Sender: Larry Finger <larry.finger@gmail.com>
Message-ID: <93bc48d2-a692-3709-e323-929600f37646@lwfinger.net>
Date:   Thu, 23 Feb 2023 17:09:35 -0600
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From:   Larry Finger <Larry.Finger@lwfinger.net>
Subject: Re: [PATCH] wifi: wext: Eliminate log spamming in
 wireless_warn_cfg80211_wext()
To:     Johannes Berg <johannes@sipsolutions.net>,
        Kalle Valo <kvalo@kernel.org>
Cc:     linux-wireless@vger.kernel.org
References: <20230222204945.6716-1-Larry.Finger@lwfinger.net>
 <2564165999cf5319e58aa0898a2866612f8af293.camel@sipsolutions.net>
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On 2/23/23 02:12, Johannes Berg wrote:
> On Wed, 2023-02-22 at 14:49 -0600, Larry Finger wrote:
>> Commit dc09766c755c {"wifi: wireless: warn on most wireless extension
>> usage") introduces a warning when wireless extensions are used with
>> cfg80211 drivers. Although such a warning is desirable, the current
>> implementation overflows the dmesg buffer with thousands of warnings,
>> all of which are the same.
>>
> 
> What are you seeing them from?
> 
> This is rate-limited, so not sure why you're getting so many?
> 
>>   A WARN_ONCE() call is sufficient.
> 
> I think a WARN is inappropriate (it's a userspace 'issue', not an in-
> kernel consistency problem), but I guess we could pr_once().
> 
> But that's not great because it only shows a single application that was
> still using it, not if there are multiple.
> 
> Hmm. Not sure what to do. Let's start with "why are you getting it so
> much". Maybe we can somehow print it less, or try to do per application
> once, or something.

Johannes,

This patch has a magic number, but it does the job:

diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
index 13a72b17248e..22a67172a163 100644
--- a/net/wireless/wext-core.c
+++ b/net/wireless/wext-core.c
@@ -637,12 +637,27 @@ void wireless_send_event(struct net_device *      dev,
  EXPORT_SYMBOL(wireless_send_event);

  #ifdef CONFIG_CFG80211_WEXT
+
+#define ARRAY_MAX  15
+static char name_array[ARRAY_MAX][TASK_COMM_LEN];
+static int array_count = 0;
+
  static void wireless_warn_cfg80211_wext(void)
  {
         char name[sizeof(current->comm)];
+       int i;

-       pr_warn_ratelimited("warning: `%s' uses wireless extensions that are 
deprecated for modern drivers; use nl80211\n",
-                           get_task_comm(name, current));
+       get_task_comm(name, current);
+       for (i = 0; i < array_count; i++) {
+               if (!strncmp(name, name_array[i], TASK_COMM_LEN))
+                       return;
+       }
+       /* Found new one - print warning and add to array */
+       strncpy(name_array[array_count], name, TASK_COMM_LEN);
+       if (array_count < ARRAY_MAX)
+               array_count++;
+       pr_warn("warning: `%s' uses wireless extensions that are deprecated for 
modern drivers; use nl80211\n",
+               name);
  }
  #endif

Looking at my log, I do get only one for each application.

finger@localhost:~>dmesg | grep warning | grep nl80211
[    8.826056] warning: `nspr-2' uses wireless extensions that are deprecated 
for modern drivers; use nl80211
[   17.212260] warning: `kded5' uses wireless extensions that are deprecated for 
modern drivers; use nl80211
[   17.252420] warning: `Qt bearer threa' uses wireless extensions that are 
deprecated for modern drivers; use nl80211
[   22.664380] warning: `akonadi_notes_a' uses wireless extensions that are 
deprecated for modern drivers; use nl80211
[   23.058001] warning: `akonadi_maildis' uses wireless extensions that are 
deprecated for modern drivers; use nl80211
[   23.175135] warning: `akonadi_mailmer' uses wireless extensions that are 
deprecated for modern drivers; use nl80211
[   23.329265] warning: `akonadi_followu' uses wireless extensions that are 
deprecated for modern drivers; use nl80211
[   24.075119] warning: `akonadi_sendlat' uses wireless extensions that are 
deprecated for modern drivers; use nl80211

I have no idea why most, if not all, of those applications even care about 
wireless. As you can see, I get 8 messages in a relatively short time, thus I 
selected 15 as the size of the array.

Larry