diff mbox series

[RFC,4/4] mitigations: Add flock cache accounting to 'mitigations=off'

Message ID 3e803d5aee5dd1f4c738f0de1e839e6cfcb9dc41.1705507931.git.jpoimboe@kernel.org
State New
Headers
Series Fix file lock cache accounting, again |

Commit Message

Josh Poimboeuf Jan. 17, 2024, 4:14 p.m. UTC 
  Allow flock cache accounting to be disabled with 'mitigations=off', as
it fits the profile for that option: trusted user space combined with a
performance-impacting mitigation.

Also, for consistency with the other CONFIG_MITIGATION_* options, rename
CONFIG_FLOCK_ACCOUNTING to CONFIG_MITIGATION_FLOCK_ACCOUNTING.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt | 4 ++++
 fs/Kconfig                                      | 2 +-
 fs/locks.c                                      | 5 +++--
 3 files changed, 8 insertions(+), 3 deletions(-)

Comments

Michal Koutný Jan. 18, 2024, 9:04 a.m. UTC | #1 
On Wed, Jan 17, 2024 at 08:14:46AM -0800, Josh Poimboeuf <jpoimboe@kernel.org> wrote:
> Allow flock cache accounting to be disabled with 'mitigations=off', as
> it fits the profile for that option: trusted user space combined with a
> performance-impacting mitigation.

Note that some other kernel objects that don't have any other tight
limit are already charged too (but their charging likely did not stand
out in any performance regression tests).
In the situation you describe, users can already pass
`cgroup.memory=nokmem` and get rid of charging overhead in general.

IOW, if flock objects are charged, there already is a boot option to
turn off such behavior.

Regards,
Michal
diff mbox series

Patch

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 24e873351368..b31fe7433b48 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3427,6 +3427,10 @@ 
 					       ssbd=force-off [ARM64]
 					       tsx_async_abort=off [X86]
 
+					       Software mitigations:
+					       ---------------------
+					       flock_accounting=off [KNL]
+
 				Exceptions:
 					       This does not have any effect on
 					       kvm.nx_huge_pages when
diff --git a/fs/Kconfig b/fs/Kconfig
index 591f54a03059..4345b79d3b40 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -129,7 +129,7 @@  config FILE_LOCKING
           for filesystems like NFS and for the flock() system
           call. Disabling this option saves about 11k.
 
-config FLOCK_ACCOUNTING
+config MITIGATION_FLOCK_ACCOUNTING
 	bool "Enable kernel memory accounting for file locks" if EXPERT
 	depends on FILE_LOCKING
 	default y
diff --git a/fs/locks.c b/fs/locks.c
index e2799a18c4e8..fd4157ccd504 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -64,6 +64,7 @@ 
 #include <linux/hashtable.h>
 #include <linux/percpu.h>
 #include <linux/sysctl.h>
+#include <linux/mitigations.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/filelock.h>
@@ -2905,7 +2906,7 @@  static int __init proc_locks_init(void)
 fs_initcall(proc_locks_init);
 #endif
 
-static bool flock_accounting __ro_after_init = IS_ENABLED(CONFIG_FLOCK_ACCOUNTING);
+static bool flock_accounting __ro_after_init = IS_ENABLED(CONFIG_MITIGATION_FLOCK_ACCOUNTING);
 
 static int __init flock_accounting_cmdline(char *str)
 {
@@ -2930,7 +2931,7 @@  static int __init filelock_init(void)
 	int i;
 	slab_flags_t flags = SLAB_PANIC;
 
-	if (!flock_accounting)
+	if (mitigations_off() || !flock_accounting)
 		pr_err(FLOCK_ACCOUNTING_MSG);
 	else
 		flags |= SLAB_ACCOUNT;