[PATCH 4/4] RAS/amd/fmpm: Fix spurious BUG when ERST record enumeration fails

["Rui Qi" <qirui.001@bytedance.com>]

When erst_get_record_id_begin() returns an error, get_saved_records()
jumps to the out_end label which unconditionally calls
erst_get_record_id_end(). This is wrong because:

- If erst_disable is true, begin() returns -ENODEV without
  incrementing the refcount. Then end() hits BUG_ON(erst_disable)
  and panics.

- If mutex_lock_interruptible() is interrupted, begin() returns
  -EINTR without incrementing the refcount. Then end() decrements
  refcount below zero, hitting BUG_ON(refcount < 0).

The comment in erst_get_record_id_end() explicitly states that it
should not be called when erst_get_record_id_begin() failed.

Fix by adding a separate out_free label that only does kfree(),
skipping the erst_get_record_id_end() call when begin() failed.

Fixes: 6f15e617cc99 ("RAS: Introduce a FRU memory poison manager")
Signed-off-by: Rui Qi <qirui.001@bytedance.com>
---
 drivers/ras/amd/fmpm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/ras/amd/fmpm.c b/drivers/ras/amd/fmpm.c
index 14a103de9d62..22627f6278c0 100644
--- a/drivers/ras/amd/fmpm.c
+++ b/drivers/ras/amd/fmpm.c
@@ -675,7 +675,7 @@ static int get_saved_records(void)
 
 	ret = erst_get_record_id_begin(&pos);
 	if (ret < 0)
-		goto out_end;
+		goto out_free;
 
 	while (!erst_get_record_id_next(&pos, &record_id)) {
 		if (record_id == APEI_ERST_INVALID_RECORD_ID)
@@ -716,6 +716,7 @@ static int get_saved_records(void)
 
 out_end:
 	erst_get_record_id_end();
+out_free:
 	kfree(old);
 out:
 	return ret;
-- 
2.20.1