linux-kernel - Re: [RFC][PATCH 1/8] epoll: remove epmutex from ep_free() & eventpoll_release

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Message-ID: <20171028135854.mpdcngbkozssucrs@linux-n805>
Date:   Sat, 28 Oct 2017 06:58:54 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Hou Tao <houtao1@...wei.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        viro@...iv.linux.org.uk, jbaron@...mai.com, oleg@...hat.com,
        koct9i@...il.com
Subject: Re: [RFC][PATCH 1/8] epoll: remove epmutex from ep_free() &
 eventpoll_release_file()

On Sat, 28 Oct 2017, Hou Tao wrote:

>Remove the global epmutex from ep_free() and eventpoll_release_file().
>In the later patches, we will add locks with a smaller granularity
>to serve the same purposes of epmutex.
>
>Signed-off-by: Hou Tao <houtao1@...wei.com>
>---
> fs/eventpoll.c | 4 ----
> 1 file changed, 4 deletions(-)
>
>diff --git a/fs/eventpoll.c b/fs/eventpoll.c
>index 2fabd19..26ab0c5 100644
>--- a/fs/eventpoll.c
>+++ b/fs/eventpoll.c
>@@ -835,7 +835,6 @@ static void ep_free(struct eventpoll *ep)
> 	 * anymore. The only hit might come from eventpoll_release_file() but
> 	 * holding "epmutex" is sufficient here.
> 	 */
^^
What about this comment (and the equivalent one in eventpoll_release_file()?

>-	mutex_lock(&epmutex);

...even if you fix it in a later patch, this patch breaks bisection. Now
we just race between ep_free() and eventpoll_release_file(). This patch
should be folded in, no?

Thanks,
Davidlohr