[apparmor] [PATCH] apparmor: try to avoid refing the label in apparmor_file_open

[Mateusz Guzik]

It can be done in the common case.

A 24-way open1_processes from will-it-scale (separate file open) shows:
  29.37%  [kernel]           [k] apparmor_file_open
  26.84%  [kernel]           [k] apparmor_file_alloc_security
  26.62%  [kernel]           [k] apparmor_file_free_security
   1.32%  [kernel]           [k] clear_bhb_loop

apparmor_file_open is eliminated from the profile with the patch.

Throughput (ops/s):
before: 6092196
after:  8309726 (+36%)

Signed-off-by: Mateusz Guzik <mjgu...@gmail.com>
---

I think this is a worthwhile touch up regardless of what happens with
label refcouting in the long run. It does not of course does not fully
fix the problem.

I concede the naming is not consistent with other stuff in the file and
I'm not going to argue about it -- happy to name it whatever as long as
the problem is sorted out.

Am I missing something which makes the approach below not work to begin
with?

 security/apparmor/include/cred.h | 20 ++++++++++++++++++++
 security/apparmor/lsm.c          |  5 +++--
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/security/apparmor/include/cred.h b/security/apparmor/include/cred.h
index 58fdc72af664..7265d2f81dd5 100644
--- a/security/apparmor/include/cred.h
+++ b/security/apparmor/include/cred.h
@@ -63,6 +63,26 @@ static inline struct aa_label 
*aa_get_newest_cred_label(const struct cred *cred)
        return aa_get_newest_label(aa_cred_raw_label(cred));
 }
 
+static inline struct aa_label *aa_get_newest_cred_label_condref(const struct 
cred *cred,
+                                                               bool *needput)
+{
+       struct aa_label *l = aa_cred_raw_label(cred);
+
+       if (unlikely(label_is_stale(l))) {
+               *needput = true;
+               return aa_get_newest_label(l);
+       }
+
+       *needput = false;
+       return l;
+}
+
+static inline void aa_put_label_condref(struct aa_label *l, bool needput)
+{
+       if (unlikely(needput))
+               aa_put_label(l);
+}
+
 /**
  * aa_current_raw_label - find the current tasks confining label
  *
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 2cea34657a47..4bf87eac4a56 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -461,6 +461,7 @@ static int apparmor_file_open(struct file *file)
        struct aa_file_ctx *fctx = file_ctx(file);
        struct aa_label *label;
        int error = 0;
+       bool needput;
 
        if (!path_mediated_fs(file->f_path.dentry))
                return 0;
@@ -477,7 +478,7 @@ static int apparmor_file_open(struct file *file)
                return 0;
        }
 
-       label = aa_get_newest_cred_label(file->f_cred);
+       label = aa_get_newest_cred_label_condref(file->f_cred, &needput);
        if (!unconfined(label)) {
                struct mnt_idmap *idmap = file_mnt_idmap(file);
                struct inode *inode = file_inode(file);
@@ -494,7 +495,7 @@ static int apparmor_file_open(struct file *file)
                /* todo cache full allowed permissions set and state */
                fctx->allow = aa_map_file_to_perms(file);
        }
-       aa_put_label(label);
+       aa_put_label_condref(label, needput);
 
        return error;
 }
-- 
2.43.0