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Subject[tip:perfcounters/urgent] x86: atomic64: Fix unclean type use in atomic64_xchg()
Commit-ID:  199e23780a7e75c63a9e3d1108804e3af450ea3e
Gitweb: http://git.kernel.org/tip/199e23780a7e75c63a9e3d1108804e3af450ea3e
Author: Ingo Molnar <mingo@elte.hu>
AuthorDate: Fri, 3 Jul 2009 13:02:39 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 3 Jul 2009 13:26:46 +0200

x86: atomic64: Fix unclean type use in atomic64_xchg()

Linus noticed that atomic64_xchg() uses atomic_read(), which
happens to work because atomic_read() is a macro so the
.counter value gets u64-read on 32-bit too - but this is really
bogus and serious bugs are waiting to happen.

Fix atomic64_xchg() to use __atomic64_read() instead.

No code changed:

arch/x86/lib/atomic64_32.o:

text data bss dec hex filename
435 0 0 435 1b3 atomic64_32.o.before
435 0 0 435 1b3 atomic64_32.o.after

md5:
bd8ab95e69c93518578bfaf0ea3be4d9 atomic64_32.o.before.asm
bd8ab95e69c93518578bfaf0ea3be4d9 atomic64_32.o.after.asm

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
LKML-Reference: <alpine.LFD.2.01.0907021653030.3210@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
arch/x86/lib/atomic64_32.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/arch/x86/lib/atomic64_32.c b/arch/x86/lib/atomic64_32.c
index a910238..fd28fd3 100644
--- a/arch/x86/lib/atomic64_32.c
+++ b/arch/x86/lib/atomic64_32.c
@@ -36,7 +36,7 @@ u64 atomic64_xchg(atomic64_t *ptr, u64 new_val)
u64 old_val;

do {
- old_val = atomic_read(ptr);
+ old_val = __atomic64_read(ptr);
} while (atomic64_cmpxchg(ptr, old_val, new_val) != old_val);

return old_val;

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