[PATCH] arm_mpam: return allocation errors as error pointers

[Sang-Hoon Choi <csh0052@gmail.com>]

resctrl_arch_mon_ctx_alloc() stores the result of monitor allocation in
an allocated int. If monitor allocation fails, it still returns that pointer.
Callers check IS_ERR(), so they treat the failed allocation as a valid
monitor context and pass the error value on as a monitor index.

For example, if the wait for a free monitor ends because a signal is
pending, the stored result is still -ENOSPC. Other allocation errors
also reach the same return path.

Free the temporary allocation and return ERR_PTR(err) for negative
results. Leave successful indices and USE_PRE_ALLOCATED unchanged.

Fixes: 2a3c79c61539 ("arm_mpam: resctrl: Allow resctrl to allocate monitors")
Reported-by: Changyul Lee <lcy8047@gmail.com>
Link: https://github.com/lcy8047/radix-tree-bug-temp/blob/main/bug_list/idr-ida-xarray/wrong-id-value/IDR-BUG-33-mpam-monitor-id.md
Assisted-by: Sang-Hoon Choi <csh0052@gmail.com>
Signed-off-by: Sang-Hoon Choi <csh0052@gmail.com>
---
Compile-tested on arm64 with allmodconfig and W=1 against mainline
6f8319e3e9a44dd537d17f41565a8453c560a581. No hardware runtime test was
performed.

 drivers/resctrl/mpam_resctrl.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
index 9d223057953a..945be7465ad3 100644
--- a/drivers/resctrl/mpam_resctrl.c
+++ b/drivers/resctrl/mpam_resctrl.c
@@ -413,6 +413,13 @@ void *resctrl_arch_mon_ctx_alloc(struct rdt_resource *r,
 	} while (*ret == -ENOSPC && !signal_pending(current));
 	finish_wait(&resctrl_mon_ctx_waiters, &wait);
 
+	if (*ret < 0) {
+		int err = *ret;
+
+		kfree(ret);
+		return ERR_PTR(err);
+	}
+
 	return ret;
 }
 
-- 
2.43.0