splice: add helpers for locking pipe inode

There are lots of sequences like this, especially in splice code:

	if (pipe->inode)
		mutex_lock(&pipe->inode->i_mutex);
	/* do something */
	if (pipe->inode)
		mutex_unlock(&pipe->inode->i_mutex);

so introduce helpers which do the conditional locking and unlocking.
Also replace the inode_double_lock() call with a pipe_double_lock()
helper to avoid spreading the use of this functionality beyond the
pipe code.

This patch is just a cleanup, and should cause no behavioral changes.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

3 files changed, 59 insertions, 69 deletions

diff --git a/fs/inode.c b/fs/inode.c
index d06d6d268de9..6ad14a1cd8c9 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1470,42 +1470,6 @@ static void __wait_on_freeing_inode(struct inode *inode)
         spin_lock(&inode_lock);
 }
 
-/*
- * We rarely want to lock two inodes that do not have a parent/child
- * relationship (such as directory, child inode) simultaneously. The
- * vast majority of file systems should be able to get along fine
- * without this. Do not use these functions except as a last resort.
- */
-void inode_double_lock(struct inode *inode1, struct inode *inode2)
-{
-        if (inode1 == NULL || inode2 == NULL || inode1 == inode2) {
-                if (inode1)
-                        mutex_lock(&inode1->i_mutex);
-                else if (inode2)
-                        mutex_lock(&inode2->i_mutex);
-                return;
-        }
-
-        if (inode1 < inode2) {
-                mutex_lock_nested(&inode1->i_mutex, I_MUTEX_PARENT);
-                mutex_lock_nested(&inode2->i_mutex, I_MUTEX_CHILD);
-        } else {
-                mutex_lock_nested(&inode2->i_mutex, I_MUTEX_PARENT);
-                mutex_lock_nested(&inode1->i_mutex, I_MUTEX_CHILD);
-        }
-}
-EXPORT_SYMBOL(inode_double_lock);
-
-void inode_double_unlock(struct inode *inode1, struct inode *inode2)
-{
-        if (inode1)
-                mutex_unlock(&inode1->i_mutex);
-
-        if (inode2 && inode2 != inode1)
-                mutex_unlock(&inode2->i_mutex);
-}
-EXPORT_SYMBOL(inode_double_unlock);
-
 static __initdata unsigned long ihash_entries;
 static int __init set_ihash_entries(char *str)
 {
diff --git a/fs/pipe.c b/fs/pipe.c
index 4af7aa521813..13414ec45b8d 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -37,6 +37,42 @@
  * -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
  */
 
+static void pipe_lock_nested(struct pipe_inode_info *pipe, int subclass)
+{
+        if (pipe->inode)
+                mutex_lock_nested(&pipe->inode->i_mutex, subclass);
+}
+
+void pipe_lock(struct pipe_inode_info *pipe)
+{
+        /*
+         * pipe_lock() nests non-pipe inode locks (for writing to a file)
+         */
+        pipe_lock_nested(pipe, I_MUTEX_PARENT);
+}
+EXPORT_SYMBOL(pipe_lock);
+
+void pipe_unlock(struct pipe_inode_info *pipe)
+{
+        if (pipe->inode)
+                mutex_unlock(&pipe->inode->i_mutex);
+}
+EXPORT_SYMBOL(pipe_unlock);
+
+void pipe_double_lock(struct pipe_inode_info *pipe1,
+                      struct pipe_inode_info *pipe2)
+{
+        BUG_ON(pipe1 == pipe2);
+
+        if (pipe1 < pipe2) {
+                pipe_lock_nested(pipe1, I_MUTEX_PARENT);
+                pipe_lock_nested(pipe2, I_MUTEX_CHILD);
+        } else {
+                pipe_lock_nested(pipe2, I_MUTEX_CHILD);
+                pipe_lock_nested(pipe1, I_MUTEX_PARENT);
+        }
+}
+
 /* Drop the inode semaphore and wait for a pipe event, atomically */
 void pipe_wait(struct pipe_inode_info *pipe)
 {
@@ -47,12 +83,10 @@ void pipe_wait(struct pipe_inode_info *pipe)
          * is considered a noninteractive wait:
          */
         prepare_to_wait(&pipe->wait, &wait, TASK_INTERRUPTIBLE);
-        if (pipe->inode)
-                mutex_unlock(&pipe->inode->i_mutex);
+        pipe_unlock(pipe);
         schedule();
         finish_wait(&pipe->wait, &wait);
-        if (pipe->inode)
-                mutex_lock(&pipe->inode->i_mutex);
+        pipe_lock(pipe);
 }
 
 static int
diff --git a/fs/splice.c b/fs/splice.c
index 128ee36a719b..5384a90665d0 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -182,8 +182,7 @@ ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
         do_wakeup = 0;
         page_nr = 0;
 
-        if (pipe->inode)
-                mutex_lock(&pipe->inode->i_mutex);
+        pipe_lock(pipe);
 
         for (;;) {
                 if (!pipe->readers) {
@@ -245,15 +244,13 @@ ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
                 pipe->waiting_writers--;
         }
 
-        if (pipe->inode) {
-                mutex_unlock(&pipe->inode->i_mutex);
+        pipe_unlock(pipe);
 
-                if (do_wakeup) {
-                        smp_mb();
-                        if (waitqueue_active(&pipe->wait))
-                                wake_up_interruptible(&pipe->wait);
-                        kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
-                }
+        if (do_wakeup) {
+                smp_mb();
+                if (waitqueue_active(&pipe->wait))
+                        wake_up_interruptible(&pipe->wait);
+                kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
         }
 
         while (page_nr < spd_pages)
@@ -801,11 +798,9 @@ ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
                 .u.file = out,
         };
 
-        if (pipe->inode)
-                mutex_lock(&pipe->inode->i_mutex);
+        pipe_lock(pipe);
         ret = __splice_from_pipe(pipe, &sd, actor);
-        if (pipe->inode)
-                mutex_unlock(&pipe->inode->i_mutex);
+        pipe_unlock(pipe);
 
         return ret;
 }
@@ -837,8 +832,7 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
         };
         ssize_t ret;
 
-        if (pipe->inode)
-                mutex_lock_nested(&pipe->inode->i_mutex, I_MUTEX_PARENT);
+        pipe_lock(pipe);
 
         splice_from_pipe_begin(&sd);
         do {
@@ -854,8 +848,7 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
         } while (ret > 0);
         splice_from_pipe_end(pipe, &sd);
 
-        if (pipe->inode)
-                mutex_unlock(&pipe->inode->i_mutex);
+        pipe_unlock(pipe);
 
         if (sd.num_spliced)
                 ret = sd.num_spliced;
@@ -1348,8 +1341,7 @@ static long vmsplice_to_user(struct file *file, const struct iovec __user *iov,
         if (!pipe)
                 return -EBADF;
 
-        if (pipe->inode)
-                mutex_lock(&pipe->inode->i_mutex);
+        pipe_lock(pipe);
 
         error = ret = 0;
         while (nr_segs) {
@@ -1404,8 +1396,7 @@ static long vmsplice_to_user(struct file *file, const struct iovec __user *iov,
                 iov++;
         }
 
-        if (pipe->inode)
-                mutex_unlock(&pipe->inode->i_mutex);
+        pipe_unlock(pipe);
 
         if (!ret)
                 ret = error;
@@ -1533,7 +1524,7 @@ static int link_ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
                 return 0;
 
         ret = 0;
-        mutex_lock(&pipe->inode->i_mutex);
+        pipe_lock(pipe);
 
         while (!pipe->nrbufs) {
                 if (signal_pending(current)) {
@@ -1551,7 +1542,7 @@ static int link_ipipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
                 pipe_wait(pipe);
         }
 
-        mutex_unlock(&pipe->inode->i_mutex);
+        pipe_unlock(pipe);
         return ret;
 }
 
@@ -1571,7 +1562,7 @@ static int link_opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
                 return 0;
 
         ret = 0;
-        mutex_lock(&pipe->inode->i_mutex);
+        pipe_lock(pipe);
 
         while (pipe->nrbufs >= PIPE_BUFFERS) {
                 if (!pipe->readers) {
@@ -1592,7 +1583,7 @@ static int link_opipe_prep(struct pipe_inode_info *pipe, unsigned int flags)
                 pipe->waiting_writers--;
         }
 
-        mutex_unlock(&pipe->inode->i_mutex);
+        pipe_unlock(pipe);
         return ret;
 }
 
@@ -1608,10 +1599,10 @@ static int link_pipe(struct pipe_inode_info *ipipe,
 
         /*
          * Potential ABBA deadlock, work around it by ordering lock
-         * grabbing by inode address. Otherwise two different processes
+         * grabbing by pipe info address. Otherwise two different processes
          * could deadlock (one doing tee from A -> B, the other from B -> A).
          */
-        inode_double_lock(ipipe->inode, opipe->inode);
+        pipe_double_lock(ipipe, opipe);
 
         do {
                 if (!opipe->readers) {
@@ -1662,7 +1653,8 @@ static int link_pipe(struct pipe_inode_info *ipipe,
         if (!ret && ipipe->waiting_writers && (flags & SPLICE_F_NONBLOCK))
                 ret = -EAGAIN;
 
-        inode_double_unlock(ipipe->inode, opipe->inode);
+        pipe_unlock(ipipe);
+        pipe_unlock(opipe);
 
         /*
          * If we put data in the output pipe, wakeup any potential readers.