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@zeniv.linux.org.uk 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