Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v13 02/13] eventfd: Export eventfd_wake_count to modules
To:     Xie Yongji <xieyongji@bytedance.com>, mst@redhat.com,
        stefanha@redhat.com, sgarzare@redhat.com, parav@nvidia.com,
        hch@infradead.org, christian.brauner@canonical.com,
        rdunlap@infradead.org, willy@infradead.org,
        viro@zeniv.linux.org.uk, axboe@kernel.dk, bcrl@kvack.org,
        corbet@lwn.net, mika.penttila@nextfour.com,
        dan.carpenter@oracle.com, joro@8bytes.org,
        gregkh@linuxfoundation.org, zhe.he@windriver.com,
        xiaodong.liu@intel.com, joe@perches.com, robin.murphy@arm.com,
        will@kernel.org, john.garry@huawei.com
Cc:     songmuchun@bytedance.com,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        kvm@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
References: <20210831103634.33-1-xieyongji@bytedance.com>
 <20210831103634.33-3-xieyongji@bytedance.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <0e486c0a-0055-e698-ffd2-31c4b75dae5d@redhat.com>
Date:   Wed, 1 Sep 2021 10:50:40 +0800
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0)
 Gecko/20100101 Thunderbird/78.13.0
MIME-Version: 1.0
In-Reply-To: <20210831103634.33-3-xieyongji@bytedance.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Precedence: bulk


在 2021/8/31 下午6:36, Xie Yongji 写道:
> Export eventfd_wake_count so that some modules can use
> the eventfd_signal_count() to check whether the
> eventfd_signal() call should be deferred to a safe context.
>
> Signed-off-by: Xie Yongji <xieyongji@bytedance.com>


And this matches the comment inside eventfd_signal():

         /*
          * Deadlock or stack overflow issues can happen if we recurse here
          * through waitqueue wakeup handlers. If the caller users 
potentially
          * nested waitqueues with custom wakeup handlers, then it should
          * check eventfd_signal_count() before calling this function. If
          * it returns true, the eventfd_signal() call should be 
deferred to a
          * safe context.
          */


So:

Acked-by: Jason Wang <jasowang@redhat.com>


> ---
>   fs/eventfd.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/fs/eventfd.c b/fs/eventfd.c
> index e265b6dd4f34..1b3130b8d6c1 100644
> --- a/fs/eventfd.c
> +++ b/fs/eventfd.c
> @@ -26,6 +26,7 @@
>   #include <linux/uio.h>
>   
>   DEFINE_PER_CPU(int, eventfd_wake_count);
> +EXPORT_PER_CPU_SYMBOL_GPL(eventfd_wake_count);
>   
>   static DEFINE_IDA(eventfd_ida);
>