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Date: Fri, 15 Aug 2014 16:39:02 +0200 From: Oleg Nesterov <oleg@...hat.com> To: "Luis R. Rodriguez" <mcgrof@...e.com> Cc: "Luis R. Rodriguez" <mcgrof@...not-panic.com>, gregkh@...uxfoundation.org, tiwai@...e.de, linux-kernel@...r.kernel.org, Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>, Joseph Salisbury <joseph.salisbury@...onical.com>, Kay Sievers <kay@...y.org>, One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>, Tim Gardner <tim.gardner@...onical.com>, Pierre Fersing <pierre-fersing@...rref.org>, Andrew Morton <akpm@...ux-foundation.org>, Benjamin Poirier <bpoirier@...e.de>, Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>, Praveen Krishnamoorthy <praveen.krishnamoorthy@...gotech.com>, Sreekanth Reddy <sreekanth.reddy@...gotech.com>, Abhijit Mahajan <abhijit.mahajan@...gotech.com>, Hariprasad S <hariprasad@...lsio.com>, Santosh Rastapur <santosh@...lsio.com>, MPT-FusionLinux.pdl@...gotech.com, linux-scsi@...r.kernel.org, netdev@...r.kernel.org Subject: Re: [PATCH v3 1/3] init / kthread: add module_long_probe_init() and module_long_probe_exit() On 08/15, Luis R. Rodriguez wrote: > > On Wed, Aug 13, 2014 at 07:51:01PM +0200, Oleg Nesterov wrote: > > On 08/12, Luis R. Rodriguez wrote: > > > > > > +/* To be used by modules which can take over 30 seconds at probe */ > > > > Probably the comment should explain that this hack should only be > > used if the driver is buggy and is wating for "real fix". > > > > > +#define module_long_probe_init(initfn) \ > > > + static struct task_struct *__init_thread; \ > > > + static int _long_probe_##initfn(void *arg) \ > > > + { \ > > > + return initfn(); \ > > > + } \ > > > + static inline __init int __long_probe_##initfn(void) \ > > > + { \ > > > + __init_thread = kthread_run(_long_probe_##initfn,\ > > > + NULL, \ > > > + #initfn); \ > > > + if (IS_ERR(__init_thread)) \ > > > + return PTR_ERR(__init_thread); \ > > > + return 0; \ > > > + } \ > > > + module_init(__long_probe_##initfn); > > > +/* To be used by modules that require module_long_probe_init() */ > > > +#define module_long_probe_exit(exitfn) \ > > > + static inline void __long_probe_##exitfn(void) \ > > > + { \ > > > + exitfn(); \ > > > + if (__init_thread) \ > > > + kthread_stop(__init_thread); \ > > > + } \ > > > > exitfn() should be called after kthread_stop(), and only if initfn() > > returns 0. So it should probably do > > > > int err = kthread_stop(__init_thread); > > if (!err) > > exitfn(); > > Thanks! With the check for __init_thread as well as it can be > ERR_PTR(-ENOMEM), ERR_PTR(-EINTR), or NULL (for whatever other > reason). Do you mean __long_probe_##exitfn() should also check ERR_PTR(__init_thread)? I don't think so. If kthread_run() above fails, module_init() should return the error (it does), so module_exit() won't be called. > > But there is an additional complication, you can't use __init_thread > > without get_task_struct(), > > Can you elaborate why ? kthread_stop() uses get_task_struct(), This is too late. This task_struct can be already freed/reused. See below. > wake_up_process() and finally put_task_struct(), and we're the > only user of this thread. Also kthread_run() ensures wake_up_process() > gets called on startup, so not sure where the race would be provided > all users here and with the respective helpers on buggy drivers. > > > so __long_probe_##initfn() can't use > > kthread_run(). It needs kthread_create() + get_task_struct() + wakeup. > > I fail to see why we'd need to add get_task_struct() on > module_long_probe_init(), can you clarify? kthread_stop(kthread_run(callback)) is only safe if callback() can not exit on its own, without checking kthread_should_stop(). And btw that is why kthread_stop() does get_task_struct()). If callback() can exit (if it calls do_exit() or simply returns), then nothing protects this task_struct, it will be freed. Oleg. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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