linux-kernel - [PATCH 4.19 092/245] firmware: arm_sdei: Use cpus_read

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Date:   Tue, 29 Sep 2020 12:59:03 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, James Morse <james.morse@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 092/245] firmware: arm_sdei: Use cpus_read_lock() to avoid races with cpuhp

From: James Morse <james.morse@....com>

[ Upstream commit 54f529a6806c9710947a4f2cdc15d6ea54121ccd ]

SDEI has private events that need registering and enabling on each CPU.
CPUs can come and go while we are trying to do this. SDEI tries to avoid
these problems by setting the reregister flag before the register call,
so any CPUs that come online register the event too. Sticking plaster
like this doesn't work, as if the register call fails, a CPU that
subsequently comes online will register the event before reregister
is cleared.

Take cpus_read_lock() around the register and enable calls. We don't
want surprise CPUs to do the wrong thing if they race with these calls
failing.

Signed-off-by: James Morse <james.morse@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/firmware/arm_sdei.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/drivers/firmware/arm_sdei.c b/drivers/firmware/arm_sdei.c
index 05b528c7ed8fd..e809f4d9a9e93 100644
--- a/drivers/firmware/arm_sdei.c
+++ b/drivers/firmware/arm_sdei.c
@@ -410,14 +410,19 @@ int sdei_event_enable(u32 event_num)
 		return -ENOENT;
 	}
 
-	spin_lock(&sdei_list_lock);
-	event->reenable = true;
-	spin_unlock(&sdei_list_lock);
 
+	cpus_read_lock();
 	if (event->type == SDEI_EVENT_TYPE_SHARED)
 		err = sdei_api_event_enable(event->event_num);
 	else
 		err = sdei_do_cross_call(_local_event_enable, event);
+
+	if (!err) {
+		spin_lock(&sdei_list_lock);
+		event->reenable = true;
+		spin_unlock(&sdei_list_lock);
+	}
+	cpus_read_unlock();
 	mutex_unlock(&sdei_events_lock);
 
 	return err;
@@ -619,21 +624,18 @@ int sdei_event_register(u32 event_num, sdei_event_callback *cb, void *arg)
 			break;
 		}
 
-		spin_lock(&sdei_list_lock);
-		event->reregister = true;
-		spin_unlock(&sdei_list_lock);
-
+		cpus_read_lock();
 		err = _sdei_event_register(event);
 		if (err) {
-			spin_lock(&sdei_list_lock);
-			event->reregister = false;
-			event->reenable = false;
-			spin_unlock(&sdei_list_lock);
-
 			sdei_event_destroy(event);
 			pr_warn("Failed to register event %u: %d\n", event_num,
 				err);
+		} else {
+			spin_lock(&sdei_list_lock);
+			event->reregister = true;
+			spin_unlock(&sdei_list_lock);
 		}
+		cpus_read_unlock();
 	} while (0);
 	mutex_unlock(&sdei_events_lock);
 
-- 
2.25.1