linux-kernel - [tip: x86/urgent] x86/resctrl: Fix potential lockdep warning

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Date:   Wed, 13 Nov 2019 11:47:06 -0000
From:   "tip-bot2 for Xiaochen Shen" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Xiaochen Shen <xiaochen.shen@...el.com>,
        Borislav Petkov <bp@...e.de>, Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        pei.p.jia@...el.com, Thomas Gleixner <tglx@...utronix.de>,
        "x86-ml" <x86@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/resctrl: Fix potential lockdep warning

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     c8eafe1495303bfd0eedaa8156b1ee9082ee9642
Gitweb:        https://git.kernel.org/tip/c8eafe1495303bfd0eedaa8156b1ee9082ee9642
Author:        Xiaochen Shen <xiaochen.shen@...el.com>
AuthorDate:    Thu, 07 Nov 2019 06:36:36 +08:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Wed, 13 Nov 2019 12:34:44 +01:00

x86/resctrl: Fix potential lockdep warning

rdtgroup_cpus_write() and mkdir_rdt_prepare() call
rdtgroup_kn_lock_live() -> kernfs_to_rdtgroup() to get 'rdtgrp', and
then call the rdt_last_cmd_{clear,puts,...}() functions which will check
if rdtgroup_mutex is held/requires its caller to hold rdtgroup_mutex.

But if 'rdtgrp' returned from kernfs_to_rdtgroup() is NULL,
rdtgroup_mutex is not held and calling rdt_last_cmd_{clear,puts,...}()
will result in a self-incurred, potential lockdep warning.

Remove the rdt_last_cmd_{clear,puts,...}() calls in these two paths.
Just returning error should be sufficient to report to the user that the
entry doesn't exist any more.

 [ bp: Massage. ]

Fixes: 94457b36e8a5 ("x86/intel_rdt: Add diagnostics when writing the cpus file")
Fixes: cfd0f34e4cd5 ("x86/intel_rdt: Add diagnostics when making directories")
Signed-off-by: Xiaochen Shen <xiaochen.shen@...el.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Reviewed-by: Fenghua Yu <fenghua.yu@...el.com>
Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: pei.p.jia@...el.com
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: x86-ml <x86@...nel.org>
Link: https://lkml.kernel.org/r/1573079796-11713-1-git-send-email-xiaochen.shen@intel.com
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index a46dee8..2e3b06d 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -461,10 +461,8 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
 	}
 
 	rdtgrp = rdtgroup_kn_lock_live(of->kn);
-	rdt_last_cmd_clear();
 	if (!rdtgrp) {
 		ret = -ENOENT;
-		rdt_last_cmd_puts("Directory was removed\n");
 		goto unlock;
 	}
 
@@ -2648,10 +2646,8 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
 	int ret;
 
 	prdtgrp = rdtgroup_kn_lock_live(prgrp_kn);
-	rdt_last_cmd_clear();
 	if (!prdtgrp) {
 		ret = -ENODEV;
-		rdt_last_cmd_puts("Directory was removed\n");
 		goto out_unlock;
 	}