linux-kernel - Re: [PATCH RESEND] fs/netfs/read_collect: add to next->prev

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Message-ID: <Z9WJfyaaF1s_eJg_@eldamar.lan>
Date: Sat, 15 Mar 2025 15:06:55 +0100
From: Salvatore Bonaccorso <carnil@...ian.org>
To: Max Kellermann <max.kellermann@...os.com>
Cc: dhowells@...hat.com, netfs@...ts.linux.dev,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH RESEND] fs/netfs/read_collect: add to next->prev_donated

Hi,

On Thu, Feb 20, 2025 at 04:24:50PM +0100, Max Kellermann wrote:
> If multiple subrequests donate data to the same "next" request
> (depending on the subrequest completion order), each of them would
> overwrite the `prev_donated` field, causing data corruption and a
> BUG() crash ("Can't donate prior to front").
> 
> Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
> Closes: https://lore.kernel.org/netfs/CAKPOu+_4mUwYgQtRTbXCmi+-k3PGvLysnPadkmHOyB7Gz0iSMA@mail.gmail.com/
> Cc: stable@...r.kernel.org
> Signed-off-by: Max Kellermann <max.kellermann@...os.com>
> Signed-off-by: David Howells <dhowells@...hat.com>
> ---
>  fs/netfs/read_collect.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c
> index 8878b46589ff..cafadfe8e858 100644
> --- a/fs/netfs/read_collect.c
> +++ b/fs/netfs/read_collect.c
> @@ -284,7 +284,7 @@ static bool netfs_consume_read_data(struct netfs_io_subrequest *subreq, bool was
>  				   netfs_trace_donate_to_deferred_next);
>  	} else {
>  		next = list_next_entry(subreq, rreq_link);
> -		WRITE_ONCE(next->prev_donated, excess);
> +		WRITE_ONCE(next->prev_donated, next->prev_donated + excess);
>  		trace_netfs_donate(rreq, subreq, next, excess,
>  				   netfs_trace_donate_to_next);
>  	}
> -- 
> 2.47.2

Unless I did some mistakes researching both the stable, netfs lists,
did this felt through the cracks and is still missing for to be picked
for the 6.12.y and 6.13.y series?

Regards,
Salvatore