Re: [PATCH 2/3] target: close target_put_sess_cmd() vs.core_tmr_abort_task() race v5

[Nicholas A. Bellinger]

On Mon, 2013-05-13 at 16:30 -0400, Joern Engel wrote:
> 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>
> ---

I'm fine with applying this one..

Greg-KH, are you OK with the kref.h changes here..?

--nab

>  drivers/target/target_core_transport.c |   11 +++++------
>  include/linux/kref.h                   |   33 ++++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
> index 3243ea7..0d46276 100644
> --- a/drivers/target/target_core_transport.c
> +++ b/drivers/target/target_core_transport.c
> @@ -2213,21 +2213,19 @@ static void target_release_cmd_kref(struct kref *kref)
>  {
>  	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(struct kref *kref)
>   */
>  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);
>  
> diff --git a/include/linux/kref.h b/include/linux/kref.h
> index 4972e6e..7419c02 100644
> --- 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 *kref, void (*release)(struct kref *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)


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