Re: [PATCH] dma-buf: fix locking in sync_print_obj()

From: Chris Wilson <chris@chris-wilson.co.uk>
To: Dan Carpenter <dan.carpenter@oracle.com>,
	Sumit Semwal <sumit.semwal@linaro.org>
Cc: Gustavo Padovan <gustavo.padovan@collabora.com>,
	Sean Paul <seanpaul@chromium.org>,
	linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
	linaro-mm-sig@lists.linaro.org, kernel-janitors@vger.kernel.org
Subject: Re: [PATCH] dma-buf: fix locking in sync_print_obj()
Date: Fri, 24 Jan 2020 10:20:56 +0000	[thread overview]
Message-ID: <157986125623.2524.13979010293671565726@skylake-alporthouse-com> (raw)
In-Reply-To: <20200124101311.drryaegcdc7d4x7e@kili.mountain>

Quoting Dan Carpenter (2020-01-24 10:13:12)
> This is always called with IRQs disabled and we don't actually want to
> enable IRQs at the end.
> 
> Fixes: a6aa8fca4d79 ("dma-buf/sw-sync: Reduce irqsave/irqrestore from known context")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
>  drivers/dma-buf/sync_debug.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma-buf/sync_debug.c b/drivers/dma-buf/sync_debug.c
> index 101394f16930..952331344b1c 100644
> --- a/drivers/dma-buf/sync_debug.c
> +++ b/drivers/dma-buf/sync_debug.c
> @@ -107,15 +107,16 @@ static void sync_print_fence(struct seq_file *s,
>  static void sync_print_obj(struct seq_file *s, struct sync_timeline *obj)
>  {
>         struct list_head *pos;
> +       unsigned long flags;
>  
>         seq_printf(s, "%s: %d\n", obj->name, obj->value);
>  
> -       spin_lock_irq(&obj->lock);
> +       spin_lock_irqsave(&obj->lock, flags);

Exactly, it can be just spin_lock() as the irq state is known.

Once again I question why this [sync_debug.c] code even exists.
-Chris