[PATCH] ptmx: fix duplicate idr_remove

Remove duplicate call to idr_remove() in ptmx_open.

Error during open can result in call to release_dev() followed by call to
idr_remove().  release_dev already calls idr_remove so the second call can
cause a stack dump in idr_remove()->sub_remove() flagging an attempt to
release an already released entry.

I reproduces this on a machine with a misconfigured X server (attempting to
restart multiple times rapidly) getting the same error as the 1st link
below.

This also seems to be related to:
http://marc.theaimsgroup.com/?l=selinux&m=110536513426735&w=2
http://marc.theaimsgroup.com/?l=selinux&m=110596994916785&w=2

The stack dump can occur on close (as well as open) as shown
in the 1st instance above, possible from something like:

process A - open (index=0), open fail to out1,
  release_dev calls idr_remove (index 0), down(sem) sleeps
process B - open (index=0), open OK (idr allocated)
process A - wake and call idr_remove on index 0
...
process B - close, release_dev, stack dump on idr_remove (index=0)
  because entry already removed

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 6f58cacec341..b1f9a1582dd7 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -2195,6 +2195,7 @@ static int ptmx_open(struct inode * inode, struct file * filp)
                 return 0;
 out1:
         release_dev(filp);
+        return retval;
 out:
         down(&allocated_ptys_lock);
         idr_remove(&allocated_ptys, index);