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Message-Id: <20221018001029.2731620-4-sashal@kernel.org>
Date: Mon, 17 Oct 2022 20:10:17 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: Marco Elver <elver@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
Ian Rogers <irogers@...gle.com>,
Sasha Levin <sashal@...nel.org>, mpe@...erman.id.au,
christophe.leroy@...roup.eu, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH AUTOSEL 5.10 04/16] powerpc/hw_breakpoint: Avoid relying on caller synchronization
From: Marco Elver <elver@...gle.com>
[ Upstream commit f95e5a3d59011eec1257d0e76de1e1f8969d426f ]
Internal data structures (cpu_bps, task_bps) of powerpc's hw_breakpoint
implementation have relied on nr_bp_mutex serializing access to them.
Before overhauling synchronization of kernel/events/hw_breakpoint.c,
introduce 2 spinlocks to synchronize cpu_bps and task_bps respectively,
thus avoiding reliance on callers synchronizing powerpc's hw_breakpoint.
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Marco Elver <elver@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Dmitry Vyukov <dvyukov@...gle.com>
Acked-by: Ian Rogers <irogers@...gle.com>
Link: https://lore.kernel.org/r/20220829124719.675715-10-elver@google.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
arch/powerpc/kernel/hw_breakpoint.c | 53 ++++++++++++++++++++++-------
1 file changed, 40 insertions(+), 13 deletions(-)
diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index f4e8f21046f5..b081e60ecc6a 100644
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -15,6 +15,7 @@
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/smp.h>
+#include <linux/spinlock.h>
#include <linux/debugfs.h>
#include <linux/init.h>
@@ -130,7 +131,14 @@ struct breakpoint {
bool ptrace_bp;
};
+/*
+ * While kernel/events/hw_breakpoint.c does its own synchronization, we cannot
+ * rely on it safely synchronizing internals here; however, we can rely on it
+ * not requesting more breakpoints than available.
+ */
+static DEFINE_SPINLOCK(cpu_bps_lock);
static DEFINE_PER_CPU(struct breakpoint *, cpu_bps[HBP_NUM_MAX]);
+static DEFINE_SPINLOCK(task_bps_lock);
static LIST_HEAD(task_bps);
static struct breakpoint *alloc_breakpoint(struct perf_event *bp)
@@ -175,7 +183,9 @@ static int task_bps_add(struct perf_event *bp)
if (IS_ERR(tmp))
return PTR_ERR(tmp);
+ spin_lock(&task_bps_lock);
list_add(&tmp->list, &task_bps);
+ spin_unlock(&task_bps_lock);
return 0;
}
@@ -183,6 +193,7 @@ static void task_bps_remove(struct perf_event *bp)
{
struct list_head *pos, *q;
+ spin_lock(&task_bps_lock);
list_for_each_safe(pos, q, &task_bps) {
struct breakpoint *tmp = list_entry(pos, struct breakpoint, list);
@@ -192,6 +203,7 @@ static void task_bps_remove(struct perf_event *bp)
break;
}
}
+ spin_unlock(&task_bps_lock);
}
/*
@@ -201,12 +213,17 @@ static void task_bps_remove(struct perf_event *bp)
static bool all_task_bps_check(struct perf_event *bp)
{
struct breakpoint *tmp;
+ bool ret = false;
+ spin_lock(&task_bps_lock);
list_for_each_entry(tmp, &task_bps, list) {
- if (!can_co_exist(tmp, bp))
- return true;
+ if (!can_co_exist(tmp, bp)) {
+ ret = true;
+ break;
+ }
}
- return false;
+ spin_unlock(&task_bps_lock);
+ return ret;
}
/*
@@ -216,13 +233,18 @@ static bool all_task_bps_check(struct perf_event *bp)
static bool same_task_bps_check(struct perf_event *bp)
{
struct breakpoint *tmp;
+ bool ret = false;
+ spin_lock(&task_bps_lock);
list_for_each_entry(tmp, &task_bps, list) {
if (tmp->bp->hw.target == bp->hw.target &&
- !can_co_exist(tmp, bp))
- return true;
+ !can_co_exist(tmp, bp)) {
+ ret = true;
+ break;
+ }
}
- return false;
+ spin_unlock(&task_bps_lock);
+ return ret;
}
static int cpu_bps_add(struct perf_event *bp)
@@ -235,6 +257,7 @@ static int cpu_bps_add(struct perf_event *bp)
if (IS_ERR(tmp))
return PTR_ERR(tmp);
+ spin_lock(&cpu_bps_lock);
cpu_bp = per_cpu_ptr(cpu_bps, bp->cpu);
for (i = 0; i < nr_wp_slots(); i++) {
if (!cpu_bp[i]) {
@@ -242,6 +265,7 @@ static int cpu_bps_add(struct perf_event *bp)
break;
}
}
+ spin_unlock(&cpu_bps_lock);
return 0;
}
@@ -250,6 +274,7 @@ static void cpu_bps_remove(struct perf_event *bp)
struct breakpoint **cpu_bp;
int i = 0;
+ spin_lock(&cpu_bps_lock);
cpu_bp = per_cpu_ptr(cpu_bps, bp->cpu);
for (i = 0; i < nr_wp_slots(); i++) {
if (!cpu_bp[i])
@@ -261,19 +286,25 @@ static void cpu_bps_remove(struct perf_event *bp)
break;
}
}
+ spin_unlock(&cpu_bps_lock);
}
static bool cpu_bps_check(int cpu, struct perf_event *bp)
{
struct breakpoint **cpu_bp;
+ bool ret = false;
int i;
+ spin_lock(&cpu_bps_lock);
cpu_bp = per_cpu_ptr(cpu_bps, cpu);
for (i = 0; i < nr_wp_slots(); i++) {
- if (cpu_bp[i] && !can_co_exist(cpu_bp[i], bp))
- return true;
+ if (cpu_bp[i] && !can_co_exist(cpu_bp[i], bp)) {
+ ret = true;
+ break;
+ }
}
- return false;
+ spin_unlock(&cpu_bps_lock);
+ return ret;
}
static bool all_cpu_bps_check(struct perf_event *bp)
@@ -287,10 +318,6 @@ static bool all_cpu_bps_check(struct perf_event *bp)
return false;
}
-/*
- * We don't use any locks to serialize accesses to cpu_bps or task_bps
- * because are already inside nr_bp_mutex.
- */
int arch_reserve_bp_slot(struct perf_event *bp)
{
int ret;
--
2.35.1
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