Re: [PATCH] Re: today's futex changes

Rusty Russell
2003-09-09T02:30:20Z

In message <Pine.LNX.4.44.0309081746180.7008-100000@localhost.localdomain> you write:
> Most of it (the futex_wait tweaks) looked fine to me -
> though I look forward to the first report of that BUG().

Me too. But at least we'll *get* a report if someone does spurious
wakeups.

> Part 2, requiring VM_WRITE and removing the comment on VM_MAYSHARE,
> seems a regression to me. Perhaps I misinterpreted Linus' action in
> taking Jamie's patch: I took that to mean he relented a little on his
> hardline position about VM_SHARED, and now accepts that in this context
> VM_MAYSHARE is more appropriate (easier to document). I know I argued
> that readonly futices are pointless, but I thought Jamie gave a good
> picture of how a readonly view could still be used. I'd rather that
> part were a separate patch, so Linus can merge or not as he wishes.

Sure, I jumboed them together for feedback from you guys.

All users I am currently aware of won't care either way. Current
test-5 is:

Sees Changes Sees FUTEX_WAKE
from another MAP_SHARED from another MAP_SHARED

MAP_PRIVATE read-only: Y N
MAP_PRIVATE read-write: Y* N
MAP_SHARED read-only: Y Y
MAP_SHARED read-write: Y Y

[* Only until page is written to, after which COW splits them ]

Previously, the FUTEX_WAKE column was identical to the first column.
Now, IMHO, this new semantic is more sensible, but I don't really
mind.

But I don't recall anything about believable use of RO futexes: Jamie?

Cheers,
Rusty.
--
Anyone who quotes me in their sig is an idiot. -- Rusty Russell.