linux-kernel - [PATCH RFC 2/4] fs/locks: Add CONFIG_FLOCK

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Date: Wed, 17 Jan 2024 08:14:44 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
	Jeff Layton <jlayton@...nel.org>,
	Chuck Lever <chuck.lever@...cle.com>,
	Shakeel Butt <shakeelb@...gle.com>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>
Cc: linux-kernel@...r.kernel.org,
	Jens Axboe <axboe@...nel.dk>,
	Tejun Heo <tj@...nel.org>,
	Vasily Averin <vasily.averin@...ux.dev>,
	Michal Koutny <mkoutny@...e.com>,
	Waiman Long <longman@...hat.com>,
	Muchun Song <muchun.song@...ux.dev>,
	Jiri Kosina <jikos@...nel.org>,
	cgroups@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH RFC 2/4] fs/locks: Add CONFIG_FLOCK_ACCOUNTING

Allow flock cache accounting to be disabled at build time.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.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