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x86/alternatives: Use atomic_xchg() instead atomic_dec_and_test() for stop_machine_text_poke()

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stop_machine_text_poke() uses atomic_dec_and_test() to select one of
the CPUs executing that function to actually modify the code.

Since the variable is initialized to 1, subsequent CPUs will make the
variable go negative. Since going negative is uncommon/unexpected in
typical dec_and_test usage change this user to atomic_xchg().

This was found using a patch that warns on dec_and_test going
negative.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
[ Rewrote changelog ]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/87zk8fgsx9.fsf@devron.myhome.or.jp
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
OGAWA Hirofumi 2012-06-07 22:20:18 +09:00 committed by Ingo Molnar
parent b0a4c6f2e3
commit 2f74759056
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kernel/alternative.c
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@ -664,7 +664,7 @@ static int __kprobes stop_machine_text_poke(void *data)
struct text_poke_param *p;
int i;
if (atomic_dec_and_test(&stop_machine_first)) {
if (atomic_xchg(&stop_machine_first, 0)) {
for (i = 0; i < tpp->nparams; i++) {
p = &tpp->params[i];
text_poke(p->addr, p->opcode, p->len);