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[PATCH] namespaces: fix exit race by splitting exit

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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>
This commit is contained in:
Serge E. Hallyn 2007-01-29 13:19:40 -08:00 committed by Linus Torvalds
parent c0d4d573fe
commit 7a238fcba0
4 changed files with 40 additions and 16 deletions
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30
include/linux/nsproxy.h
View file

@ -35,22 +35,30 @@ struct nsproxy *dup_namespaces(struct nsproxy *orig);
int copy_namespaces(int flags, struct task_struct *tsk);
void get_task_namespaces(struct task_struct *tsk);
void free_nsproxy(struct nsproxy *ns);
struct nsproxy *put_nsproxy(struct nsproxy *ns);
static inline void put_nsproxy(struct nsproxy *ns)
static inline void finalize_put_nsproxy(struct nsproxy *ns)
{
if (atomic_dec_and_test(&ns->count)) {
if (ns)
free_nsproxy(ns);
}
}
static inline void exit_task_namespaces(struct task_struct *p)
static inline void put_and_finalize_nsproxy(struct nsproxy *ns)
{
struct nsproxy *ns = p->nsproxy;
if (ns) {
task_lock(p);
p->nsproxy = NULL;
task_unlock(p);
put_nsproxy(ns);
}
finalize_put_nsproxy(put_nsproxy(ns));
}
static inline struct nsproxy *preexit_task_namespaces(struct task_struct *p)
{
return put_nsproxy(p->nsproxy);
}
static inline void exit_task_namespaces(struct task_struct *p,
struct nsproxy *ns)
{
task_lock(p);
p->nsproxy = NULL;
task_unlock(p);
finalize_put_nsproxy(ns);
}
#endif

6
kernel/exit.c
View file

@ -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;

4
kernel/fork.c
View file

@ -1265,7 +1265,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
return p;
bad_fork_cleanup_namespaces:
exit_task_namespaces(p);
put_and_finalize_nsproxy(p->nsproxy);
bad_fork_cleanup_keys:
exit_keys(p);
bad_fork_cleanup_mm:
@ -1711,7 +1711,7 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
}
if (new_nsproxy)
put_nsproxy(new_nsproxy);
put_and_finalize_nsproxy(new_nsproxy);
bad_unshare_cleanup_ipc:
if (new_ipc)

16
kernel/nsproxy.c
View file

@ -117,7 +117,7 @@ int copy_namespaces(int flags, struct task_struct *tsk)
goto out_pid;
out:
put_nsproxy(old_ns);
put_and_finalize_nsproxy(old_ns);
return err;
out_pid:
@ -135,6 +135,20 @@ out_ns:
goto out;
}
struct nsproxy *put_nsproxy(struct nsproxy *ns)
{
if (ns) {
if (atomic_dec_and_test(&ns->count)) {
if (ns->mnt_ns) {
put_mnt_ns(ns->mnt_ns);
ns->mnt_ns = NULL;
}
return ns;
}
}
return NULL;
}
void free_nsproxy(struct nsproxy *ns)
{
if (ns->mnt_ns)