On 2026-02-06 15:19, Waiman Long wrote: > When the audit subsystem is enabled, it can do a lot of get_fs_pwd() > calls to get references to fs->pwd and then releasing those references > back with path_put() later. That may cause a lot of spinlock contention > on a single pwd's dentry lock because of the constant changes to the > reference count when there are many processes on the same working > directory actively doing open/close system calls. This can cause > noticeable performance regresssion when compared with the case where > the audit subsystem is turned off especially on systems with a lot of > CPUs which is becoming more common these days. > > To avoid this kind of performance regression, use the new > get_fs_pwd_pool() and put_fs_pwd_pool() APIs to acquire and release a > fs->pwd reference. This should greatly reduce the number of path_get() > and path_put() calls that are needed. > > After installing a test kernel with auditing enabled and counters > added to track the get_fs_pwd_pool() and put_fs_pwd_pool() calls on > a 2-socket 96-core test system and running a parallel kernel build, > the counter values for this particular test run were shown below. > > fs_get_path=307,903 > fs_get_pool=56,583,192 > fs_put_path=6,209 > fs_put_pool=56,885,147 > > Of the about 57M calls to get_fs_pwd_pool() and put_fs_pwd_pool(), the > majority of them are just updating the pwd_refs counters. Only less than > 1% of those calls require an actual path_get() and path_put() calls. The > difference between fs_get_path and fs_put_path represents the extra pwd > references that were still stored in various active task->fs's when the > counter values were retrieved. > > It can be seen that the number of path_get() and path_put() calls are > reduced by quite a lot. > > Signed-off-by: Waiman Long <[email protected]>
Reviewed-by: Richard Guy Briggs <[email protected]> > --- > kernel/auditsc.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c > index dd0563a8e0be..af22f8be4d70 100644 > --- a/kernel/auditsc.c > +++ b/kernel/auditsc.c > @@ -931,6 +931,9 @@ static inline void audit_free_names(struct audit_context > *context) > { > struct audit_names *n, *next; > > + if (!context->name_count) > + return; /* audit_alloc_name() has not been called */ > + > list_for_each_entry_safe(n, next, &context->names_list, list) { > list_del(&n->list); > if (n->name) > @@ -939,7 +942,7 @@ static inline void audit_free_names(struct audit_context > *context) > kfree(n); > } > context->name_count = 0; > - path_put(&context->pwd); > + put_fs_pwd_pool(current->fs, &context->pwd); > context->pwd.dentry = NULL; > context->pwd.mnt = NULL; > } > @@ -2165,7 +2168,7 @@ static struct audit_names *audit_alloc_name(struct > audit_context *context, > > context->name_count++; > if (!context->pwd.dentry) > - get_fs_pwd(current->fs, &context->pwd); > + get_fs_pwd_pool(current->fs, &context->pwd); > return aname; > } > > -- > 2.52.0 > - RGB -- Richard Guy Briggs <[email protected]> Sr. S/W Engineer, Kernel Security, Base Operating Systems Remote, Ottawa, Red Hat Canada Upstream IRC: SunRaycer Voice: +1.613.860 2354 SMS: +1.613.518.6570
