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audit: move the tree pruning to a dedicated thread

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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 <msw@amazon.com>
Cc: Matt Wilson <msw@amazon.com>
Signed-off-by: Imre Palik <imrep@amazon.de>
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <pmoore@redhat.com>
This commit is contained in:
Imre Palik 2015-02-23 15:37:59 -05:00 committed by Paul Moore
parent 2fded7f44b
commit f1aaf26224
1 changed files with 60 additions and 28 deletions
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88
kernel/audit_tree.c
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@ -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,