linux-kernel - Re: [net] 5478fcd0f4: BUG:sleeping_function_called_from_invalid_context_at

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Date:   Mon, 22 Mar 2021 09:05:36 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Antoine Tenart <atenart@...nel.org>
Cc:     kernel test robot <oliver.sang@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexander Duyck <alexander.duyck@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        lkp@...ts.01.org, lkp@...el.com, ltp@...ts.linux.it
Subject: Re: [net]  5478fcd0f4:
 BUG:sleeping_function_called_from_invalid_context_at_include/linux/sched/mm.h

On Mon, Mar 22, 2021 at 09:55:50AM +0100, Antoine Tenart wrote:
> I only had a quick look at this, but I think the issue should be fixed
> with:
> 
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index e16d54aabd4c..3ae3c20eb64c 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -1378,7 +1378,7 @@ static ssize_t xps_queue_show(struct net_device *dev, unsigned int index,
>         nr_ids = dev_maps ? dev_maps->nr_ids :
>                  (type == XPS_CPUS ? nr_cpu_ids : dev->num_rx_queues);
>  
> -       mask = bitmap_zalloc(nr_ids, GFP_KERNEL);
> +       mask = bitmap_zalloc(nr_ids, GFP_ATOMIC);
>         if (!mask) {
>                 rcu_read_unlock();
>                 return -ENOMEM;

sysfs isn't a good reason to use GFP_ATOMIC.

try something like this:

-       mask = bitmap_zalloc(nr_ids, GFP_KERNEL);
+       mask = bitmap_zalloc(nr_ids, GFP_NOWAIT);
        if (!mask) {
+               int new_nr_ids;
+
                rcu_read_unlock();
-               return -ENOMEM;
+               mask = bitmap_zalloc(nr_ids, GFP_KERNEL);
+               if (!mask)
+                       return -ENOMEM;
+               rcu_read_lock();
+               dev_maps = rcu_dereference(dev->xps_maps[type]);
+               /* if nr_ids shrank while we slept, do not overrun array.
+                * if it increased, we just won't show the new ones
+                */
+               new_nr_ids = dev_maps ? dev_maps->nr_ids :
+                       (type == XPS_CPUS ? nr_cpu_ids : dev->num_rx_queues);
+               if (new_nr_ids < nr_ids)
+                       nr_ids = new_nr_ids;