On Fri, May 03, 2024 at 10:53:03PM +0100, Al Viro wrote: > On Fri, May 03, 2024 at 02:42:22PM -0700, Linus Torvalds wrote: > > On Fri, 3 May 2024 at 14:36, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > > > > > ... the last part is no-go - poll_wait() must be able to grab a reference > > > (well, the callback in it must) > > > > Yeah. I really think that *poll* itself is doing everything right. It > > knows that it's called with a file pointer with a reference, and it > > adds its own references as needed. > > Not really. Note that select's __pollwait() does *NOT* leave a reference > at the mercy of driver - it's stuck into poll_table_entry->filp and > the poll_freewait() knows how to take those out. > > > dmabuf does something very different - it grabs the damn thing into > its private data structures and for all we know it could keep it for > a few hours, until some even materializes. dma_fence must complete in reasonable amount of time, where "reasonable" is roughly in line with other i/o (including the option that there's timeouts if the hw's gone busted). So definitely not hours (aside from driver bugs when things go really wrong ofc), but more like a few seconds in a worst case scenario. -Sima -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
