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

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Message-Id: <20250313-jag-drop_caches_msg-v1-1-c2e4e7874b72@kernel.org>
Date: Thu, 13 Mar 2025 16:46:36 +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] 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 removing the "or" logic for
the stfu variable in drop_cache_sysctl_handler, 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>
---
 Documentation/admin-guide/sysctl/vm.rst | 2 +-
 fs/drop_caches.c                        | 2 +-
 2 files changed, 2 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..501b9f690445e245f88cbb31a5123b2752e2e7ce 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -73,7 +73,7 @@ int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 				current->comm, task_pid_nr(current),
 				sysctl_drop_caches);
 		}
-		stfu |= sysctl_drop_caches & 4;
+		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>