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Date:   Thu, 27 Oct 2022 17:22:03 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Stephen Boyd <sboyd@kernel.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Felipe Balbi <balbi@kernel.org>,
        Johan Hovold <johan@kernel.org>,
        Mathias Nyman <mathias.nyman@linux.intel.com>,
        Kai-Heng Feng <kai.heng.feng@canonical.com>,
        Matthias Kaehlcke <mka@chromium.org>,
        Michael Grzeschik <m.grzeschik@pengutronix.de>,
        Bhuvanesh Surachari <Bhuvanesh_Surachari@mentor.com>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        linux-usb@vger.kernel.org
Subject: Re: [RFC][PATCH v2 20/31] timers: usb: Use del_timer_shutdown()
 before freeing timer
Message-ID: <20221027172203.052a2154@gandalf.local.home>
In-Reply-To: <20221027164227.40225b1f@gandalf.local.home>
References: <20221027150525.753064657@goodmis.org>
        <20221027150928.983388020@goodmis.org>
        <Y1rsO2GeGReS0BvU@rowland.harvard.edu>
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On Thu, 27 Oct 2022 16:42:27 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Thu, 27 Oct 2022 16:38:19 -0400
> Alan Stern <stern@rowland.harvard.edu> wrote:
> 
> > On Thu, Oct 27, 2022 at 11:05:45AM -0400, Steven Rostedt wrote:  
> > > From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> > > 
> > > Before a timer is freed, del_timer_shutdown() must be called.    
> > 
> > Is this supposed to be true for all timers?  Because the USB subsystem 
> > contains an awful lot more timers than just the two you touched in this 
> > patch.  
> 
> Yes, and this does mean that we are going to have to painstakingly find and
> fix ever one of them. This is why the last patch updates
> DEBUG_OBJECTS_TIMERS to detect cases where I miss.

BTW, as del_timer_shutdown() prevents the timer from being re-armed, there
are lots of timers in the kernel where I did not touch, because I could not
tell if the del_timer_sync() or the buggy del_timer() calls were for it to
be freed, or for some other legitimate reason, and I just stayed well enough
alone.

-- Steve