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Sender: Guenter Roeck <groeck7@gmail.com>
Message-ID: <5b361192-6fd4-e84d-d6fc-e552a473c23e@roeck-us.net>
Date:   Thu, 7 Apr 2022 12:50:25 -0700
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Subject: Re: [RFC PATCH] iwlwifi: iwl-dbg: Use del_timer_sync() before freeing
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To:     Luca Coelho <luciano.coelho@intel.com>
Cc:     Kalle Valo <kvalo@kernel.org>, linux-wireless@vger.kernel.org,
        netdev@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>,
        Johannes Berg <johannes.berg@intel.com>
References: <20220406153410.1899768-1-linux@roeck-us.net>
From:   Guenter Roeck <linux@roeck-us.net>
In-Reply-To: <20220406153410.1899768-1-linux@roeck-us.net>
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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@goodmis.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Shahar S Matityahu <shahar.s.matityahu@intel.com>
> Cc: Johannes Berg <johannes.berg@intel.com>
> Fixes: 60e8abd9d3e91 ("iwlwifi: dbg_ini: add periodic trigger new API support")
> Signed-off-by: Guenter Roeck <linux@roeck-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.

Thanks,
Guenter

>   drivers/net/wireless/intel/iwlwifi/iwl-dbg-tlv.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/intel/iwlwifi/iwl-dbg-tlv.c b/drivers/net/wireless/intel/iwlwifi/iwl-dbg-tlv.c
> index 866a33f49915..3237d4b528b5 100644
> --- a/drivers/net/wireless/intel/iwlwifi/iwl-dbg-tlv.c
> +++ b/drivers/net/wireless/intel/iwlwifi/iwl-dbg-tlv.c
> @@ -371,7 +371,7 @@ void iwl_dbg_tlv_del_timers(struct iwl_trans *trans)
>   	struct iwl_dbg_tlv_timer_node *node, *tmp;
>   
>   	list_for_each_entry_safe(node, tmp, timer_list, list) {
> -		del_timer(&node->timer);
> +		del_timer_sync(&node->timer);
>   		list_del(&node->list);
>   		kfree(node);
>   	}