On Mon, Oct 13, 2025 at 4:17 PM Paul Moore <[email protected]> wrote: > > 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 >
Thank you for reviewing this one, Paul! And thanks a lot for your suggestions, I'll work on a v2 addressing those shortly.
