20260126224107.2182262-2-joannelkoong@gmail.com>
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In-Reply-To: <20260126224107.2182262-2-joannelkoong@gmail.com>

On Mon, Jan 26, 2026 at 02:41:07PM -0800, Joanne Koong wrote:
> If the folio does not have an iomap_folio_state (ifs) attached and the
> folio gets read in by the filesystem's IO helper, folio_end_read() will
> be called by the IO helper at any time. For this case, we cannot access
> the folio after dispatching it to the IO helper, eg subsequent accesses
> like
> 
>         if (ctx->cur_folio &&
>                     offset_in_folio(ctx->cur_folio, iter->pos) == 0) {
> 
> are incorrect.
> 
> Fix these invalid accesses by invalidating ctx->cur_folio if all bytes
> of the folio have been read in by the IO helper.
> 
> This allows us to also remove the +1 bias added for the ifs case. The
> bias was previously added to ensure that if all bytes are read in, the
> IO helper does not end the read on the folio until iomap has decremented
> the bias.
> 
> Fixes: b2f35ac4146d ("iomap: add caller-provided callbacks for read and readahead")
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>