On Tue, Aug 2, 2022 at 11:06 AM Hans Verkuil <hverkuil-cisco@xxxxxxxxx> wrote: > On 8/2/22 10:42, Andy Shevchenko wrote: > > On Mon, Aug 1, 2022 at 8:35 PM Hans Verkuil <hverkuil-cisco@xxxxxxxxx> wrote: > >> On 01/08/2022 16:57, Andy Shevchenko wrote: > >>> On Mon, Aug 1, 2022 at 3:07 PM Erling Ljunggren (hljunggr) > >>> <hljunggr@xxxxxxxxx> wrote: > >>>> On Fri, 2022-07-29 at 17:51 +0200, Andy Shevchenko wrote: > >>>>> On Thu, Jul 28, 2022 at 1:53 PM Erling Ljunggren <hljunggr@xxxxxxxxx> > >>>>> wrote: ... > >>>>>> + state = kzalloc(sizeof(*state), GFP_KERNEL); > >>>>>> + if (!state) > >>>>>> + return -ENOMEM; > >>>>> > >>>>> devm_kzalloc() ? > >>>> > >>>> This will fail if the device is forcibly unloaded while some > >>>> application has the device node open. > >>> > >>> I'm not sure how it's related. Can you elaborate a bit, please? > >>> > >>> If you try to forcibly unload the device (driver) when it's open and > >>> it somehow succeeds, that will be a sign of lifetime issues in the > >>> code. > >> > >> Not with rmmod but using the unbind facility. > > > > And what is the difference? The device driver core calls the same, no? > > rmmod when the /dev/videoX is open won't work (device is busy), whereas > unbind *will* work, and it is really the same as a USB unplug. Seems there are no guards against that. > >> For new media drivers we generally > >> want to avoid using devm_*alloc, it causes more problems than it solves. > > > > I think it's because people don't think much about the lifetime of > > objects. I don't think devm is an issue here. > > Yes, it is: unbind will call the driver remove() function, and after that > function all memory allocated with devm_*alloc will be freed immediately. Yes. > But if an application still has a filehandle open and was possibly even in > the middle of an ioctl call, then having the memory removed instantaneously > is a really bad thing. True. > Hotpluggable devices in general definitely should not use it. I'm not a fan > of devm_*alloc anymore. You are blaming the wrong man here, i.e. devm. The problem as I stated above is developers who do not understand (pay attention to) the lifetime of the objects. -- With Best Regards, Andy Shevchenko
