On 15/01/30, Imre Palik wrote: > From: "Palik, Imre" <im...@amazon.de> > > When file auditing is enabled, during a low memory situation, a memory > allocation with __GFP_FS can lead to pruning the inode cache. Which can, > in turn lead to audit_tree_freeing_mark() being called. This can call > audit_schedule_prune(), that tries to fork a pruning thread, and > waits until the thread is created. But forking needs memory, and the > memory allocations there are done with __GFP_FS. > > So we are waiting merrily for some __GFP_FS memory allocations to complete, > while holding some filesystem locks. This can take a while ... > > This patch creates a single thread for pruning the tree from > audit_add_tree_rule(), and thus avoids the deadlock that the on-demand > thread creation can cause. > > Reported-by: Matt Wilson <m...@amazon.com> > Cc: Matt Wilson <m...@amazon.com> > Signed-off-by: Imre Palik <im...@amazon.de>
Reviewed-by: Richard Guy Briggs <r...@redhat.com> > --- > kernel/audit_tree.c | 88 > +++++++++++++++++++++++++++++++++++---------------- > 1 file changed, 60 insertions(+), 28 deletions(-) > > diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c > index 2e0c974..71fd1f2 100644 > --- a/kernel/audit_tree.c > +++ b/kernel/audit_tree.c > @@ -37,6 +37,7 @@ struct audit_chunk { > > static LIST_HEAD(tree_list); > static LIST_HEAD(prune_list); > +static struct task_struct *prune_thread; > > /* > * One struct chunk is attached to each inode of interest. > @@ -651,6 +652,57 @@ static int tag_mount(struct vfsmount *mnt, void *arg) > return tag_chunk(mnt->mnt_root->d_inode, arg); > } > > +/* > + * That gets run when evict_chunk() ends up needing to kill audit_tree. > + * Runs from a separate thread. > + */ > +static int prune_tree_thread(void *unused) > +{ > + for (;;) { > + set_current_state(TASK_INTERRUPTIBLE); > + if (list_empty(&prune_list)) > + schedule(); > + __set_current_state(TASK_RUNNING); > + > + mutex_lock(&audit_cmd_mutex); > + mutex_lock(&audit_filter_mutex); > + > + while (!list_empty(&prune_list)) { > + struct audit_tree *victim; > + > + victim = list_entry(prune_list.next, > + struct audit_tree, list); > + list_del_init(&victim->list); > + > + mutex_unlock(&audit_filter_mutex); > + > + prune_one(victim); > + > + mutex_lock(&audit_filter_mutex); > + } > + > + mutex_unlock(&audit_filter_mutex); > + mutex_unlock(&audit_cmd_mutex); > + } > + return 0; > +} > + > +static int audit_launch_prune(void) > +{ > + if (prune_thread) > + return 0; > + prune_thread = kthread_create(prune_tree_thread, NULL, > + "audit_prune_tree"); > + if (IS_ERR(prune_thread)) { > + pr_err("cannot start thread audit_prune_tree"); > + prune_thread = NULL; > + return -ENOMEM; > + } else { > + wake_up_process(prune_thread); > + return 0; > + } > +} > + > /* called with audit_filter_mutex */ > int audit_add_tree_rule(struct audit_krule *rule) > { > @@ -674,6 +726,12 @@ int audit_add_tree_rule(struct audit_krule *rule) > /* do not set rule->tree yet */ > mutex_unlock(&audit_filter_mutex); > > + if (unlikely(!prune_thread)) { > + err = audit_launch_prune(); > + if (err) > + goto Err; > + } > + > err = kern_path(tree->pathname, 0, &path); > if (err) > goto Err; > @@ -811,36 +869,10 @@ int audit_tag_tree(char *old, char *new) > return failed; > } > > -/* > - * That gets run when evict_chunk() ends up needing to kill audit_tree. > - * Runs from a separate thread. > - */ > -static int prune_tree_thread(void *unused) > -{ > - mutex_lock(&audit_cmd_mutex); > - mutex_lock(&audit_filter_mutex); > - > - while (!list_empty(&prune_list)) { > - struct audit_tree *victim; > - > - victim = list_entry(prune_list.next, struct audit_tree, list); > - list_del_init(&victim->list); > - > - mutex_unlock(&audit_filter_mutex); > - > - prune_one(victim); > - > - mutex_lock(&audit_filter_mutex); > - } > - > - mutex_unlock(&audit_filter_mutex); > - mutex_unlock(&audit_cmd_mutex); > - return 0; > -} > > static void audit_schedule_prune(void) > { > - kthread_run(prune_tree_thread, NULL, "audit_prune_tree"); > + wake_up_process(prune_thread); > } > > /* > @@ -907,9 +939,9 @@ static void evict_chunk(struct audit_chunk *chunk) > for (n = 0; n < chunk->count; n++) > list_del_init(&chunk->owners[n].list); > spin_unlock(&hash_lock); > + mutex_unlock(&audit_filter_mutex); > if (need_prune) > audit_schedule_prune(); > - mutex_unlock(&audit_filter_mutex); > } > > static int audit_tree_handle_event(struct fsnotify_group *group, > -- > 1.7.9.5 > > -- > Linux-audit mailing list > linux-au...@redhat.com > https://www.redhat.com/mailman/listinfo/linux-audit - RGB -- Richard Guy Briggs <rbri...@redhat.com> Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat Remote, Ottawa, Canada Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/