linux-kernel - Re: [RFC][PATCH v2 20/31] timers: usb: Use del_timer

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Date:   Thu, 27 Oct 2022 17:22:03 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Johan Hovold <johan@...nel.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Michael Grzeschik <m.grzeschik@...gutronix.de>,
        Bhuvanesh Surachari <Bhuvanesh_Surachari@...tor.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        linux-usb@...r.kernel.org
Subject: Re: [RFC][PATCH v2 20/31] timers: usb: Use del_timer_shutdown()
 before freeing timer

On Thu, 27 Oct 2022 16:42:27 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Thu, 27 Oct 2022 16:38:19 -0400
> Alan Stern <stern@...land.harvard.edu> wrote:
> 
> > On Thu, Oct 27, 2022 at 11:05:45AM -0400, Steven Rostedt wrote:  
> > > From: "Steven Rostedt (Google)" <rostedt@...dmis.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