pipe: take allocation and freeing of pipe_inode_info out of ->i_mutex

* new field - pipe->files; number of struct file over that pipe (all
  sharing the same inode, of course); protected by inode->i_lock.
* pipe_release() decrements pipe->files, clears inode->i_pipe when
  if the counter has reached 0 (all under ->i_lock) and, in that case,
  frees pipe after having done pipe_unlock()
* fifo_open() starts with grabbing ->i_lock, and either bumps pipe->files
  if ->i_pipe was non-NULL or allocates a new pipe (dropping and regaining
  ->i_lock) and rechecks ->i_pipe; if it's still NULL, inserts new pipe
  there, otherwise bumps ->i_pipe->files and frees the one we'd allocated.
  At that point we know that ->i_pipe is non-NULL and won't go away, so
  we can do pipe_lock() on it and proceed as we used to.  If we end up
  failing, decrement pipe->files and if it reaches 0 clear ->i_pipe and
  free the sucker after pipe_unlock().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 51 insertions, 21 deletions

diff --git a/fs/pipe.c b/fs/pipe.c
index 357471db890d..abaa9234d27b 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -718,23 +718,30 @@ pipe_poll(struct file *filp, poll_table *wait)
 static int
 pipe_release(struct inode *inode, struct file *file)
 {
-        struct pipe_inode_info *pipe;
+        struct pipe_inode_info *pipe = inode->i_pipe;
+        int kill = 0;
 
-        mutex_lock(&inode->i_mutex);
-        pipe = inode->i_pipe;
+        pipe_lock(pipe);
         if (file->f_mode & FMODE_READ)
                 pipe->readers--;
         if (file->f_mode & FMODE_WRITE)
                 pipe->writers--;
 
-        if (!pipe->readers && !pipe->writers) {
-                free_pipe_info(inode);
-        } else {
+        if (pipe->readers || pipe->writers) {
                 wake_up_interruptible_sync_poll(&pipe->wait, POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM | POLLERR | POLLHUP);
                 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
                 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
         }
-        mutex_unlock(&inode->i_mutex);
+        spin_lock(&inode->i_lock);
+        if (!--pipe->files) {
+                inode->i_pipe = NULL;
+                kill = 1;
+        }
+        spin_unlock(&inode->i_lock);
+        pipe_unlock(pipe);
+
+        if (kill)
+                __free_pipe_info(pipe);
 
         return 0;
 }
@@ -827,8 +834,9 @@ static struct inode * get_pipe_inode(void)
         pipe = alloc_pipe_info(inode);
         if (!pipe)
                 goto fail_iput;
-        inode->i_pipe = pipe;
 
+        inode->i_pipe = pipe;
+        pipe->files = 2;
         pipe->readers = pipe->writers = 1;
         inode->i_fop = &pipefifo_fops;
 
@@ -999,18 +1007,36 @@ static int fifo_open(struct inode *inode, struct file *filp)
 {
         struct pipe_inode_info *pipe;
         bool is_pipe = inode->i_sb->s_magic == PIPEFS_MAGIC;
+        int kill = 0;
         int ret;
 
-        mutex_lock(&inode->i_mutex);
-        pipe = inode->i_pipe;
-        if (!pipe) {
-                ret = -ENOMEM;
+        filp->f_version = 0;
+
+        spin_lock(&inode->i_lock);
+        if (inode->i_pipe) {
+                pipe = inode->i_pipe;
+                pipe->files++;
+                spin_unlock(&inode->i_lock);
+        } else {
+                spin_unlock(&inode->i_lock);
                 pipe = alloc_pipe_info(inode);
                 if (!pipe)
-                        goto err_nocleanup;
-                inode->i_pipe = pipe;
+                        return -ENOMEM;
+                pipe->files = 1;
+                spin_lock(&inode->i_lock);
+                if (unlikely(inode->i_pipe)) {
+                        inode->i_pipe->files++;
+                        spin_unlock(&inode->i_lock);
+                        __free_pipe_info(pipe);
+                        pipe = inode->i_pipe;
+                } else {
+                        inode->i_pipe = pipe;
+                        spin_unlock(&inode->i_lock);
+                }
         }
-        filp->f_version = 0;
+        /* OK, we have a pipe and it's pinned down */
+
+        pipe_lock(pipe);
 
         /* We can only do regular read/write on fifos */
         filp->f_mode &= (FMODE_READ | FMODE_WRITE);
@@ -1080,7 +1106,7 @@ static int fifo_open(struct inode *inode, struct file *filp)
         }
 
         /* Ok! */
-        mutex_unlock(&inode->i_mutex);
+        pipe_unlock(pipe);
         return 0;
 
 err_rd:
@@ -1096,11 +1122,15 @@ err_wr:
         goto err;
 
 err:
-        if (!pipe->readers && !pipe->writers)
-                free_pipe_info(inode);
-
-err_nocleanup:
-        mutex_unlock(&inode->i_mutex);
+        spin_lock(&inode->i_lock);
+        if (!--pipe->files) {
+                inode->i_pipe = NULL;
+                kill = 1;
+        }
+        spin_unlock(&inode->i_lock);
+        pipe_unlock(pipe);
+        if (kill)
+                __free_pipe_info(pipe);
         return ret;
 }