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From: "bugdal at aerifal dot cx" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sources.redhat.com
Subject: [Bug nptl/13184] rwlocks can go into dead lock
Date: Thu, 04 Oct 2012 17:56:00 -0000 [thread overview]
Message-ID: <bug-13184-131-MpdtjbeWGt@http.sourceware.org/bugzilla/> (raw)
In-Reply-To: <bug-13184-131@http.sourceware.org/bugzilla/>
http://sourceware.org/bugzilla/show_bug.cgi?id=13184
--- Comment #11 from Rich Felker <bugdal at aerifal dot cx> 2012-10-04 17:55:54 UTC ---
I agree that it's ridiculous to try to fix a hardware bug like this. The kernel
really should just refuse to do SMP on broken hardware like this unless it can
do a transparent workaround in kernelspace. Then AMD can deal with replacing
all the broken CPUs they sold when people start complaining that SMP no longer
works. Atomic ops being broken and needing workarounds is not part of the x86
or x86_64 ABI.
With that said, it would be nice to understand the bug. Is is that
lock-prefixed read-modify-write operations (like "lock;inc (%reg)") get
reordered with respect to xchg or lock-prefixed cmpxchg? Or is it only
non-lock-prefixed read-modify-write operations (like "inc (%reg)") that are
getting reordered with respect to the latter?
I don't think there's any workaround that would not incur significant costs on
non-broken systems, and even if there were, I think "fixing" this is wrong in
principle.
--- Comment #12 from Rich Felker <bugdal at aerifal dot cx> 2012-10-04 17:55:54 UTC ---
I agree that it's ridiculous to try to fix a hardware bug like this. The kernel
really should just refuse to do SMP on broken hardware like this unless it can
do a transparent workaround in kernelspace. Then AMD can deal with replacing
all the broken CPUs they sold when people start complaining that SMP no longer
works. Atomic ops being broken and needing workarounds is not part of the x86
or x86_64 ABI.
With that said, it would be nice to understand the bug. Is is that
lock-prefixed read-modify-write operations (like "lock;inc (%reg)") get
reordered with respect to xchg or lock-prefixed cmpxchg? Or is it only
non-lock-prefixed read-modify-write operations (like "inc (%reg)") that are
getting reordered with respect to the latter?
I don't think there's any workaround that would not incur significant costs on
non-broken systems, and even if there were, I think "fixing" this is wrong in
principle.
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next prev parent reply other threads:[~2012-10-04 17:56 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-12 21:19 [Bug nptl/13184] New: " redhat at pureftpd dot org
2011-09-12 21:33 ` [Bug nptl/13184] " bugdal at aerifal dot cx
2011-09-12 21:42 ` redhat at pureftpd dot org
2011-09-12 22:26 ` bugdal at aerifal dot cx
2011-09-12 22:41 ` redhat at pureftpd dot org
2011-09-13 1:57 ` redhat at pureftpd dot org
2011-09-13 2:02 ` redhat at pureftpd dot org
2012-01-16 20:03 ` ph.mathieu at gmail dot com
2012-01-16 21:47 ` redhat at pureftpd dot org
2012-01-17 14:54 ` ph.mathieu at gmail dot com
2012-10-04 12:31 ` siddhesh at redhat dot com
2012-10-04 12:37 ` bugdal at aerifal dot cx
2012-10-04 13:13 ` siddhesh at redhat dot com
2012-10-04 17:56 ` bugdal at aerifal dot cx [this message]
2012-10-04 17:56 ` bugdal at aerifal dot cx
2012-12-19 10:44 ` schwab@linux-m68k.org
2014-06-13 14:29 ` fweimer at redhat dot com
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