netdev - Re: [RFC PATCH] iwlwifi: iwl-dbg: Use del_timer

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Date:   Fri, 8 Apr 2022 05:20:18 +0000
From:   "Coelho, Luciano" <luciano.coelho@...el.com>
To:     "linux@...ck-us.net" <linux@...ck-us.net>,
        "Greenman, Gregory" <gregory.greenman@...el.com>
CC:     "kvalo@...nel.org" <kvalo@...nel.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "Berg, Johannes" <johannes.berg@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [RFC PATCH] iwlwifi: iwl-dbg: Use del_timer_sync() before freeing

On Thu, 2022-04-07 at 12:50 -0700, Guenter Roeck wrote:
> Hi,
> 
> On 4/6/22 08:34, Guenter Roeck wrote:
> > In Chrome OS, a large number of crashes is observed due to corrupted timer
> > lists. Steven Rostedt pointed out that this usually happens when a timer
> > is freed while still active, and that the problem is often triggered
> > by code calling del_timer() instead of del_timer_sync() just before
> > freeing.
> > 
> > Steven also identified the iwlwifi driver as one of the possible culprits
> > since it does exactly that.
> > 
> > Reported-by: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Shahar S Matityahu <shahar.s.matityahu@...el.com>
> > Cc: Johannes Berg <johannes.berg@...el.com>
> > Fixes: 60e8abd9d3e91 ("iwlwifi: dbg_ini: add periodic trigger new API support")
> > Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> > ---
> > RFC:
> >      Maybe there was a reason to use del_timer() instead of del_timer_sync().
> >      Also, I am not sure if the change is sufficient since I don't see any
> >      obvious locking that would prevent timers from being added and then
> >      modified in iwl_dbg_tlv_set_periodic_trigs() while being removed in
> >      iwl_dbg_tlv_del_timers().
> > 
> 
> I prepared a new version of this patch, introducing a mutex to protect changes
> to periodic_trig_list. I'd like to get some feedback before sending it out,
> though, so I'll wait until next week before sending it.
> 
> If you have any feedback/thoughts/comments, please let me know.

Hi Guenter,

Thanks for your proposal!

I recently moved from the Intel WiFi team to the Graphics team, so I'm
adding Gregory, who has taken over my duties, to the discussion.

I don't recall any specific reasons for using del_timer() instead of
del_timer_sync() here.  So your patch does look correct to me.

--
Cheers,
Luca.