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

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Message-ID: <20221031201445.GA2977400@roeck-us.net>
Date:   Mon, 31 Oct 2022 13:14:45 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Johan Hovold <johan@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        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, Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        John Stultz <jstultz@...gle.com>
Subject: Re: [RFC][PATCH v2 20/31] timers: usb: Use del_timer_shutdown()
 before freeing timer

On Mon, Oct 31, 2022 at 08:50:58AM -0700, Guenter Roeck wrote:
> On Sun, Oct 30, 2022 at 11:48:28AM -0400, Steven Rostedt wrote:
> > On Sat, 29 Oct 2022 15:56:25 -0700
> > Guenter Roeck <linux@...ck-us.net> wrote:
> > 
> > > >> WARNING: CPU: 0 PID: 9 at lib/debugobjects.c:502 debug_print_object+0xd0/0x100
> > > >> ODEBUG: free active (active state 0) object type: timer_list hint: neigh_timer_handler+0x0/0x480
> > > >>
> > > >> That happens with almost every test, so I may have missed some others
> > > >> in the noise.  
> > > > 
> > > > Can you add this?
> > > >   
> > > 
> > > It doesn't make a difference.
> > 
> > Ah, it also requires this (I have other debugging in that file, so it may
> > only apply with some fuzzing):
> > 
> 
> Almost good, except for the attached backtrace. That seems to happen
> on shutdown after bootting from a usb drive, but not on all platforms.
> 
> The warning is in __mod_timer():
> 
>         if (WARN_ON_ONCE(!timer->function))
>                 return -EINVAL;
> 
> This may be due to the change in blk_sync_queue() which I suspect may
> be called prior to the last mod_timer() call. I'll add some debug code
> to verify.
> 

I see that additional requests are sent to the scsi device after the call
to blk_sync_queue(). The description of this function suggests that this
may happen. Overall it does not seem to be appropriate to call
del_timer_shutdown() from blk_sync_queue(). I'll change my test code
accordingly.

Guenter