On Sep 4, 2025 Ricardo Robaina <[email protected]> wrote:
>
> Whenever there's audit context, __audit_inode_child() gets called
> numerous times, which can lead to high latency in scenarios that
> create too many sysfs/debugfs entries at once, for instance, upon
> device_add_disk() invocation.
>
> # uname -r
> 6.17.0-rc3+
>
> # auditctl -a always,exit -F path=/tmp -k foo
> # time insmod loop max_loop=1000
> real 0m42.753s
> user 0m0.000s
> sys 0m42.494s
>
> # perf record -a insmod loop max_loop=1000
> # perf report --stdio |grep __audit_inode_child
> 37.95% insmod [kernel.kallsyms] [k] __audit_inode_child
>
> __audit_inode_child() searches for both the parent and the child
> in two different loops that iterate over the same list. This
> process can be optimized by merging these into a single loop,
> without changing the function behavior or affecting the code's
> readability.
>
> This patch merges the two loops that walk through the list
> context->names_list into a single loop. This optimization resulted
> in around 54% performance enhancement for the benchmark.
>
> # uname -r
> 6.17.0-rc3+-enhanced
>
> # auditctl -a always,exit -F path=/tmp -k foo
> # time insmod loop max_loop=1000
> real 0m19.388s
> user 0m0.000s
> sys 0m19.149s
>
> Signed-off-by: Ricardo Robaina <[email protected]>
> ---
> kernel/auditsc.c | 40 ++++++++++++++++++----------------------
> 1 file changed, 18 insertions(+), 22 deletions(-)
Thanks Ricardo, that's a nice improvement! I saw a few additional things
that could help simplify the code and possibly speed things up a bit
more, see my comments below.
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index eb98cd6fe91f..7abfb68687fb 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -2437,44 +2437,40 @@ void __audit_inode_child(struct inode *parent,
> if (inode)
> handle_one(inode);
>
> - /* look for a parent entry first */
> list_for_each_entry(n, &context->names_list, list) {
> - if (!n->name ||
> - (n->type != AUDIT_TYPE_PARENT &&
> - n->type != AUDIT_TYPE_UNKNOWN))
> + /* can only match entries that have a name */
> + if (!n->name)
> continue;
>
> - if (n->ino == parent->i_ino && n->dev == parent->i_sb->s_dev &&
> - !audit_compare_dname_path(dname,
> - n->name->name, n->name_len)) {
> + /* look for a parent entry first */
> + if (!found_parent &&
> + (n->type == AUDIT_TYPE_PARENT || n->type ==
> AUDIT_TYPE_UNKNOWN) &&
> + (n->ino == parent->i_ino && n->dev == parent->i_sb->s_dev &&
> + !audit_compare_dname_path(dname, n->name->name,
> n->name_len))) {
> if (n->type == AUDIT_TYPE_UNKNOWN)
> n->type = AUDIT_TYPE_PARENT;
We probably don't need to check 'n->type' first, as we want it to always
be set to AUDIT_TYPE_PARENT regardless of it's current value.
> found_parent = n;
We can probably 'continue' here since a match can't be both a parent and
a child at the same time.
Similarly, if we add move the 'if (found_parent && found_child)' check
up to here we don't need to run it on every pass through the loop, just
when we find a match.
Taking the two comment above into account, I would imagine something like
this would good:
found_parent = n;
if (found_child)
break;
continue;
> - break;
> }
> - }
>
> - cond_resched();
> -
> - /* is there a matching child entry? */
> - list_for_each_entry(n, &context->names_list, list) {
> - /* can only match entries that have a name */
> - if (!n->name ||
> - (n->type != type && n->type != AUDIT_TYPE_UNKNOWN))
> - continue;
> -
> - if (!strcmp(dname->name, n->name->name) ||
> - !audit_compare_dname_path(dname, n->name->name,
> + /* is there a matching child entry? */
> + if (!found_child &&
> + (n->type == type || n->type == AUDIT_TYPE_UNKNOWN) &&
> + (!strcmp(dname->name, n->name->name) ||
> + !audit_compare_dname_path(dname, n->name->name,
> found_parent ?
> found_parent->name_len :
> - AUDIT_NAME_FULL)) {
> + AUDIT_NAME_FULL))) {
> if (n->type == AUDIT_TYPE_UNKNOWN)
> n->type = type;
> found_child = n;
Similar to the parent case above, let's check to see if both a parent and
a child have been found. We can probably skip the 'continue' here are we
are at the end of the loop.
found_child = n;
if (found_parent)
break;
> - break;
> }
> +
> + if (found_parent && found_child)
> + break;
> }
>
> + cond_resched();
The 'cond_resched()' call was located between the two loops to help avoid
a soft lockup caused by running through both loops; since we are now
condensing that into one loop we can probably drop the 'cond_resched()'
call ... which is definitely a good thing as it was a bit of a hack, a
necessary hack, but still a hack :)
> if (!found_parent) {
> /* create a new, "anonymous" parent record */
> n = audit_alloc_name(context, AUDIT_TYPE_PARENT);
> --
> 2.51.0
--
paul-moore.com
