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

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Message-ID: <3978045.1739537266@warthog.procyon.org.uk>
Date: Fri, 14 Feb 2025 12:47:46 +0000
From: David Howells <dhowells@...hat.com>
To: Max Kellermann <max.kellermann@...os.com>
Cc: dhowells@...hat.com, netfs@...ts.linux.dev,
    linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: Re: [PATCH] fs/netfs/read_collect: add to next->prev_donated

Max Kellermann <max.kellermann@...os.com> wrote:

> David, this seems to fix the bug for me.  Please also check if we need
> a "donation_changed" check.

Shouldn't do since at that point we've been holding rreq->lock since the last
check.

> 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/
> Signed-off-by: Max Kellermann <max.kellermann@...os.com>

Signed-off-by: David Howells <dhowells@...hat.com>