This is a note to let you know that I've just added the patch titled
target: close target_put_sess_cmd() vs. core_tmr_abort_task() race
to the 3.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
target-close-target_put_sess_cmd-vs.-core_tmr_abort_task-race.patch
and it can be found in the queue-3.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From ccf5ae83a6cf3d9cfe9a7038bfe7cd38ab03d5e1 Mon Sep 17 00:00:00 2001
From: Joern Engel <joern@xxxxxxxxx>
Date: Mon, 13 May 2013 16:30:06 -0400
Subject: target: close target_put_sess_cmd() vs. core_tmr_abort_task() race
From: Joern Engel <joern@xxxxxxxxx>
commit ccf5ae83a6cf3d9cfe9a7038bfe7cd38ab03d5e1 upstream.
It is possible for one thread to to take se_sess->sess_cmd_lock in
core_tmr_abort_task() before taking a reference count on
se_cmd->cmd_kref, while another thread in target_put_sess_cmd() drops
se_cmd->cmd_kref before taking se_sess->sess_cmd_lock.
This introduces kref_put_spinlock_irqsave() and uses it in
target_put_sess_cmd() to close the race window.
Signed-off-by: Joern Engel <joern@xxxxxxxxx>
Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/target/target_core_transport.c | 11 +++++------
include/linux/kref.h | 33 +++++++++++++++++++++++++++++++++
2 files changed, 38 insertions(+), 6 deletions(-)
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -2213,21 +2213,19 @@ static void target_release_cmd_kref(stru
{
struct se_cmd *se_cmd = container_of(kref, struct se_cmd, cmd_kref);
struct se_session *se_sess = se_cmd->se_sess;
- unsigned long flags;
- spin_lock_irqsave(&se_sess->sess_cmd_lock, flags);
if (list_empty(&se_cmd->se_cmd_list)) {
- spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
+ spin_unlock(&se_sess->sess_cmd_lock);
se_cmd->se_tfo->release_cmd(se_cmd);
return;
}
if (se_sess->sess_tearing_down && se_cmd->cmd_wait_set) {
- spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
+ spin_unlock(&se_sess->sess_cmd_lock);
complete(&se_cmd->cmd_wait_comp);
return;
}
list_del(&se_cmd->se_cmd_list);
- spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
+ spin_unlock(&se_sess->sess_cmd_lock);
se_cmd->se_tfo->release_cmd(se_cmd);
}
@@ -2238,7 +2236,8 @@ static void target_release_cmd_kref(stru
*/
int target_put_sess_cmd(struct se_session *se_sess, struct se_cmd *se_cmd)
{
- return kref_put(&se_cmd->cmd_kref, target_release_cmd_kref);
+ return kref_put_spinlock_irqsave(&se_cmd->cmd_kref, target_release_cmd_kref,
+ &se_sess->sess_cmd_lock);
}
EXPORT_SYMBOL(target_put_sess_cmd);
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -19,6 +19,7 @@
#include <linux/atomic.h>
#include <linux/kernel.h>
#include <linux/mutex.h>
+#include <linux/spinlock.h>
struct kref {
atomic_t refcount;
@@ -95,6 +96,38 @@ static inline int kref_put(struct kref *
return kref_sub(kref, 1, release);
}
+/**
+ * kref_put_spinlock_irqsave - decrement refcount for object.
+ * @kref: object.
+ * @release: pointer to the function that will clean up the object when the
+ * last reference to the object is released.
+ * This pointer is required, and it is not acceptable to pass kfree
+ * in as this function.
+ * @lock: lock to take in release case
+ *
+ * Behaves identical to kref_put with one exception. If the reference count
+ * drops to zero, the lock will be taken atomically wrt dropping the reference
+ * count. The release function has to call spin_unlock() without _irqrestore.
+ */
+static inline int kref_put_spinlock_irqsave(struct kref *kref,
+ void (*release)(struct kref *kref),
+ spinlock_t *lock)
+{
+ unsigned long flags;
+
+ WARN_ON(release == NULL);
+ if (atomic_add_unless(&kref->refcount, -1, 1))
+ return 0;
+ spin_lock_irqsave(lock, flags);
+ if (atomic_dec_and_test(&kref->refcount)) {
+ release(kref);
+ local_irq_restore(flags);
+ return 1;
+ }
+ spin_unlock_irqrestore(lock, flags);
+ return 0;
+}
+
static inline int kref_put_mutex(struct kref *kref,
void (*release)(struct kref *kref),
struct mutex *lock)
Patches currently in stable-queue which might be from joern@xxxxxxxxx are
queue-3.9/target-close-target_put_sess_cmd-vs.-core_tmr_abort_task-race.patch
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