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. > >> 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. 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. Hotpluggable devices in general definitely should not use it. I'm not a fan of devm_*alloc anymore. Regards, Hans > >> It's unlikely to be an issue here, but I'd rather keep it as-is. > > OK. >
