[PATCH] uml: fix exitcall ordering bug

This fixes an exitcall ordering bug - calls to ignore_sigio_fd can come from
exitcalls that come after the sigio thread has been killed.  This would cause
shutdown to hang or crash.

Fixed by having ignore_sigio_fd check that the thread is present before trying
to communicate with it.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 8 insertions, 1 deletions

diff --git a/arch/um/os-Linux/sigio.c b/arch/um/os-Linux/sigio.c
index 0d2422a7d72c..d22623e8fced 100644
--- a/arch/um/os-Linux/sigio.c
+++ b/arch/um/os-Linux/sigio.c
@@ -191,6 +191,13 @@ int ignore_sigio_fd(int fd)
         struct pollfd *p;
         int err = 0, i, n = 0;
 
+        /* This is called from exitcalls elsewhere in UML - if
+         * sigio_cleanup has already run, then update_thread will hang
+         * or fail because the thread is no longer running.
+         */
+        if(write_sigio_pid == -1)
+                return -EIO;
+
         sigio_lock();
         for(i = 0; i < current_poll.used; i++){
                 if(current_poll.poll[i].fd == fd) break;
@@ -215,7 +222,7 @@ int ignore_sigio_fd(int fd)
         update_thread();
  out:
         sigio_unlock();
-        return(err);
+        return err;
 }
 
 static struct pollfd *setup_initial_poll(int fd)