The only reply that I got to my last patchset to fix the use-after-free
problem in lockd was from Christoph Hellwig, who said:
> might be better to do the refcounting outside the thread and use the
> kthread api, which is something we still need to do for lockd anyway.
This patchset is an attempt to implement that suggestion. The first
two patches add a new svc_create_kthread() function that works like
svc_create_thread, but uses the kthread API under the covers. The rest
of the patches convert lockd to use this function (and fix a couple of
lockd bugs). The final patch adds reference counting that's needed
to fix the original problem.
Unfortunately, moving the refcounting outside of the thread altogether
isn't feasible for reasons outlined in description of the 6th patch.
Comments and suggestions appreciated...
Signed-off-by: Jeff Layton <[email protected]>
lockd makes itself freezable, but never calls try_to_freeze(). Have it
call try_to_freeze() within the main loop.
Signed-off-by: Jeff Layton <[email protected]>
---
fs/lockd/svc.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)
diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index 0f4148a..03a83a0 100644
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -155,6 +155,9 @@ lockd(struct svc_rqst *rqstp)
long timeout = MAX_SCHEDULE_TIMEOUT;
char buf[RPC_MAX_ADDRBUFLEN];
+ if (try_to_freeze())
+ continue;
+
if (signalled()) {
flush_signals(current);
if (nlmsvc_ops) {
--
1.5.3.3
Have lockd_up start lockd using svc_create_kthread. With this change,
lockd_down now blocks until lockd actually exits, so there's no longer
need for the waitqueue code at the end of lockd_down. This also means
that only one lockd can be running at a time which simplifies the code
within lockd's main loop a bit.
Signed-off-by: Jeff Layton <[email protected]>
---
fs/lockd/svc.c | 53 ++++++++++++++++-------------------------------------
1 files changed, 16 insertions(+), 37 deletions(-)
diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index 03a83a0..1303ce8 100644
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -25,6 +25,7 @@
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/mutex.h>
+#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/sunrpc/types.h>
@@ -48,13 +49,12 @@ EXPORT_SYMBOL(nlmsvc_ops);
static DEFINE_MUTEX(nlmsvc_mutex);
static unsigned int nlmsvc_users;
-static pid_t nlmsvc_pid;
-static struct svc_serv *nlmsvc_serv;
+static struct task_struct * nlmsvc_task;
+static struct svc_serv * nlmsvc_serv;
int nlmsvc_grace_period;
unsigned long nlmsvc_timeout;
static DECLARE_COMPLETION(lockd_start_done);
-static DECLARE_WAIT_QUEUE_HEAD(lockd_exit);
/*
* These can be set at insmod time (useful for NFS as root filesystem),
@@ -128,11 +128,10 @@ lockd(struct svc_rqst *rqstp)
/*
* Let our maker know we're running.
*/
- nlmsvc_pid = current->pid;
+ nlmsvc_task = current;
nlmsvc_serv = rqstp->rq_server;
complete(&lockd_start_done);
- daemonize("lockd");
set_freezable();
/* Process request with signals blocked, but allow SIGKILL. */
@@ -151,7 +150,7 @@ lockd(struct svc_rqst *rqstp)
* NFS mount or NFS daemon has gone away, and we've been sent a
* signal, or else another process has taken over our job.
*/
- while ((nlmsvc_users || !signalled()) && nlmsvc_pid == current->pid) {
+ while (!kthread_should_stop()) {
long timeout = MAX_SCHEDULE_TIMEOUT;
char buf[RPC_MAX_ADDRBUFLEN];
@@ -203,23 +202,18 @@ lockd(struct svc_rqst *rqstp)
* Check whether there's a new lockd process before
* shutting down the hosts and clearing the slot.
*/
- if (!nlmsvc_pid || current->pid == nlmsvc_pid) {
- if (nlmsvc_ops)
- nlmsvc_invalidate_all();
- nlm_shutdown_hosts();
- nlmsvc_pid = 0;
- nlmsvc_serv = NULL;
- } else
- printk(KERN_DEBUG
- "lockd: new process, skipping host shutdown\n");
- wake_up(&lockd_exit);
+ if (nlmsvc_ops)
+ nlmsvc_invalidate_all();
+ nlm_shutdown_hosts();
+ nlmsvc_task = NULL;
+ nlmsvc_serv = NULL;
/* Exit the RPC thread */
svc_exit_thread(rqstp);
/* Release module */
unlock_kernel();
- module_put_and_exit(0);
+ module_put(THIS_MODULE);
}
@@ -276,7 +270,7 @@ lockd_up(int proto) /* Maybe add a 'family' option when IPv6 is supported ?? */
/*
* Check whether we're already up and running.
*/
- if (nlmsvc_pid) {
+ if (nlmsvc_task) {
if (proto)
error = make_socks(nlmsvc_serv, proto);
goto out;
@@ -304,7 +298,7 @@ lockd_up(int proto) /* Maybe add a 'family' option when IPv6 is supported ?? */
* Create the kernel thread and wait for it to start.
*/
init_completion(&lockd_start_done);
- error = svc_create_thread(lockd, serv);
+ error = svc_create_kthread(lockd, serv, &serv->sv_pools[0]);
if (error) {
printk(KERN_WARNING
"lockd_up: create thread failed, error=%d\n", error);
@@ -339,30 +333,15 @@ lockd_down(void)
if (--nlmsvc_users)
goto out;
} else
- printk(KERN_WARNING "lockd_down: no users! pid=%d\n", nlmsvc_pid);
+ printk(KERN_WARNING "lockd_down: no users! task=%p\n", nlmsvc_task);
- if (!nlmsvc_pid) {
+ if (!nlmsvc_task) {
if (warned++ == 0)
printk(KERN_WARNING "lockd_down: no lockd running.\n");
goto out;
}
warned = 0;
-
- kill_proc(nlmsvc_pid, SIGKILL, 1);
- /*
- * Wait for the lockd process to exit, but since we're holding
- * the lockd semaphore, we can't wait around forever ...
- */
- clear_thread_flag(TIF_SIGPENDING);
- interruptible_sleep_on_timeout(&lockd_exit, HZ);
- if (nlmsvc_pid) {
- printk(KERN_WARNING
- "lockd_down: lockd failed to exit, clearing pid\n");
- nlmsvc_pid = 0;
- }
- spin_lock_irq(¤t->sighand->siglock);
- recalc_sigpending();
- spin_unlock_irq(¤t->sighand->siglock);
+ kthread_stop(nlmsvc_task);
out:
mutex_unlock(&nlmsvc_mutex);
}
--
1.5.3.3
...and only have lockd exit when the last reference is dropped. This
means that we can't use kthread_stop here. nlmsvc_unlink_block is called
by lockd and a kthread can't call kthread_stop on itself. So, change
lockd to check the refcount itself and to return if it goes to 0. We do
the checking and exit while holding the nlmsvc_mutex to make sure that a
new lockd is not started until the old one is down.
Signed-off-by: Jeff Layton <[email protected]>
---
fs/lockd/svc.c | 51 ++++++++++++++++++++++++++++++++----------
fs/lockd/svclock.c | 5 ++++
include/linux/lockd/lockd.h | 1 +
3 files changed, 45 insertions(+), 12 deletions(-)
diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index 1303ce8..05d2317 100644
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -51,6 +51,7 @@ static DEFINE_MUTEX(nlmsvc_mutex);
static unsigned int nlmsvc_users;
static struct task_struct * nlmsvc_task;
static struct svc_serv * nlmsvc_serv;
+atomic_t nlmsvc_ref = ATOMIC_INIT(0);
int nlmsvc_grace_period;
unsigned long nlmsvc_timeout;
@@ -134,7 +135,10 @@ lockd(struct svc_rqst *rqstp)
set_freezable();
- /* Process request with signals blocked, but allow SIGKILL. */
+ /*
+ * Process request with signals blocked, but allow SIGKILL which
+ * signifies that lockd should drop all of its locks.
+ */
allow_signal(SIGKILL);
dprintk("NFS locking service started (ver " LOCKD_VERSION ").\n");
@@ -147,15 +151,19 @@ lockd(struct svc_rqst *rqstp)
/*
* The main request loop. We don't terminate until the last
- * NFS mount or NFS daemon has gone away, and we've been sent a
- * signal, or else another process has taken over our job.
+ * NFS mount or NFS daemon has gone away, and the nlm_blocked
+ * list is empty. The nlmsvc_mutex ensures that we prevent a
+ * new lockd from being started before the old one is down.
*/
- while (!kthread_should_stop()) {
+ mutex_lock(&nlmsvc_mutex);
+ while (atomic_read(&nlmsvc_ref) != 0) {
long timeout = MAX_SCHEDULE_TIMEOUT;
char buf[RPC_MAX_ADDRBUFLEN];
+ mutex_unlock(&nlmsvc_mutex);
+
if (try_to_freeze())
- continue;
+ goto again;
if (signalled()) {
flush_signals(current);
@@ -182,11 +190,12 @@ lockd(struct svc_rqst *rqstp)
*/
err = svc_recv(rqstp, timeout);
if (err == -EAGAIN || err == -EINTR)
- continue;
+ goto again;
if (err < 0) {
printk(KERN_WARNING
"lockd: terminating on error %d\n",
-err);
+ mutex_lock(&nlmsvc_mutex);
break;
}
@@ -194,19 +203,22 @@ lockd(struct svc_rqst *rqstp)
svc_print_addr(rqstp, buf, sizeof(buf)));
svc_process(rqstp);
+again:
+ mutex_lock(&nlmsvc_mutex);
}
- flush_signals(current);
-
/*
- * Check whether there's a new lockd process before
- * shutting down the hosts and clearing the slot.
- */
+ * at this point lockd is committed to going down. We hold the
+ * nlmsvc_mutex until just before exit to prevent a new one
+ * from starting before it's down.
+ */
+ flush_signals(current);
if (nlmsvc_ops)
nlmsvc_invalidate_all();
nlm_shutdown_hosts();
nlmsvc_task = NULL;
nlmsvc_serv = NULL;
+ mutex_unlock(&nlmsvc_mutex);
/* Exit the RPC thread */
svc_exit_thread(rqstp);
@@ -267,6 +279,10 @@ lockd_up(int proto) /* Maybe add a 'family' option when IPv6 is supported ?? */
int error = 0;
mutex_lock(&nlmsvc_mutex);
+
+ if (!nlmsvc_users)
+ atomic_inc(&nlmsvc_ref);
+
/*
* Check whether we're already up and running.
*/
@@ -313,6 +329,8 @@ lockd_up(int proto) /* Maybe add a 'family' option when IPv6 is supported ?? */
destroy_and_out:
svc_destroy(serv);
out:
+ if (!nlmsvc_users && error)
+ atomic_dec(&nlmsvc_ref);
if (!error)
nlmsvc_users++;
mutex_unlock(&nlmsvc_mutex);
@@ -341,7 +359,16 @@ lockd_down(void)
goto out;
}
warned = 0;
- kthread_stop(nlmsvc_task);
+ atomic_dec(&nlmsvc_ref);
+
+ /*
+ * Sending a signal is necessary here. If we get to this point and
+ * nlm_blocked isn't empty then lockd may be held hostage by clients
+ * that are still blocking. Sending the signal makes sure that lockd
+ * invalidates all of its locks so that it's just waiting on RPC
+ * callbacks to complete
+ */
+ kill_proc(nlmsvc_task->pid, SIGKILL, 1);
out:
mutex_unlock(&nlmsvc_mutex);
}
diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index d120ec3..b8fbda3 100644
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -61,6 +61,9 @@ nlmsvc_insert_block(struct nlm_block *block, unsigned long when)
struct list_head *pos;
dprintk("lockd: nlmsvc_insert_block(%p, %ld)\n", block, when);
+ if (list_empty(&nlm_blocked))
+ atomic_inc(&nlmsvc_ref);
+
if (list_empty(&block->b_list)) {
kref_get(&block->b_count);
} else {
@@ -239,6 +242,8 @@ static int nlmsvc_unlink_block(struct nlm_block *block)
/* Remove block from list */
status = posix_unblock_lock(block->b_file->f_file, &block->b_call->a_args.lock.fl);
nlmsvc_remove_block(block);
+ if (list_empty(&nlm_blocked))
+ atomic_dec(&nlmsvc_ref);
return status;
}
diff --git a/include/linux/lockd/lockd.h b/include/linux/lockd/lockd.h
index e2d1ce3..7389553 100644
--- a/include/linux/lockd/lockd.h
+++ b/include/linux/lockd/lockd.h
@@ -154,6 +154,7 @@ extern struct svc_procedure nlmsvc_procedures4[];
extern int nlmsvc_grace_period;
extern unsigned long nlmsvc_timeout;
extern int nsm_use_hostnames;
+extern atomic_t nlmsvc_ref;
/*
* Lockd client functions
--
1.5.3.3
On Thu, Dec 13, 2007 at 03:40:24PM -0500, Jeff Layton wrote:
> Move the initialization that happens prior to thread creation to a new
> function (svc_prepare_thread) so that we can call it from a new thread
> creation routine. Add a new function svc_create_kthread that spawns svc
> threads using kthread API.
>
> We should be able to eventually convert all of the callers to the
> kthread API, at which point we can drop __svc_create_thread.
> +static struct svc_rqst *
> +svc_prepare_thread(svc_thread_fn func, struct svc_serv *serv,
> + struct svc_pool *pool)
Could you just export this helper? I'd rather have callers have full
control over how they create their threads and call into a helper to
initialize the sunrpc state.
On Thu, 13 Dec 2007 21:06:44 +0000
Christoph Hellwig <[email protected]> wrote:
> On Thu, Dec 13, 2007 at 03:40:24PM -0500, Jeff Layton wrote:
> > Move the initialization that happens prior to thread creation to a
> > new function (svc_prepare_thread) so that we can call it from a new
> > thread creation routine. Add a new function svc_create_kthread that
> > spawns svc threads using kthread API.
> >
> > We should be able to eventually convert all of the callers to the
> > kthread API, at which point we can drop __svc_create_thread.
>
> > +static struct svc_rqst *
> > +svc_prepare_thread(svc_thread_fn func, struct svc_serv *serv,
> > + struct svc_pool *pool)
>
> Could you just export this helper? I'd rather have callers have full
> control over how they create their threads and call into a helper to
> initialize the sunrpc state.
>
Sure, sounds reasonable. Once I collect comments on this patch and do a
respin, I'll plan to export that symbol.
Thanks,
--
Jeff Layton <[email protected]>
lockd_start_done is a global var that can be reused if lockd is
restarted, but it's never reinitialized. On all but the first use,
wait_for_completion isn't actually waiting on it since it has
already completed once.
Signed-off-by: Jeff Layton <[email protected]>
---
fs/lockd/svc.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)
diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index 82e2192..0f4148a 100644
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -300,6 +300,7 @@ lockd_up(int proto) /* Maybe add a 'family' option when IPv6 is supported ?? */
/*
* Create the kernel thread and wait for it to start.
*/
+ init_completion(&lockd_start_done);
error = svc_create_thread(lockd, serv);
if (error) {
printk(KERN_WARNING
--
1.5.3.3
svc_pool_map_set_cpumask will only affect "current" as of now. Add a
new arg so that it can change the cpumask on any given task. Also if
we're not changing "current" we don't care what the oldmask was, so
allow it to be a NULL pointer.
Signed-off-by: Jeff Layton <[email protected]>
---
net/sunrpc/svc.c | 16 ++++++++++------
1 files changed, 10 insertions(+), 6 deletions(-)
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index a4a6bf7..9696ae7 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -297,7 +297,8 @@ svc_pool_map_put(void)
* Returns 1 and fills in oldmask iff a cpumask was applied.
*/
static inline int
-svc_pool_map_set_cpumask(unsigned int pidx, cpumask_t *oldmask)
+svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx,
+ cpumask_t *oldmask)
{
struct svc_pool_map *m = &svc_pool_map;
unsigned int node; /* or cpu */
@@ -314,13 +315,15 @@ svc_pool_map_set_cpumask(unsigned int pidx, cpumask_t *oldmask)
return 0;
case SVC_POOL_PERCPU:
node = m->pool_to[pidx];
- *oldmask = current->cpus_allowed;
- set_cpus_allowed(current, cpumask_of_cpu(node));
+ if (oldmask != NULL)
+ *oldmask = task->cpus_allowed;
+ set_cpus_allowed(task, cpumask_of_cpu(node));
return 1;
case SVC_POOL_PERNODE:
node = m->pool_to[pidx];
- *oldmask = current->cpus_allowed;
- set_cpus_allowed(current, node_to_cpumask(node));
+ if (oldmask != NULL)
+ *oldmask = task->cpus_allowed;
+ set_cpus_allowed(task, node_to_cpumask(node));
return 1;
}
}
@@ -569,7 +572,8 @@ __svc_create_thread(svc_thread_fn func, struct svc_serv *serv,
rqstp->rq_pool = pool;
if (serv->sv_nrpools > 1)
- have_oldmask = svc_pool_map_set_cpumask(pool->sp_id, &oldmask);
+ have_oldmask = svc_pool_map_set_cpumask(current, pool->sp_id,
+ &oldmask);
error = kernel_thread((int (*)(void *)) func, rqstp, 0);
--
1.5.3.3
Move the initialization that happens prior to thread creation to a new
function (svc_prepare_thread) so that we can call it from a new thread
creation routine. Add a new function svc_create_kthread that spawns svc
threads using kthread API.
We should be able to eventually convert all of the callers to the
kthread API, at which point we can drop __svc_create_thread.
Signed-off-by: Jeff Layton <[email protected]>
---
include/linux/sunrpc/svc.h | 2 +
net/sunrpc/sunrpc_syms.c | 1 +
net/sunrpc/svc.c | 69 +++++++++++++++++++++++++++++++++++++++----
3 files changed, 65 insertions(+), 7 deletions(-)
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 8531a70..fd980af 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -383,6 +383,8 @@ struct svc_procedure {
struct svc_serv * svc_create(struct svc_program *, unsigned int,
void (*shutdown)(struct svc_serv*));
int svc_create_thread(svc_thread_fn, struct svc_serv *);
+int svc_create_kthread(svc_thread_fn func,
+ struct svc_serv *serv, struct svc_pool *pool);
void svc_exit_thread(struct svc_rqst *);
struct svc_serv * svc_create_pooled(struct svc_program *, unsigned int,
void (*shutdown)(struct svc_serv*),
diff --git a/net/sunrpc/sunrpc_syms.c b/net/sunrpc/sunrpc_syms.c
index 33d89e8..7feb878 100644
--- a/net/sunrpc/sunrpc_syms.c
+++ b/net/sunrpc/sunrpc_syms.c
@@ -64,6 +64,7 @@ EXPORT_SYMBOL(put_rpccred);
/* RPC server stuff */
EXPORT_SYMBOL(svc_create);
EXPORT_SYMBOL(svc_create_thread);
+EXPORT_SYMBOL(svc_create_kthread);
EXPORT_SYMBOL(svc_create_pooled);
EXPORT_SYMBOL(svc_set_num_threads);
EXPORT_SYMBOL(svc_exit_thread);
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 9696ae7..d9c26e3 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -18,6 +18,7 @@
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/module.h>
+#include <linux/kthread.h>
#include <linux/sunrpc/types.h>
#include <linux/sunrpc/xdr.h>
@@ -543,18 +544,15 @@ svc_release_buffer(struct svc_rqst *rqstp)
* On a NUMA or SMP machine, with a multi-pool serv, the thread
* will be restricted to run on the cpus belonging to the pool.
*/
-static int
-__svc_create_thread(svc_thread_fn func, struct svc_serv *serv,
- struct svc_pool *pool)
+static struct svc_rqst *
+svc_prepare_thread(svc_thread_fn func, struct svc_serv *serv,
+ struct svc_pool *pool)
{
struct svc_rqst *rqstp;
- int error = -ENOMEM;
- int have_oldmask = 0;
- cpumask_t oldmask;
rqstp = kzalloc(sizeof(*rqstp), GFP_KERNEL);
if (!rqstp)
- goto out;
+ goto out_enomem;
init_waitqueue_head(&rqstp->rq_wait);
@@ -570,6 +568,30 @@ __svc_create_thread(svc_thread_fn func, struct svc_serv *serv,
spin_unlock_bh(&pool->sp_lock);
rqstp->rq_server = serv;
rqstp->rq_pool = pool;
+out:
+ return rqstp;
+
+out_thread:
+ svc_exit_thread(rqstp);
+out_enomem:
+ rqstp = ERR_PTR(-ENOMEM);
+ goto out;
+}
+
+static int
+__svc_create_thread(svc_thread_fn func, struct svc_serv *serv,
+ struct svc_pool *pool)
+{
+ struct svc_rqst *rqstp;
+ int have_oldmask = 0;
+ cpumask_t oldmask;
+ int error;
+
+ rqstp = svc_prepare_thread(func, serv, pool);
+ if (IS_ERR(rqstp)) {
+ error = PTR_ERR(rqstp);
+ goto out;
+ }
if (serv->sv_nrpools > 1)
have_oldmask = svc_pool_map_set_cpumask(current, pool->sp_id,
@@ -601,6 +623,39 @@ svc_create_thread(svc_thread_fn func, struct svc_serv *serv)
return __svc_create_thread(func, serv, &serv->sv_pools[0]);
}
+int
+svc_create_kthread(svc_thread_fn func, struct svc_serv *serv,
+ struct svc_pool *pool)
+{
+ struct svc_rqst *rqstp;
+ struct task_struct *task;
+ int error = 0;
+
+ rqstp = svc_prepare_thread(func, serv, pool);
+ if (IS_ERR(rqstp)) {
+ error = PTR_ERR(rqstp);
+ goto out;
+ }
+
+ task = kthread_create((int (*)(void *)) func, rqstp, serv->sv_name);
+ if (IS_ERR(task)) {
+ error = PTR_ERR(task);
+ goto out_thread;
+ }
+
+ if (serv->sv_nrpools > 1)
+ svc_pool_map_set_cpumask(task, pool->sp_id, NULL);
+
+ svc_sock_update_bufs(serv);
+ wake_up_process(task);
+out:
+ return error;
+
+out_thread:
+ svc_exit_thread(rqstp);
+ goto out;
+}
+
/*
* Choose a pool in which to create a new thread, for svc_set_num_threads
*/
--
1.5.3.3