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    SubjectRe: [RFCv2] security: smack: add a hash table to quicken smk_find_entry()
    On 6/27/2013 2:11 PM, Casey Schaufler wrote:
    > On 6/11/2013 5:55 AM, Tomasz Stanislawski wrote:
    >> This patch adds a hash table to quicken searching of a smack label by its name.
    >>
    >> Basically, the patch improves performance of SMACK initialization. Parsing of
    >> rules involves translation from a string to a smack_known (aka label) entity
    >> which is done in smk_find_entry().
    >>
    >> The current implementation of the function iterates over a global list of
    >> smack_known resulting in O(N) complexity for smk_find_entry(). The total
    >> complexity of SMACK initialization becomes O(rules * labels). Therefore it
    >> scales quadratically with a complexity of a system.
    >>
    >> Applying the patch reduced the complexity of smk_find_entry() to O(1) as long
    >> as number of label is in hundreds. If the number of labels is increased please
    >> update SMACK_HASH_SLOTS constant defined in security/smack/smack.h. Introducing
    >> the configuration of this constant with Kconfig or cmdline might be a good
    >> idea.
    >>
    >> The size of the hash table was adjusted experimentally. The rule set used by
    >> TIZEN contains circa 17K rules for 500 labels. The table above contains
    >> results of SMACK initialization using 'time smackctl apply' bash command.
    >> The 'Ref' is a kernel without this patch applied. The consecutive values
    >> refers to value of SMACK_HASH_SLOTS. Every measurement was repeated three
    >> times to reduce noise.
    >>
    >> | Ref | 1 | 2 | 4 | 8 | 16 | 32 | 64 | 128 | 256 | 512
    >> --------------------------------------------------------------------------------------------
    >> Run1 | 1.156 | 1.096 | 0.883 | 0.764 | 0.692 | 0.667 | 0.649 | 0.633 | 0.634 | 0.629 | 0.620
    >> Run2 | 1.156 | 1.111 | 0.885 | 0.764 | 0.694 | 0.661 | 0.649 | 0.651 | 0.634 | 0.638 | 0.623
    >> Run3 | 1.160 | 1.107 | 0.886 | 0.764 | 0.694 | 0.671 | 0.661 | 0.638 | 0.631 | 0.624 | 0.638
    >> AVG | 1.157 | 1.105 | 0.885 | 0.764 | 0.693 | 0.666 | 0.653 | 0.641 | 0.633 | 0.630 | 0.627
    >>
    >> Surprisingly, a single hlist is slightly faster than a double-linked list.
    >> The speed-up saturates near 64 slots. Therefore I chose value 128 to provide
    >> some margin if more labels were used.
    >> It looks that IO becomes a new bottleneck.
    >>
    >> Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com>
    > I will take this into my tree after changing SMACK_HASH_SLOTS to 16.
    >
    > Acked-by: Casey Schaufler <casey@schaufler-ca.com>

    Applied to git://git.gitorious.org/smack-next/kernel.git#smack-for-3.12

    Rebasing was required. The change has been tested.


    >
    >> ---
    >> security/smack/smack.h | 5 +++++
    >> security/smack/smack_access.c | 30 +++++++++++++++++++++++++++---
    >> security/smack/smack_lsm.c | 12 ++++++------
    >> 3 files changed, 38 insertions(+), 9 deletions(-)
    >>
    >> diff --git a/security/smack/smack.h b/security/smack/smack.h
    >> index 339614c..b1d9441 100644
    >> --- a/security/smack/smack.h
    >> +++ b/security/smack/smack.h
    >> @@ -53,6 +53,7 @@
    >> */
    >> struct smack_known {
    >> struct list_head list;
    >> + struct hlist_node smk_hashed;
    >> char *smk_known;
    >> u32 smk_secid;
    >> struct netlbl_lsm_secattr smk_netlabel; /* on wire labels */
    >> @@ -222,6 +223,7 @@ char *smk_parse_smack(const char *string, int len);
    >> int smk_netlbl_mls(int, char *, struct netlbl_lsm_secattr *, int);
    >> char *smk_import(const char *, int);
    >> struct smack_known *smk_import_entry(const char *, int);
    >> +void smk_insert_entry(struct smack_known *skp);
    >> struct smack_known *smk_find_entry(const char *);
    >> u32 smack_to_secid(const char *);
    >>
    >> @@ -247,6 +249,9 @@ extern struct list_head smk_netlbladdr_list;
    >>
    >> extern struct security_operations smack_ops;
    >>
    >> +#define SMACK_HASH_SLOTS 128
    >> +extern struct hlist_head smack_known_hash[SMACK_HASH_SLOTS];
    >> +
    >> /*
    >> * Is the directory transmuting?
    >> */
    >> diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
    >> index 6a0377f..b598c32 100644
    >> --- a/security/smack/smack_access.c
    >> +++ b/security/smack/smack_access.c
    >> @@ -325,6 +325,25 @@ void smack_log(char *subject_label, char *object_label, int request,
    >>
    >> DEFINE_MUTEX(smack_known_lock);
    >>
    >> +struct hlist_head smack_known_hash[SMACK_HASH_SLOTS];
    >> +
    >> +/**
    >> + * smk_insert_entry - insert a smack label into a hash map,
    >> + *
    >> + * this function must be called under smack_known_lock
    >> + */
    >> +void smk_insert_entry(struct smack_known *skp)
    >> +{
    >> + unsigned int hash;
    >> + struct hlist_head *head;
    >> +
    >> + hash = full_name_hash(skp->smk_known, strlen(skp->smk_known));
    >> + head = &smack_known_hash[hash & (SMACK_HASH_SLOTS - 1)];
    >> +
    >> + hlist_add_head_rcu(&skp->smk_hashed, head);
    >> + list_add_rcu(&skp->list, &smack_known_list);
    >> +}
    >> +
    >> /**
    >> * smk_find_entry - find a label on the list, return the list entry
    >> * @string: a text string that might be a Smack label
    >> @@ -334,12 +353,17 @@ DEFINE_MUTEX(smack_known_lock);
    >> */
    >> struct smack_known *smk_find_entry(const char *string)
    >> {
    >> + unsigned int hash;
    >> + struct hlist_head *head;
    >> + struct hlist_node *cursor;
    >> struct smack_known *skp;
    >>
    >> - list_for_each_entry_rcu(skp, &smack_known_list, list) {
    >> + hash = full_name_hash(string, strlen(string));
    >> + head = &smack_known_hash[hash & (SMACK_HASH_SLOTS - 1)];
    >> +
    >> + hlist_for_each_entry_rcu(skp, cursor, head, smk_hashed)
    >> if (strcmp(skp->smk_known, string) == 0)
    >> return skp;
    >> - }
    >>
    >> return NULL;
    >> }
    >> @@ -475,7 +499,7 @@ struct smack_known *smk_import_entry(const char *string, int len)
    >> * Make sure that the entry is actually
    >> * filled before putting it on the list.
    >> */
    >> - list_add_rcu(&skp->list, &smack_known_list);
    >> + smk_insert_entry(skp);
    >> goto unlockout;
    >> }
    >> /*
    >> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
    >> index 6a08330..6cabca6 100644
    >> --- a/security/smack/smack_lsm.c
    >> +++ b/security/smack/smack_lsm.c
    >> @@ -3868,12 +3868,12 @@ static __init void init_smack_known_list(void)
    >> /*
    >> * Create the known labels list
    >> */
    >> - list_add(&smack_known_huh.list, &smack_known_list);
    >> - list_add(&smack_known_hat.list, &smack_known_list);
    >> - list_add(&smack_known_star.list, &smack_known_list);
    >> - list_add(&smack_known_floor.list, &smack_known_list);
    >> - list_add(&smack_known_invalid.list, &smack_known_list);
    >> - list_add(&smack_known_web.list, &smack_known_list);
    >> + smk_insert_entry(&smack_known_huh);
    >> + smk_insert_entry(&smack_known_hat);
    >> + smk_insert_entry(&smack_known_star);
    >> + smk_insert_entry(&smack_known_floor);
    >> + smk_insert_entry(&smack_known_invalid);
    >> + smk_insert_entry(&smack_known_web);
    >> }
    >>
    >> /**
    > --
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