proc_lookupfd_common(): don't bother with instantiate unless the file is open

... and take the "check if file is open, pick ->f_mode" into a helper;
tid_fd_revalidate() can use it.

The next patch will get rid of tid_fd_revalidate() calls in instantiate
callbacks.

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

1 files changed, 34 insertions, 29 deletions

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 6b80cd1e419a..d38845ecc408 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -81,12 +81,29 @@ static const struct file_operations proc_fdinfo_file_operations = {
         .release        = single_release,
 };
 
+static bool tid_fd_mode(struct task_struct *task, unsigned fd, fmode_t *mode)
+{
+        struct files_struct *files = get_files_struct(task);
+        struct file *file;
+
+        if (!files)
+                return false;
+
+        rcu_read_lock();
+        file = fcheck_files(files, fd);
+        if (file)
+                *mode = file->f_mode;
+        rcu_read_unlock();
+        put_files_struct(files);
+        return !!file;
+}
+
 static int tid_fd_revalidate(struct dentry *dentry, unsigned int flags)
 {
-        struct files_struct *files;
         struct task_struct *task;
         struct inode *inode;
         unsigned int fd;
+        fmode_t f_mode;
 
         if (flags & LOOKUP_RCU)
                 return -ECHILD;
@@ -96,35 +113,20 @@ static int tid_fd_revalidate(struct dentry *dentry, unsigned int flags)
         fd = proc_fd(inode);
 
         if (task) {
-                files = get_files_struct(task);
-                if (files) {
-                        struct file *file;
-
-                        rcu_read_lock();
-                        file = fcheck_files(files, fd);
-                        if (file) {
-                                unsigned f_mode = file->f_mode;
-
-                                rcu_read_unlock();
-                                put_files_struct(files);
-
-                                task_dump_owner(task, 0, &inode->i_uid, &inode->i_gid);
-
-                                if (S_ISLNK(inode->i_mode)) {
-                                        unsigned i_mode = S_IFLNK;
-                                        if (f_mode & FMODE_READ)
-                                                i_mode |= S_IRUSR | S_IXUSR;
-                                        if (f_mode & FMODE_WRITE)
-                                                i_mode |= S_IWUSR | S_IXUSR;
-                                        inode->i_mode = i_mode;
-                                }
-
-                                security_task_to_inode(task, inode);
-                                put_task_struct(task);
-                                return 1;
+                if (tid_fd_mode(task, fd, &f_mode)) {
+                        task_dump_owner(task, 0, &inode->i_uid, &inode->i_gid);
+
+                        if (S_ISLNK(inode->i_mode)) {
+                                unsigned i_mode = S_IFLNK;
+                                if (f_mode & FMODE_READ)
+                                        i_mode |= S_IRUSR | S_IXUSR;
+                                if (f_mode & FMODE_WRITE)
+                                        i_mode |= S_IWUSR | S_IXUSR;
+                                inode->i_mode = i_mode;
                         }
-                        rcu_read_unlock();
-                        put_files_struct(files);
+                        security_task_to_inode(task, inode);
+                        put_task_struct(task);
+                        return 1;
                 }
                 put_task_struct(task);
         }
@@ -203,11 +205,14 @@ static struct dentry *proc_lookupfd_common(struct inode *dir,
         struct task_struct *task = get_proc_task(dir);
         int result = -ENOENT;
         unsigned fd = name_to_int(&dentry->d_name);
+        fmode_t f_mode;
 
         if (!task)
                 goto out_no_task;
         if (fd == ~0U)
                 goto out;
+        if (!tid_fd_mode(task, fd, &f_mode))
+                goto out;
 
         result = instantiate(dir, dentry, task, (void *)(unsigned long)fd);
 out: