diff options
-rw-r--r-- | fs/file.c | 72 |
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; |