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Commit f1aaf262 authored by Imre Palik's avatar Imre Palik Committed by Paul Moore
Browse files

audit: move the tree pruning to a dedicated thread 



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: default avatarMatt Wilson <msw@amazon.com>
Cc: Matt Wilson <msw@amazon.com>
Signed-off-by: default avatarImre Palik <imrep@amazon.de>
Reviewed-by: default avatarRichard Guy Briggs <rgb@redhat.com>
Signed-off-by: default avatarPaul Moore <pmoore@redhat.com>
parent 2fded7f4

kernel/audit_tree.c

+60 −28
Original line number Diff line number Diff line
@@ -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,