Re: [PATCH v2] audit: merge loops in __audit_inode_child()

On Oct 22, 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 | 39 +++++++++++++++++----------------------
>  1 file changed, 17 insertions(+), 22 deletions(-)
> 
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index d1966144bdfe..8cebc016d9eb 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -2416,41 +2416,36 @@ 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->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;

As mentioned in my feedback on your v1 patch, we can probably set
n->type equal to AUDIT_TYPE_PARENT without checking n->type first
as it we want this set to AUDIT_TYPE_PARENT regardless.

Please either fix this, or explain why it needs to be the way that it
is in your v2 patch.

>  			found_parent = n;
> -			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))
> +			if (found_child)
> +				break;
>  			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;
> -			break;
> +			if (found_parent)
> +				break;
>  		}
>  	}
>  
> -- 
> 2.51.0

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