[PATCH v8 09/26] ACPI / APEI: Generalise the estatus queue's notify code

[James Morse <james.morse@arm.com>]

Refactor the estatus queue's pool notification routine from
NOTIFY_NMI's handlers. This will allow another notification
method to use the estatus queue without duplicating this code.

Add rcu_read_lock()/rcu_read_unlock() around the list
list_for_each_entry_rcu() walker. These aren't strictly necessary as
the whole nmi_enter/nmi_exit() window is a spooky RCU read-side
critical section.

in_nmi_queue_one_entry() is separate from the rcu-list walker for a
later caller that doesn't need to walk a list.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Punit Agrawal <punit.agrawal@arm.com>
Tested-by: Tyler Baicar <tbaicar@codeaurora.org>

---
Changes since v7:
 * Moved err= onto a separate line to make this more readable
 * Dropped ghes_ prefix on new static functions
 * Renamed stuff, 'notify' has an overloaded meaning,

Changes since v6:
 * Removed pool grow/remove code as this is no longer necessary.

Changes since v3:
 * Removed duplicate or redundant paragraphs in commit message.
 * Fixed the style of a zero check.
Changes since v1:
   * Tidied up _in_nmi_notify_one().
---
 drivers/acpi/apei/ghes.c | 65 ++++++++++++++++++++++++++--------------
 1 file changed, 43 insertions(+), 22 deletions(-)

diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
index af3c10f47f20..cb3d88de711f 100644
--- a/drivers/acpi/apei/ghes.c
+++ b/drivers/acpi/apei/ghes.c
@@ -912,37 +912,58 @@ static void __process_error(struct ghes *ghes)
 #endif
 }
 
-static int ghes_notify_nmi(unsigned int cmd, struct pt_regs *regs)
+static int ghes_in_nmi_queue_one_entry(struct ghes *ghes)
 {
 	u64 buf_paddr;
-	struct ghes *ghes;
-	int sev, ret = NMI_DONE;
+	int sev;
 
-	if (!atomic_add_unless(&ghes_in_nmi, 1, 1))
-		return ret;
+	if (ghes_read_estatus(ghes, &buf_paddr)) {
+		ghes_clear_estatus(ghes, buf_paddr);
+		return -ENOENT;
+	}
 
-	list_for_each_entry_rcu(ghes, &ghes_nmi, list) {
-		if (ghes_read_estatus(ghes, &buf_paddr)) {
-			ghes_clear_estatus(ghes, buf_paddr);
-			continue;
-		} else {
-			ret = NMI_HANDLED;
-		}
+	sev = ghes_severity(ghes->estatus->error_severity);
+	if (sev >= GHES_SEV_PANIC) {
+		ghes_print_queued_estatus();
+		__ghes_panic(ghes, buf_paddr);
+	}
 
-		sev = ghes_severity(ghes->estatus->error_severity);
-		if (sev >= GHES_SEV_PANIC) {
-			ghes_print_queued_estatus();
-			__ghes_panic(ghes, buf_paddr);
-		}
+	__process_error(ghes);
+	ghes_clear_estatus(ghes, buf_paddr);
 
-		__process_error(ghes);
-		ghes_clear_estatus(ghes, buf_paddr);
+	return 0;
+}
+
+static int ghes_in_nmi_spool_from_list(struct list_head *rcu_list)
+{
+	int err, ret = -ENOENT;
+	struct ghes *ghes;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(ghes, rcu_list, list) {
+		err = ghes_in_nmi_queue_one_entry(ghes);
+		if (!err)
+			ret = 0;
 	}
+	rcu_read_unlock();
 
-#ifdef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
-	if (ret == NMI_HANDLED)
+	if (IS_ENABLED(CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG) && !ret)
 		irq_work_queue(&ghes_proc_irq_work);
-#endif
+
+	return ret;
+}
+
+static int ghes_notify_nmi(unsigned int cmd, struct pt_regs *regs)
+{
+	int err, ret = NMI_DONE;
+
+	if (!atomic_add_unless(&ghes_in_nmi, 1, 1))
+		return ret;
+
+	err = ghes_in_nmi_spool_from_list(&ghes_nmi);
+	if (!err)
+		ret = NMI_HANDLED;
+
 	atomic_dec(&ghes_in_nmi);
 	return ret;
 }
-- 
2.20.1


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