On Wed, May 19, 2021 at 11:11:55PM +1000, Alistair Popple wrote: > On Wednesday, 19 May 2021 10:15:41 PM AEST Peter Xu wrote: > > External email: Use caution opening links or attachments > > > > On Wed, May 19, 2021 at 09:04:53PM +1000, Alistair Popple wrote: > > > Failing fork() because we couldn't take a lock doesn't seem like the right > > > approach though, especially as there is already existing code that > > > retries. I get this adds complexity though, so would be happy to take a > > > look at cleaning copy_pte_range() up in future. > > > > Yes, I proposed that as this one won't affect any existing applications > > (unlike the existing ones) but only new userspace driver apps that will use > > this new atomic feature. > > > > IMHO it'll be a pity to add extra complexity and maintainance burden into > > fork() if only for keeping the "logical correctness of fork()" however the > > code never triggers. If we start with trylock we'll know whether people > > will use it, since people will complain with a reason when needed; however > > I still doubt whether a sane userspace device driver should fork() within > > busy interaction with the device underneath.. > > I will refrain from commenting on the sanity or otherwise of doing that :-) > > Agree such a scenario seems unlikely in practice (and possibly unreasonable). > Keeping the "logical correctness of fork()" still seems worthwhile to me, but > if the added complexity/maintenance burden for an admittedly fairly specific > feature is going to stop progress here I am happy to take the fail fork > approach. I could then possibly fix it up as a future clean up to > copy_pte_range(). Perhaps others have thoughts? Yes, it's more about making this series easier to be accepted, and it'll be great to have others' input. Btw, just to mention that I don't even think fail fork() on failed trylock() is against "logical correctness of fork()": IMHO it's still 100% correct just like most syscalls can return with -EAGAIN, that suggests the userspace to try again the syscall, and I hope that also works for fork(). I'd be more than glad to be corrected too. -- Peter Xu
