linux-kernel - [PATCH v2] drop_caches: Allow re-enabling message after disabling

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20250317-jag-drop_caches_msg-v2-1-e22d9a6a3038@kernel.org>
Date: Mon, 17 Mar 2025 20:40:04 +0100
From: Joel Granados <joel.granados@...nel.org>
To: Jonathan Corbet <corbet@....net>, 
 Alexander Viro <viro@...iv.linux.org.uk>, 
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-fsdevel@...r.kernel.org, Ruiwu Chen <rwchen404@...il.com>, 
 Luis Chamberlain <mcgrof@...nel.org>, 
 Joel Granados <joel.granados@...nel.org>
Subject: [PATCH v2] drop_caches: Allow re-enabling message after disabling

After writing "4" to /proc/sys/vm/drop_caches there was no way to
re-enable the drop_caches kernel message. By replacing the "or"
assignment for the stfu variable, it is now possible to toggle the
message on and off by setting the 4th bit in /proc/sys/vm/drop_caches.

Signed-off-by: Joel Granados <joel.granados@...nel.org>
---
Changes in v2:
- Check the 4 bit before we actualy toggle the message
- Link to v1: https://lore.kernel.org/r/20250313-jag-drop_caches_msg-v1-1-c2e4e7874b72@kernel.org
---

---
 Documentation/admin-guide/sysctl/vm.rst | 2 +-
 fs/drop_caches.c                        | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index f48eaa98d22d2b575f6e913f437b0d548daac3e6..75a032f8cbfb4e05f04610cca219d154bd852789 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -266,7 +266,7 @@ used::
 	cat (1234): drop_caches: 3
 
 These are informational only.  They do not mean that anything is wrong
-with your system.  To disable them, echo 4 (bit 2) into drop_caches.
+with your system.  To toggle them, echo 4 (bit 2) into drop_caches.
 
 enable_soft_offline
 ===================
diff --git a/fs/drop_caches.c b/fs/drop_caches.c
index d45ef541d848a73cbd19205e0111c2cab3b73617..15730593ae39955ae7ae93aec17546fc96f89dce 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -68,12 +68,13 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 			drop_slab();
 			count_vm_event(DROP_SLAB);
 		}
+		if (sysctl_drop_caches & 4)
+			stfu ^= 1;
 		if (!stfu) {
 			pr_info("%s (%d): drop_caches: %d\n",
 				current->comm, task_pid_nr(current),
 				sysctl_drop_caches);
 		}
-		stfu |= sysctl_drop_caches & 4;
 	}
 	return 0;
 }

---
base-commit: 7eb172143d5508b4da468ed59ee857c6e5e01da6
change-id: 20250313-jag-drop_caches_msg-c4fbfedb51f3

Best regards,
-- 
Joel Granados <joel.granados@...nel.org>