linux-kernel - Re: [RFC PATCH 1/1] iomap: fix race between iomap_set_range_uptodate and folio_end

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Message-ID: <aYvzUihKhMfM6agz@casper.infradead.org>
Date: Wed, 11 Feb 2026 03:11:14 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Joanne Koong <joannelkoong@...il.com>
Cc: Wei Gao <wegao@...e.com>, Sasha Levin <sashal@...nel.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/1] iomap: fix race between iomap_set_range_uptodate
 and folio_end_read

On Tue, Feb 10, 2026 at 02:18:06PM -0800, Joanne Koong wrote:
>                 spin_lock_irqsave(&ifs->state_lock, flags);
> -               uptodate = ifs_set_range_uptodate(folio, ifs, off, len);
> +               /*
> +                * If a read is in progress, we must NOT call
> folio_mark_uptodate.
> +                * The read completion path (iomap_finish_folio_read or
> +                * iomap_read_end) will call folio_end_read() which uses XOR
> +                * semantics to set the uptodate bit. If we set it here, the XOR
> +                * in folio_end_read() will clear it, leaving the folio not
> +                * uptodate.
> +                */
> +               uptodate = ifs_set_range_uptodate(folio, ifs, off, len) &&
> +                       !ifs->read_bytes_pending;
>                 spin_unlock_irqrestore(&ifs->state_lock, flags);

This can't possibly be the right fix.  There's some horrible confusion
here.  It should not be possible to have read bytes pending _and_ the
entire folio be uptodate.  That's an invariant that should always be
maintained.