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From: Josh Poimboeuf <jpoimboe@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>,
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Cc: linux-kernel@vger.kernel.org,
	Jens Axboe <axboe@kernel.dk>,
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	Jiri Kosina <jikos@kernel.org>,
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	linux-mm@kvack.org
Subject: [PATCH RFC 2/4] fs/locks: Add CONFIG_FLOCK_ACCOUNTING
Date: Wed, 17 Jan 2024 08:14:44 -0800
Message-ID: <e3e0323c6291c3ceab18f9e39bf772d98b29f81e.1705507931.git.jpoimboe@kernel.org>
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Allow flock cache accounting to be disabled at build time.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 fs/Kconfig | 15 +++++++++++++++
 fs/locks.c |  2 +-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/fs/Kconfig b/fs/Kconfig
index a3159831ba98..591f54a03059 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -129,6 +129,21 @@ config FILE_LOCKING
           for filesystems like NFS and for the flock() system
           call. Disabling this option saves about 11k.
 
+config FLOCK_ACCOUNTING
+	bool "Enable kernel memory accounting for file locks" if EXPERT
+	depends on FILE_LOCKING
+	default y
+	help
+	  This option enables kernel memory accounting for file locks.  This
+	  prevents task groups from exceeding their memcg allocation limits.
+	  However, it may cause slowdowns in the flock() system call.
+
+	  Disabling this option is not recommended as it may allow a rogue task
+	  to DoS the system by forcing the kernel to allocate memory beyond the
+	  task group's memcg limits.
+
+	  If unsure, say Y.
+
 source "fs/crypto/Kconfig"
 
 source "fs/verity/Kconfig"
diff --git a/fs/locks.c b/fs/locks.c
index 235ac56c557d..e2799a18c4e8 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -2905,7 +2905,7 @@ static int __init proc_locks_init(void)
 fs_initcall(proc_locks_init);
 #endif
 
-static bool flock_accounting __ro_after_init = true;
+static bool flock_accounting __ro_after_init = IS_ENABLED(CONFIG_FLOCK_ACCOUNTING);
 
 static int __init flock_accounting_cmdline(char *str)
 {
-- 
2.43.0