linux-kernel - Re: [PATCH 1/2] xen: privcmd: Switch from mutex to spinlock for irqfds

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Message-ID: <17aa46c3-89e9-40aa-bb15-817230712f07@suse.com>
Date: Tue, 2 Jul 2024 12:12:45 +0200
From: Juergen Gross <jgross@...e.com>
To: Viresh Kumar <viresh.kumar@...aro.org>,
 Stefano Stabellini <sstabellini@...nel.org>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>,
 Alex Bennée <alex.bennee@...aro.org>,
 Manos Pitsidianakis <manos.pitsidianakis@...aro.org>,
 Paolo Bonzini <pbonzini@...hat.com>, Al Viro <viro@...iv.linux.org.uk>,
 xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] xen: privcmd: Switch from mutex to spinlock for
 irqfds

On 18.06.24 11:42, Viresh Kumar wrote:
> irqfd_wakeup() gets EPOLLHUP, when it is called by
> eventfd_release() by way of wake_up_poll(&ctx->wqh, EPOLLHUP), which
> gets called under spin_lock_irqsave(). We can't use a mutex here as it
> will lead to a deadlock.
> 
> Fix it by switching over to a spin lock.
> 
> Reported-by: Al Viro <viro@...iv.linux.org.uk>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>   drivers/xen/privcmd.c | 26 +++++++++++++++-----------
>   1 file changed, 15 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 67dfa4778864..5ceb6c56cf3e 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -13,7 +13,6 @@
>   #include <linux/file.h>
>   #include <linux/kernel.h>
>   #include <linux/module.h>
> -#include <linux/mutex.h>

I don't think you can drop that. There is still the ioreq_lock mutex.

I can fix that up while committing, with that:

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen

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