[PATCH] namespaces: fix exit race by splitting exit

Fix exit race by splitting the nsproxy putting into two pieces.  First
piece reduces the nsproxy refcount.  If we dropped the last reference, then
it puts the mnt_ns, and returns the nsproxy as a hint to the caller.  Else
it returns NULL.  The second piece of exiting task namespaces sets
tsk->nsproxy to NULL, and drops the references to other namespaces and
frees the nsproxy only if an nsproxy was passed in.

A little awkward and should probably be reworked, but hopefully it fixes
the NFS oops.

Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Daniel Hokka Zakrisson <daniel@hozac.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 35401720635b..a5bf5329ff97 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -396,7 +396,7 @@ void daemonize(const char *name, ...)
         current->fs = fs;
         atomic_inc(&fs->count);
 
-        exit_task_namespaces(current);
+        put_and_finalize_nsproxy(current->nsproxy);
         current->nsproxy = init_task.nsproxy;
         get_task_namespaces(current);
 
@@ -853,6 +853,7 @@ static void exit_notify(struct task_struct *tsk)
 fastcall NORET_TYPE void do_exit(long code)
 {
         struct task_struct *tsk = current;
+        struct nsproxy *ns;
         int group_dead;
 
         profile_task_exit(tsk);
@@ -938,8 +939,9 @@ fastcall NORET_TYPE void do_exit(long code)
 
         tsk->exit_code = code;
         proc_exit_connector(tsk);
+        ns = preexit_task_namespaces(tsk);
         exit_notify(tsk);
-        exit_task_namespaces(tsk);
+        exit_task_namespaces(tsk, ns);
 #ifdef CONFIG_NUMA
         mpol_free(tsk->mempolicy);
         tsk->mempolicy = NULL;