Merge branch 'locks' of git://linux-nfs.org/~bfields/linux

* 'locks' of git://linux-nfs.org/~bfields/linux:
  pid-namespaces-vs-locks-interaction
  file locks: Use wait_event_interruptible_timeout()
  locks: clarify posix_locks_deadlock

2 files changed, 65 insertions, 61 deletions

diff --git a/fs/locks.c b/fs/locks.c
index 8b8388eca05e..49354b9c7dc1 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -125,6 +125,7 @@
 #include <linux/syscalls.h>
 #include <linux/time.h>
 #include <linux/rcupdate.h>
+#include <linux/pid_namespace.h>
 
 #include <asm/semaphore.h>
 #include <asm/uaccess.h>
@@ -185,6 +186,7 @@ void locks_init_lock(struct file_lock *fl)
         fl->fl_fasync = NULL;
         fl->fl_owner = NULL;
         fl->fl_pid = 0;
+        fl->fl_nspid = NULL;
         fl->fl_file = NULL;
         fl->fl_flags = 0;
         fl->fl_type = 0;
@@ -553,6 +555,8 @@ static void locks_insert_lock(struct file_lock **pos, struct file_lock *fl)
 {
         list_add(&fl->fl_link, &file_lock_list);
 
+        fl->fl_nspid = get_pid(task_tgid(current));
+
         /* insert into file's list */
         fl->fl_next = *pos;
         *pos = fl;
@@ -584,6 +588,11 @@ static void locks_delete_lock(struct file_lock **thisfl_p)
         if (fl->fl_ops && fl->fl_ops->fl_remove)
                 fl->fl_ops->fl_remove(fl);
 
+        if (fl->fl_nspid) {
+                put_pid(fl->fl_nspid);
+                fl->fl_nspid = NULL;
+        }
+
         locks_wake_up_blocks(fl);
         locks_free_lock(fl);
 }
@@ -634,33 +643,6 @@ static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *s
         return (locks_conflict(caller_fl, sys_fl));
 }
 
-static int interruptible_sleep_on_locked(wait_queue_head_t *fl_wait, int timeout)
-{
-        int result = 0;
-        DECLARE_WAITQUEUE(wait, current);
-
-        __set_current_state(TASK_INTERRUPTIBLE);
-        add_wait_queue(fl_wait, &wait);
-        if (timeout == 0)
-                schedule();
-        else
-                result = schedule_timeout(timeout);
-        if (signal_pending(current))
-                result = -ERESTARTSYS;
-        remove_wait_queue(fl_wait, &wait);
-        __set_current_state(TASK_RUNNING);
-        return result;
-}
-
-static int locks_block_on_timeout(struct file_lock *blocker, struct file_lock *waiter, int time)
-{
-        int result;
-        locks_insert_block(blocker, waiter);
-        result = interruptible_sleep_on_locked(&waiter->fl_wait, time);
-        __locks_delete_block(waiter);
-        return result;
-}
-
 void
 posix_test_lock(struct file *filp, struct file_lock *fl)
 {
@@ -673,55 +655,67 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
                 if (posix_locks_conflict(fl, cfl))
                         break;
         }
-        if (cfl)
+        if (cfl) {
                 __locks_copy_lock(fl, cfl);
-        else
+                if (cfl->fl_nspid)
+                        fl->fl_pid = pid_nr_ns(cfl->fl_nspid,
+                                                task_active_pid_ns(current));
+        } else
                 fl->fl_type = F_UNLCK;
         unlock_kernel();
         return;
 }
-
 EXPORT_SYMBOL(posix_test_lock);
 
-/* This function tests for deadlock condition before putting a process to
- * sleep. The detection scheme is no longer recursive. Recursive was neat,
- * but dangerous - we risked stack corruption if the lock data was bad, or
- * if the recursion was too deep for any other reason.
+/*
+ * Deadlock detection:
+ *
+ * We attempt to detect deadlocks that are due purely to posix file
+ * locks.
  *
- * We rely on the fact that a task can only be on one lock's wait queue
- * at a time. When we find blocked_task on a wait queue we can re-search
- * with blocked_task equal to that queue's owner, until either blocked_task
- * isn't found, or blocked_task is found on a queue owned by my_task.
+ * We assume that a task can be waiting for at most one lock at a time.
+ * So for any acquired lock, the process holding that lock may be
+ * waiting on at most one other lock.  That lock in turns may be held by
+ * someone waiting for at most one other lock.  Given a requested lock
+ * caller_fl which is about to wait for a conflicting lock block_fl, we
+ * follow this chain of waiters to ensure we are not about to create a
+ * cycle.
  *
- * Note: the above assumption may not be true when handling lock requests
- * from a broken NFS client. But broken NFS clients have a lot more to
- * worry about than proper deadlock detection anyway... --okir
+ * Since we do this before we ever put a process to sleep on a lock, we
+ * are ensured that there is never a cycle; that is what guarantees that
+ * the while() loop in posix_locks_deadlock() eventually completes.
  *
- * However, the failure of this assumption (also possible in the case of
- * multiple tasks sharing the same open file table) also means there's no
- * guarantee that the loop below will terminate.  As a hack, we give up
- * after a few iterations.
+ * Note: the above assumption may not be true when handling lock
+ * requests from a broken NFS client. It may also fail in the presence
+ * of tasks (such as posix threads) sharing the same open file table.
+ *
+ * To handle those cases, we just bail out after a few iterations.
  */
 
 #define MAX_DEADLK_ITERATIONS 10
 
+/* Find a lock that the owner of the given block_fl is blocking on. */
+static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl)
+{
+        struct file_lock *fl;
+
+        list_for_each_entry(fl, &blocked_list, fl_link) {
+                if (posix_same_owner(fl, block_fl))
+                        return fl->fl_next;
+        }
+        return NULL;
+}
+
 static int posix_locks_deadlock(struct file_lock *caller_fl,
                                 struct file_lock *block_fl)
 {
-        struct file_lock *fl;
         int i = 0;
 
-next_task:
-        if (posix_same_owner(caller_fl, block_fl))
-                return 1;
-        list_for_each_entry(fl, &blocked_list, fl_link) {
-                if (posix_same_owner(fl, block_fl)) {
-                        if (i++ > MAX_DEADLK_ITERATIONS)
-                                return 0;
-                        fl = fl->fl_next;
-                        block_fl = fl;
-                        goto next_task;
-                }
+        while ((block_fl = what_owner_is_waiting_for(block_fl))) {
+                if (i++ > MAX_DEADLK_ITERATIONS)
+                        return 0;
+                if (posix_same_owner(caller_fl, block_fl))
+                        return 1;
         }
         return 0;
 }
@@ -1256,7 +1250,10 @@ restart:
                 if (break_time == 0)
                         break_time++;
         }
-        error = locks_block_on_timeout(flock, new_fl, break_time);
+        locks_insert_block(flock, new_fl);
+        error = wait_event_interruptible_timeout(new_fl->fl_wait,
+                                                !new_fl->fl_next, break_time);
+        __locks_delete_block(new_fl);
         if (error >= 0) {
                 if (error == 0)
                         time_out_leases(inode);
@@ -2084,6 +2081,12 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
                                                         int id, char *pfx)
 {
         struct inode *inode = NULL;
+        unsigned int fl_pid;
+
+        if (fl->fl_nspid)
+                fl_pid = pid_nr_ns(fl->fl_nspid, task_active_pid_ns(current));
+        else
+                fl_pid = fl->fl_pid;
 
         if (fl->fl_file != NULL)
                 inode = fl->fl_file->f_path.dentry->d_inode;
@@ -2124,16 +2127,16 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
         }
         if (inode) {
 #ifdef WE_CAN_BREAK_LSLK_NOW
-                seq_printf(f, "%d %s:%ld ", fl->fl_pid,
+                seq_printf(f, "%d %s:%ld ", fl_pid,
                                 inode->i_sb->s_id, inode->i_ino);
 #else
                 /* userspace relies on this representation of dev_t ;-( */
-                seq_printf(f, "%d %02x:%02x:%ld ", fl->fl_pid,
+                seq_printf(f, "%d %02x:%02x:%ld ", fl_pid,
                                 MAJOR(inode->i_sb->s_dev),
                                 MINOR(inode->i_sb->s_dev), inode->i_ino);
 #endif
         } else {
-                seq_printf(f, "%d <none>:0 ", fl->fl_pid);
+                seq_printf(f, "%d <none>:0 ", fl_pid);
         }
         if (IS_POSIX(fl)) {
                 if (fl->fl_end == OFFSET_MAX)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a516b6716870..b7736ab8bb5e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -872,6 +872,7 @@ struct file_lock {
         struct list_head fl_block;      /* circular list of blocked processes */
         fl_owner_t fl_owner;
         unsigned int fl_pid;
+        struct pid *fl_nspid;
         wait_queue_head_t fl_wait;
         struct file *fl_file;
         unsigned char fl_flags;