NetBSD Problem Report #55230

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Date: Mon,  4 May 2020 15:04:47 +0000 (UTC)
From: thorpej@me.com
Reply-To: thorpej@me.com
To: gnats-bugs@NetBSD.org
Subject: futex wakes do not wake the highest priority waiter
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>Number:         55230
>Category:       kern
>Synopsis:       futex wakes do not wake the highest priority waiter
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon May 04 15:05:00 +0000 2020
>Last-Modified:  Mon May 04 15:10:01 +0000 2020
>Originator:     Jason Thorpe
>Release:        NetBSD 9.99.59
>Organization:
Riscy Business
>Environment:
NetBSD 9.99.59
>Description:
Futex wake operations do not wake the highest priority waiter.  Instead, the wake the waiters in FIFO order.
>How-To-Repeat:
Enqueue a low priority waiter before a high priority waiter.  Wake one waiter.  The waiter that's awoken will be the low priority waiter.
>Fix:
Do not use a queue of "wait" structures each with their own condvar.  Instead, each futex should have its own sleepq and operate as a first-class synchronization object.

>Audit-Trail:
From: "Jason R Thorpe" <thorpej@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/55230 CVS commit: src/tests/lib/libc/sys
Date: Mon, 4 May 2020 15:09:34 +0000

 Module Name:	src
 Committed By:	thorpej
 Date:		Mon May  4 15:09:34 UTC 2020

 Modified Files:
 	src/tests/lib/libc/sys: t_futex_ops.c

 Log Message:
 Add a test case for PR kern/55230.  It is currently marked as expect-fail.


 To generate a diff of this commit:
 cvs rdiff -u -r1.3 -r1.4 src/tests/lib/libc/sys/t_futex_ops.c

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

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