[tip: x86/entry] x86/int3: Avoid atomic instrumentation

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the x86/entry branch of tip:

Commit-ID:     a53a1d0435cdc2b66f41f75fa1cee31e8fe6d99e
Gitweb:        https://git.kernel.org/tip/a53a1d0435cdc2b66f41f75fa1cee31e8fe6d99e
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Fri, 24 Jan 2020 22:08:45 +01:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Tue, 19 May 2020 16:04:05 +02:00

x86/int3: Avoid atomic instrumentation

Use arch_atomic_*() and __READ_ONCE() to ensure nothing untoward
creeps in and ruins things.

That is; this is the INT3 text poke handler, strictly limit the code
that runs in it, lest it inadvertenly hits yet another INT3.

Reported-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Reviewed-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
Acked-by: Andy Lutomirski <luto@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200505135313.517429268@xxxxxxxxxxxxx


---
 arch/x86/kernel/alternative.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 1f4cb2c..686c8ac 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -960,9 +960,9 @@ static struct bp_patching_desc *bp_desc;
 static __always_inline
 struct bp_patching_desc *try_get_desc(struct bp_patching_desc **descp)
 {
-	struct bp_patching_desc *desc = READ_ONCE(*descp); /* rcu_dereference */
+	struct bp_patching_desc *desc = __READ_ONCE(*descp); /* rcu_dereference */
 
-	if (!desc || !atomic_inc_not_zero(&desc->refs))
+	if (!desc || !arch_atomic_inc_not_zero(&desc->refs))
 		return NULL;
 
 	return desc;
@@ -971,7 +971,7 @@ struct bp_patching_desc *try_get_desc(struct bp_patching_desc **descp)
 static __always_inline void put_desc(struct bp_patching_desc *desc)
 {
 	smp_mb__before_atomic();
-	atomic_dec(&desc->refs);
+	arch_atomic_dec(&desc->refs);
 }
 
 static __always_inline void *text_poke_addr(struct text_poke_loc *tp)