NetBSD Problem Report #48999

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Date: Tue, 15 Jul 2014 22:59:25 +0000 (UTC)
From: jmcneill@invisible.ca
Reply-To: jmcneill@invisible.ca
To: gnats-bugs@NetBSD.org
Subject: [drm] Incorrect return value from test_and_set_bit
X-Send-Pr-Version: www-1.0

>Number:         48999
>Category:       kern
>Synopsis:       [drm] Incorrect return value from test_and_set_bit
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    riastradh
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jul 15 23:00:00 +0000 2014
>Closed-Date:    Sat Oct 04 15:52:08 +0000 2014
>Last-Modified:  Sat Oct 04 15:55:00 +0000 2014
>Originator:     Jared McNeill
>Release:        HEAD
>Organization:
>Environment:
>Description:
Docs for test_and_set_bit [1] say:

> WARNING! It is incredibly important that the value be a boolean,
> ie. "0" or "1".  Do not try to be fancy and save a few instructions by
> declaring the above to return "long" and just returning something like
> "old_val & mask" because that will not work.

But the implementation of this function in drm and drm2 both do "old_val & mask":

http://nxr.netbsd.org/xref/src/sys/external/bsd/drm/dist/bsd-core/drm_atomic.h#104

http://nxr.netbsd.org/xref/src/sys/external/bsd/drm2/include/linux/atomic.h#180
http://nxr.netbsd.org/xref/src/sys/external/bsd/drm2/include/linux/atomic.h#193
http://nxr.netbsd.org/xref/src/sys/external/bsd/drm2/include/linux/atomic.h#206

[1] https://www.kernel.org/doc/Documentation/atomic_ops.txt
>How-To-Repeat:

>Fix:

>Release-Note:

>Audit-Trail:

Responsible-Changed-From-To: kern-bug-people->riastradh
Responsible-Changed-By: dholland@NetBSD.org
Responsible-Changed-When: Wed, 16 Jul 2014 01:23:28 +0000
Responsible-Changed-Why:
by request


State-Changed-From-To: open->closed
State-Changed-By: riastradh@NetBSD.org
State-Changed-When: Thu, 17 Jul 2014 14:32:31 +0000
State-Changed-Why:
fixed in rev. 1.7 of linux/atomic.h


From: "Taylor R Campbell" <riastradh@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/48999 CVS commit: src/sys/external/bsd/drm2/include/linux
Date: Thu, 17 Jul 2014 14:30:33 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Thu Jul 17 14:30:33 UTC 2014

 Modified Files:
 	src/sys/external/bsd/drm2/include/linux: atomic.h bitops.h

 Log Message:
 Correct return values of Linux test-and-set operations (PR 48999).

 Linux's Documentation/atomic_ops.txt says in no uncertain terms these
 must return 0 or 1, not zero or nonzero.  I don't think this has
 caused an issue for drm (yet), but better to have it right.


 To generate a diff of this commit:
 cvs rdiff -u -r1.6 -r1.7 src/sys/external/bsd/drm2/include/linux/atomic.h
 cvs rdiff -u -r1.5 -r1.6 src/sys/external/bsd/drm2/include/linux/bitops.h

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

State-Changed-From-To: closed->open
State-Changed-By: mrg@NetBSD.org
State-Changed-When: Fri, 18 Jul 2014 01:53:35 +0000
State-Changed-Why:
not fixed in drm yet.


State-Changed-From-To: open->closed
State-Changed-By: riastradh@NetBSD.org
State-Changed-When: Sat, 04 Oct 2014 15:52:08 +0000
State-Changed-Why:
fixed in rev. 1.5 of drm_atomic.h


From: "Taylor R Campbell" <riastradh@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/48999 CVS commit: src/sys/external/bsd/drm/dist/bsd-core
Date: Sat, 4 Oct 2014 15:51:23 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Sat Oct  4 15:51:23 UTC 2014

 Modified Files:
 	src/sys/external/bsd/drm/dist/bsd-core: drm_atomic.h

 Log Message:
 Canonicalize boolean result from test_and_set_bit.

 Not actually semantically significant for any callers, but Linux
 documentation insists it is important, so we'll follow suit.

 Fixes last part of PR kern/48999.


 To generate a diff of this commit:
 cvs rdiff -u -r1.4 -r1.5 src/sys/external/bsd/drm/dist/bsd-core/drm_atomic.h

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

>Unformatted:

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