staging: lustre: statahead: race in start/stop statahead

[cascardo/linux.git] / drivers / staging / lustre / lustre / llite / statahead.c

diff --git a/drivers/staging/lustre/lustre/llite/statahead.c b/drivers/staging/lustre/lustre/llite/statahead.c
index 92972d0..8cc0bfa 100644 (file)
--- a/drivers/staging/lustre/lustre/llite/statahead.c
+++ b/drivers/staging/lustre/lustre/llite/statahead.c
@@ -1509,7 +1509,24 @@ static int start_statahead_thread(struct inode *dir, struct dentry *dentry)
        CDEBUG(D_READA, "start statahead thread: sai %p, parent %pd\n",
               sai, parent);
 
+       /*
+        * if another process started statahead thread, or deauthorized current
+        * lli_opendir_key, don't start statahead.
+        */
+       spin_lock(&lli->lli_sa_lock);
+       if (unlikely(lli->lli_sai || lli->lli_opendir_key ||
+                    lli->lli_opendir_pid != current->pid)) {
+               spin_unlock(&lli->lli_sa_lock);
+
+               dput(parent);
+               iput(sai->sai_inode);
+               rc = -EAGAIN;
+               goto out;
+       }
        lli->lli_sai = sai;
+       spin_unlock(&lli->lli_sa_lock);
+
+       atomic_inc(&ll_i2sbi(parent->d_inode)->ll_sa_running);
 
        task = kthread_run(ll_statahead_thread, parent, "ll_sa_%u",
                           lli->lli_opendir_pid);
@@ -1518,9 +1535,12 @@ static int start_statahead_thread(struct inode *dir, struct dentry *dentry)
                rc = PTR_ERR(task);
                CERROR("cannot start ll_sa thread: rc = %d\n", rc);
                dput(parent);
-               lli->lli_opendir_key = NULL;
+
+               spin_lock(&lli->lli_sa_lock);
                thread_set_flags(thread, SVC_STOPPED);
                thread_set_flags(&sai->sai_agl_thread, SVC_STOPPED);
+               spin_unlock(&lli->lli_sa_lock);
+
                ll_sai_put(sai);
                LASSERT(!lli->lli_sai);
                return -EAGAIN;
@@ -1529,7 +1549,6 @@ static int start_statahead_thread(struct inode *dir, struct dentry *dentry)
        l_wait_event(thread->t_ctl_waitq,
                     thread_is_running(thread) || thread_is_stopped(thread),
                     &lwi);
-       atomic_inc(&ll_i2sbi(d_inode(parent))->ll_sa_running);
        ll_sai_put(sai);
 
        /*
@@ -1540,9 +1559,11 @@ static int start_statahead_thread(struct inode *dir, struct dentry *dentry)
 
 out:
        kfree(sai);
+       /*
+        * once we start statahead thread failed, disable statahead so
+        * subsequent won't waste time to try it.
+        */
        spin_lock(&lli->lli_sa_lock);
-       lli->lli_opendir_key = NULL;
-       lli->lli_opendir_pid = 0;
        lli->lli_sa_enabled = 0;
        spin_unlock(&lli->lli_sa_lock);