linux-kernel - Re: [PATCH] rpmsg: char: Avoid double destroy of default endpoint

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Date:   Tue, 20 Sep 2022 18:18:27 +0200
From:   Arnaud POULIQUEN <arnaud.pouliquen@...s.st.com>
To:     Shengjiu Wang <shengjiu.wang@....com>,
        <mathieu.poirier@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>
CC:     <linux-remoteproc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <shengjiu.wang@...il.com>
Subject: Re: [PATCH] rpmsg: char: Avoid double destroy of default endpoint

Hello Shengjiu,

On 9/16/22 08:39, Shengjiu Wang wrote:
> The rpmsg_dev_remove() in rpmsg_core is the place for releasing
> this default endpoint.
> 
> So need to avoid destroying the default endpoint in
> rpmsg_chrdev_eptdev_destroy(), this should be the same as
> rpmsg_eptdev_release(). Otherwise there will be double destroy
> issue that ept->refcount report warning:
> 
> refcount_t: underflow; use-after-free.
> 
> Call trace:
>  refcount_warn_saturate+0xf8/0x150
>  virtio_rpmsg_destroy_ept+0xd4/0xec
>  rpmsg_dev_remove+0x60/0x70
> 
> Fixes: bea9b79c2d10 ("rpmsg: char: Add possibility to use default endpoint of the rpmsg device")
> Signed-off-by: Shengjiu Wang <shengjiu.wang@....com>
> ---
>  drivers/rpmsg/rpmsg_char.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> index 0850ae34fb88..562d545ac0d3 100644
> --- a/drivers/rpmsg/rpmsg_char.c
> +++ b/drivers/rpmsg/rpmsg_char.c
> @@ -76,7 +76,8 @@ int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
>  
>  	mutex_lock(&eptdev->ept_lock);
>  	if (eptdev->ept) {
> -		rpmsg_destroy_ept(eptdev->ept);
> +		if (!eptdev->default_ept)
> +			rpmsg_destroy_ept(eptdev->ept);
>  		eptdev->ept = NULL;
>  	}
>  	mutex_unlock(&eptdev->ept_lock);


Good catch!
I tried to reproduce it but without success. Do you set a specific config?

Concerning the patch:

Could you add a comment, to help to understand the condition?
something like "The default endpoint is released by the rpmsg core"

With that Reviewed-by: Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>

Thanks,
Arnaud