linux-kernel - [PATCH v2] fs/resctrl: Restore the rdt_last_cmd_clear() calls after acquiring rdtgroup

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Message-ID: <20250603125828.1590067-1-zengheng4@huawei.com>
Date: Tue, 3 Jun 2025 20:58:28 +0800
From: Zeng Heng <zengheng4@...wei.com>
To: <tony.luck@...el.com>, <reinette.chatre@...el.com>, <Dave.Martin@....com>,
	<fenghuay@...dia.com>, <bp@...en8.de>, <james.morse@....com>
CC: <bobo.shaobowang@...wei.com>, <linux-kernel@...r.kernel.org>,
	<x86@...nel.org>
Subject: [PATCH v2] fs/resctrl: Restore the rdt_last_cmd_clear() calls after acquiring rdtgroup_mutex

A lockdep fix removed two rdt_last_cmd_clear() calls that were used
to clear the last_cmd_status buffer but called without holding the
required rdtgroup_mutex. The impacted resctrl commands are:
writing to the cpus or cpus_list files and creating a new monitor
or control group. With stale data in the last_cmd_status buffer the
impacted resctrl commands report the stale error on success, or append
its own failure message to the stale error on failure.

Consequently, restore the rdt_last_cmd_clear() calls after acquiring
rdtgroup_mutex.

Fixes: c8eafe149530 ("x86/resctrl: Fix potential lockdep warning")
Signed-off-by: Zeng Heng <zengheng4@...wei.com>
---
Changes in v2:
1. Move rdt_last_cmd_clear() to be right after acquiring the mutex.
2. Rewrite the commit message in imperative tone, add explanation of the
   error phenomenon.
Link to v1: https://lore.kernel.org/all/20250529113353.3275066-1-zengheng4@huawei.com/

 fs/resctrl/rdtgroup.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index cc37f58b47dd..1beb124e25f6 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -536,6 +536,8 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
 		goto unlock;
 	}

+	rdt_last_cmd_clear();
+
 	if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED ||
 	    rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
 		ret = -EINVAL;
@@ -3472,6 +3474,8 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
 		goto out_unlock;
 	}

+	rdt_last_cmd_clear();
+
 	/*
 	 * Check that the parent directory for a monitor group is a "mon_groups"
 	 * directory.
--
2.25.1