From:   Giuseppe Scrivano <gscrivan@redhat.com>
To:     Rik van Riel <riel@surriel.com>
Cc:     viro@zeniv.linux.org.uk, linux-kernel@vger.kernel.org,
        kernel-team@meta.com, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3 0/2] ipc,namespace: fix free vs allocation race
In-Reply-To: <20230127184651.3681682-1-riel@surriel.com> (Rik van Riel's
        message of "Fri, 27 Jan 2023 13:46:49 -0500")
References: <20230127184651.3681682-1-riel@surriel.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux)
Date:   Fri, 27 Jan 2023 19:56:27 +0100
Message-ID: <87wn57lsbo.fsf@redhat.com>
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Rik van Riel <riel@surriel.com> writes:

> The IPC namespace code frees ipc_namespace structures asynchronously,
> via a work queue item. This results in ipc_namespace structures being
> freed very slowly, and the allocation path getting false failures
> since the to-be-freed ipc_namespace structures have not been freed
> yet.
>
> Fix that by having the allocator wait when there are ipc_namespace
> structures pending to be freed.
>
> Also speed up the freeing of ipc_namespace structures. We had some
> discussions about this last year, and ended up trying out various
> "nicer" ideas that did not work, so I went back to the original,
> with Al Viro's suggestion for a helper function:
>
> https://lore.kernel.org/all/Yg8StKzTWh+7FLuA@zeniv-ca.linux.org.uk/
>
> This series fixes both the false allocation failures, and the slow
> freeing of ipc_namespace structures.
>
> v3: remove mq_put_mnt (thank you Giuseppe)
> v2: a few more fs/namespace.c cleanups suggested by Al Viro (thank you!)

Tested-by: Giuseppe Scrivano <gscrivan@redhat.com>