Walter Harms pointed out the locking was rather obtuse in dupfd. This
patch makes it much clearer.
diff -urpNX dontdiff linux-2.5.49/fs/fcntl.c linux-2.5.49-flock/fs/fcntl.c
--- linux-2.5.49/fs/fcntl.c 2002-10-16 05:21:24.000000000 -0700
+++ linux-2.5.49-flock/fs/fcntl.c 2002-11-24 10:14:09.000000000 -0800
@@ -75,8 +75,8 @@ static int expand_files(struct files_str
/*
* locate_fd finds a free file descriptor in the open_fds fdset,
- * expanding the fd arrays if necessary. The files write lock will be
- * held on exit to ensure that the fd can be entered atomically.
+ * expanding the fd arrays if necessary. Must be called with the
+ * file_lock held for write.
*/
static int locate_fd(struct files_struct *files,
@@ -86,8 +86,6 @@ static int locate_fd(struct files_struct
int error;
int start;
- write_lock(&files->file_lock);
-
error = -EINVAL;
if (orig_start >= current->rlim[RLIMIT_NOFILE].rlim_cur)
goto out;
@@ -131,30 +129,24 @@ out:
return error;
}
-static inline void allocate_fd(struct files_struct *files,
- struct file *file, int fd)
-{
- FD_SET(fd, files->open_fds);
- FD_CLR(fd, files->close_on_exec);
- write_unlock(&files->file_lock);
- fd_install(fd, file);
-}
-
static int dupfd(struct file *file, int start)
{
struct files_struct * files = current->files;
- int ret;
+ int fd;
- ret = locate_fd(files, file, start);
- if (ret < 0)
- goto out_putf;
- allocate_fd(files, file, ret);
- return ret;
+ write_lock(&files->file_lock);
+ fd = locate_fd(files, file, start);
+ if (fd >= 0) {
+ FD_SET(fd, files->open_fds);
+ FD_CLR(fd, files->close_on_exec);
+ write_unlock(&files->file_lock);
+ fd_install(fd, file);
+ } else {
+ write_unlock(&files->file_lock);
+ fput(file);
+ }
-out_putf:
- write_unlock(&files->file_lock);
- fput(file);
- return ret;
+ return fd;
}
asmlinkage long sys_dup2(unsigned int oldfd, unsigned int newfd)
--
"It's not Hollywood. War is real, war is primarily not about defeat or
victory, it is about death. I've seen thousands and thousands of dead bodies.
Do you think I want to have an academic debate on this subject?" -- Robert Fisk