On 8/29/25 1:39 PM, Sebastian Andrzej Siewior wrote:

On 2025-08-29 12:43:26 [-0400], Carlos O'Donell wrote:

quoted

quoted

index 69df4036ada7f..027e91b826bf1 100644

--- a/man/man2/futex.2
+++ b/man/man2/futex.2

@@ -6,10 +6,10 @@
   .\"
   .\" FIXME Still to integrate are some points from Torvald Riegel's mail of
   .\" 2015-01-23:
-.\"       http://thread.gmane.org/gmane.linux.kernel/1703405/focus=7977
+.\"       https://lore.kernel.org/lkml/1422037788.29655.0.camel@triegel.csb

Wrong link?

Should be this link:
https://lore.kernel.org/lkml/1422037145.27573.0.camel@triegel.csb/ (local)

Where the discussion is about the unresolved constraint to guarantee FIFO order.

I thought it is the longer email, the second that day, where he made
three points. Didn't read it (yet)…

Given the dates and the disjoint set of topics, my suggestion is the link above.

Now FIFO ordering you say. Is it glibc's side or kernel side? The kernel
sorts the futex waiters according their (task's) priority. It is not
FIFO unless the tasks are of equal priority.

The FIFO order question was a kernel-side question wrt futex semantics.
At least that's how I read the thread. And the issue was resolved, but possibly
not documented. Documentation might include stating "FIFO ordering over all
waiters, or even a subset of waiters (at the same priority level) is not
guaranteed."

Torvald was right that for POSIX condition variables we would naturally want
a FIFO wake order so earlier sleepers are woken first.

So a futex requeue will take the task with the highest priority from
uaddr1 and move it to uaddr2.

Right.

-- 
Cheers,
Carlos.