On Wed, Feb 19, 2020 at 03:28:47PM +0200, Laurent Pinchart wrote: > Hi Daniel, > > Thank you for the patch. > > On Wed, Feb 19, 2020 at 11:20:33AM +0100, Daniel Vetter wrote: > > We have lots of these. And the cleanup code tends to be of dubious > > quality. The biggest wrong pattern is that developers use devm_, which > > ties the release action to the underlying struct device, whereas > > all the userspace visible stuff attached to a drm_device can long > > outlive that one (e.g. after a hotunplug while userspace has open > > files and mmap'ed buffers). Give people what they want, but with more > > correctness. > > > > Mostly copied from devres.c, with types adjusted to fit drm_device and > > a few simplifications - I didn't (yet) copy over everything. Since > > the types don't match code sharing looked like a hopeless endeavour. > > > > For now it's only super simplified, no groups, you can't remove > > actions (but kfree exists, we'll need that soon). Plus all specific to > > drm_device ofc, including the logging. Which I didn't bother to make > > compile-time optional, since none of the other drm logging is compile > > time optional either. > > > > One tricky bit here is the chicken&egg between allocating your > > drm_device structure and initiliazing it with drm_dev_init. For > > perfect onion unwinding we'd need to have the action to kfree the > > allocation registered before drm_dev_init registers any of its own > > release handlers. But drm_dev_init doesn't know where exactly the > > drm_device is emebedded into the overall structure, and by the time it > > returns it'll all be too late. And forcing drivers to be able clean up > > everything except the one kzalloc is silly. > > > > Work around this by having a very special final_kfree pointer. This > > also avoids troubles with the list head possibly disappearing from > > underneath us when we release all resources attached to the > > drm_device. > > This is all a very good idea ! Many subsystems are plagged by drivers > using devm_k*alloc to allocate data accessible by userspace. Since the > introduction of devm_*, we've likely reduced the number of memory leaks, > but I'm pretty sure we've increased the risk of crashes as I've seen > some drivers that used .release() callbacks correctly being naively > converted to incorrect devm_* usage :-( > > This leads me to a question: if other subsystems have the same problem, > could we turn this implementation into something more generic ? It > doesn't have to be done right away and shouldn't block merging this > series, but I think it would be very useful. It shouldn't be that hard to tie this into a drv_m() type of a thing (driver_memory?) And yes, I think it's much better than devm_* for the obvious reasons of this being needed here. thanks, greg k-h _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
