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Diffstat (limited to 'fs/file.c')
-rw-r--r--fs/file.c72
1 files changed, 56 insertions, 16 deletions
diff --git a/fs/file.c b/fs/file.c
index ad4a8bf3cf10..97d212a9b814 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -841,28 +841,68 @@ void do_close_on_exec(struct files_struct *files)
spin_unlock(&files->file_lock);
}
-static struct file *__fget_files(struct files_struct *files, unsigned int fd,
- fmode_t mask, unsigned int refs)
+static inline struct file *__fget_files_rcu(struct files_struct *files,
+ unsigned int fd, fmode_t mask, unsigned int refs)
{
- struct file *file;
+ for (;;) {
+ struct file *file;
+ struct fdtable *fdt = rcu_dereference_raw(files->fdt);
+ struct file __rcu **fdentry;
- rcu_read_lock();
-loop:
- file = files_lookup_fd_rcu(files, fd);
- if (file) {
- /* File object ref couldn't be taken.
- * dup2() atomicity guarantee is the reason
- * we loop to catch the new file (or NULL pointer)
+ if (unlikely(fd >= fdt->max_fds))
+ return NULL;
+
+ fdentry = fdt->fd + array_index_nospec(fd, fdt->max_fds);
+ file = rcu_dereference_raw(*fdentry);
+ if (unlikely(!file))
+ return NULL;
+
+ if (unlikely(file->f_mode & mask))
+ return NULL;
+
+ /*
+ * Ok, we have a file pointer. However, because we do
+ * this all locklessly under RCU, we may be racing with
+ * that file being closed.
+ *
+ * Such a race can take two forms:
+ *
+ * (a) the file ref already went down to zero,
+ * and get_file_rcu_many() fails. Just try
+ * again:
*/
- if (file->f_mode & mask)
- file = NULL;
- else if (!get_file_rcu_many(file, refs))
- goto loop;
- else if (files_lookup_fd_raw(files, fd) != file) {
+ if (unlikely(!get_file_rcu_many(file, refs)))
+ continue;
+
+ /*
+ * (b) the file table entry has changed under us.
+ * Note that we don't need to re-check the 'fdt->fd'
+ * pointer having changed, because it always goes
+ * hand-in-hand with 'fdt'.
+ *
+ * If so, we need to put our refs and try again.
+ */
+ if (unlikely(rcu_dereference_raw(files->fdt) != fdt) ||
+ unlikely(rcu_dereference_raw(*fdentry) != file)) {
fput_many(file, refs);
- goto loop;
+ continue;
}
+
+ /*
+ * Ok, we have a ref to the file, and checked that it
+ * still exists.
+ */
+ return file;
}
+}
+
+static struct file *__fget_files(struct files_struct *files, unsigned int fd,
+ fmode_t mask, unsigned int refs)
+{
+ struct file *file;
+
+ rcu_read_lock();
+ file = __fget_files_rcu(files, fd, mask, refs);
rcu_read_unlock();
return file;