Re: [PATCH -mm1 1/2] fixing idr_find() locking

[Jarek Poplawski]

On Thu, Sep 27, 2007 at 04:33:55PM +0200, Nadia.Derbey@xxxxxxxx wrote:
> [PATCH 01/02]
> 
> 
> This is a patch that fixes the way idr_find() used to be called in ipc_lock():
> in all the paths that don't imply an update of the ipcs idr, it was called
> without the idr tree being locked.
> 
> The changes are:
>   . in ipc_ids, the mutex has been changed into a reader/writer semaphore.
>   . ipc_lock() now takes the mutex as a reader during the idr_find().
>   . a new routine ipc_lock_down() has been defined: it doesn't take the
>     mutex, assuming that it is being held by the caller. This is the routine
>     that is now called in all the update paths.
> 
> 
> Signed-off-by: Nadia Derbey <Nadia.Derbey@xxxxxxxx>

Acked-by: Jarek Poplawski <jarkao2@xxxxx>

PS: there is one big mistake around To/Cc ordering, so I doubt Andrew
will ever sign this...

> 
> ---
> 
> This patch applies on top of the 2.6.23-rc6-mm1
> 
> 
>  ipc/msg.c  |   41 ++++++++++++++++++++++----------
>  ipc/sem.c  |   44 +++++++++++++++++++++++-----------
>  ipc/shm.c  |   77 +++++++++++++++++++++++++++++++++++++++---------------------
>  ipc/util.c |   78 ++++++++++++++++++++++++++++++++++++++++++++++++-------------
>  ipc/util.h |   28 ++++++++++++++++++++-
>  5 files changed, 198 insertions(+), 70 deletions(-)
> 
> Index: linux-2.6.23-rc6-mm1/ipc/util.h
> ===================================================================
> --- linux-2.6.23-rc6-mm1.orig/ipc/util.h	2007-09-25 12:38:17.000000000 +0200
> +++ linux-2.6.23-rc6-mm1/ipc/util.h	2007-09-27 10:13:18.000000000 +0200
> @@ -32,7 +32,7 @@ struct ipc_ids {
>  	int in_use;
>  	unsigned short seq;
>  	unsigned short seq_max;
> -	struct mutex mutex;
> +	struct rw_semaphore rw_mutex;
>  	struct idr ipcs_idr;
>  };
>  
> @@ -81,8 +81,10 @@ void __init ipc_init_proc_interface(cons
>  
>  #define ipcid_to_idx(id) ((id) % SEQ_MULTIPLIER)
>  
> -/* must be called with ids->mutex acquired.*/
> +/* must be called with ids->rw_mutex acquired for writing */
>  int ipc_addid(struct ipc_ids *, struct kern_ipc_perm *, int);
> +
> +/* must be called with ids->rw_mutex acquired for reading */
>  int ipc_get_maxid(struct ipc_ids *);
>  
>  /* must be called with both locks acquired. */
> @@ -107,6 +109,11 @@ void* ipc_rcu_alloc(int size);
>  void ipc_rcu_getref(void *ptr);
>  void ipc_rcu_putref(void *ptr);
>  
> +/*
> + * ipc_lock_down: called with rw_mutex held
> + * ipc_lock: called without that lock held
> + */
> +struct kern_ipc_perm *ipc_lock_down(struct ipc_ids *, int);
>  struct kern_ipc_perm *ipc_lock(struct ipc_ids *, int);
>  
>  void kernel_to_ipc64_perm(struct kern_ipc_perm *in, struct ipc64_perm *out);
> @@ -155,6 +162,23 @@ static inline void ipc_unlock(struct ker
>  	rcu_read_unlock();
>  }
>  
> +static inline struct kern_ipc_perm *ipc_lock_check_down(struct ipc_ids *ids,
> +						int id)
> +{
> +	struct kern_ipc_perm *out;
> +
> +	out = ipc_lock_down(ids, id);
> +	if (IS_ERR(out))
> +		return out;
> +
> +	if (ipc_checkid(ids, out, id)) {
> +		ipc_unlock(out);
> +		return ERR_PTR(-EIDRM);
> +	}
> +
> +	return out;
> +}
> +
>  static inline struct kern_ipc_perm *ipc_lock_check(struct ipc_ids *ids,
>  						int id)
>  {
> Index: linux-2.6.23-rc6-mm1/ipc/util.c
> ===================================================================
> --- linux-2.6.23-rc6-mm1.orig/ipc/util.c	2007-09-21 10:32:03.000000000 +0200
> +++ linux-2.6.23-rc6-mm1/ipc/util.c	2007-09-27 14:37:55.000000000 +0200
> @@ -32,6 +32,7 @@
>  #include <linux/proc_fs.h>
>  #include <linux/audit.h>
>  #include <linux/nsproxy.h>
> +#include <linux/rwsem.h>
>  
>  #include <asm/unistd.h>
>  
> @@ -136,7 +137,7 @@ __initcall(ipc_init);
>   
>  void ipc_init_ids(struct ipc_ids *ids)
>  {
> -	mutex_init(&ids->mutex);
> +	init_rwsem(&ids->rw_mutex);
>  
>  	ids->in_use = 0;
>  	ids->seq = 0;
> @@ -191,7 +192,7 @@ void __init ipc_init_proc_interface(cons
>   *	@ids: Identifier set
>   *	@key: The key to find
>   *	
> - *	Requires ipc_ids.mutex locked.
> + *	Requires ipc_ids.rw_mutex locked.
>   *	Returns the LOCKED pointer to the ipc structure if found or NULL
>   *	if not.
>   *	If key is found ipc points to the owning ipc structure
> @@ -225,7 +226,7 @@ static struct kern_ipc_perm *ipc_findkey
>   *	ipc_get_maxid 	-	get the last assigned id
>   *	@ids: IPC identifier set
>   *
> - *	Called with ipc_ids.mutex held.
> + *	Called with ipc_ids.rw_mutex held.
>   */
>  
>  int ipc_get_maxid(struct ipc_ids *ids)
> @@ -263,7 +264,7 @@ int ipc_get_maxid(struct ipc_ids *ids)
>   *	is returned. The 'new' entry is returned in a locked state on success.
>   *	On failure the entry is not locked and -1 is returned.
>   *
> - *	Called with ipc_ids.mutex held.
> + *	Called with ipc_ids.rw_mutex held as a writer.
>   */
>   
>  int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
> @@ -316,9 +317,9 @@ int ipcget_new(struct ipc_namespace *ns,
>  	if (!err)
>  		return -ENOMEM;
>  
> -	mutex_lock(&ids->mutex);
> +	down_write(&ids->rw_mutex);
>  	err = ops->getnew(ns, params);
> -	mutex_unlock(&ids->mutex);
> +	up_write(&ids->rw_mutex);
>  
>  	return err;
>  }
> @@ -335,7 +336,7 @@ int ipcget_new(struct ipc_namespace *ns,
>   *
>   *	On success, the IPC id is returned.
>   *
> - *	It is called with ipc_ids.mutex and ipcp->lock held.
> + *	It is called with ipc_ids.rw_mutex and ipcp->lock held.
>   */
>  static int ipc_check_perms(struct kern_ipc_perm *ipcp, struct ipc_ops *ops,
>  			struct ipc_params *params)
> @@ -376,7 +377,11 @@ int ipcget_public(struct ipc_namespace *
>  
>  	err = idr_pre_get(&ids->ipcs_idr, GFP_KERNEL);
>  
> -	mutex_lock(&ids->mutex);
> +	/*
> +	 * Take the lock as a writer since we are potentially going to add
> +	 * a new entry + read locks are not "upgradable"
> +	 */
> +	down_write(&ids->rw_mutex);
>  	ipcp = ipc_findkey(ids, params->key);
>  	if (ipcp == NULL) {
>  		/* key not used */
> @@ -404,7 +409,7 @@ int ipcget_public(struct ipc_namespace *
>  		}
>  		ipc_unlock(ipcp);
>  	}
> -	mutex_unlock(&ids->mutex);
> +	up_write(&ids->rw_mutex);
>  
>  	return err;
>  }
> @@ -415,8 +420,8 @@ int ipcget_public(struct ipc_namespace *
>   *	@ids: IPC identifier set
>   *	@ipcp: ipc perm structure containing the identifier to remove
>   *
> - *	ipc_ids.mutex and the spinlock for this ID are held before this
> - *	function is called, and remain locked on the exit.
> + *	ipc_ids.rw_mutex (as a writer) and the spinlock for this ID are held
> + *	before this function is called, and remain locked on the exit.
>   */
>   
>  void ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)
> @@ -680,15 +685,17 @@ void ipc64_perm_to_ipc_perm (struct ipc6
>  }
>  
>  /**
> - * ipc_lock - Lock an ipc structure
> + * ipc_lock - Lock an ipc structure without rw_mutex held
>   * @ids: IPC identifier set
>   * @id: ipc id to look for
>   *
>   * Look for an id in the ipc ids idr and lock the associated ipc object.
>   *
> - * ipc_ids.mutex is not necessarily held before this function is called,
> - * that's why we enter a RCU read section.
>   * The ipc object is locked on exit.
> + *
> + * This is the routine that should be called when the rw_mutex is not already
> + * held, i.e. idr tree not protected: it protects the idr tree in read mode
> + * during the idr_find().
>   */
>  
>  struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
> @@ -696,13 +703,18 @@ struct kern_ipc_perm *ipc_lock(struct ip
>  	struct kern_ipc_perm *out;
>  	int lid = ipcid_to_idx(id);
>  
> +	down_read(&ids->rw_mutex);
> +
>  	rcu_read_lock();
>  	out = idr_find(&ids->ipcs_idr, lid);
>  	if (out == NULL) {
>  		rcu_read_unlock();
> +		up_read(&ids->rw_mutex);
>  		return ERR_PTR(-EINVAL);
>  	}
>  
> +	up_read(&ids->rw_mutex);
> +
>  	spin_lock(&out->lock);
>  	
>  	/* ipc_rmid() may have already freed the ID while ipc_lock
> @@ -717,6 +729,40 @@ struct kern_ipc_perm *ipc_lock(struct ip
>  	return out;
>  }
>  
> +/**
> + * ipc_lock_down - Lock an ipc structure with rw_sem held
> + * @ids: IPC identifier set
> + * @id: ipc id to look for
> + *
> + * Look for an id in the ipc ids idr and lock the associated ipc object.
> + *
> + * The ipc object is locked on exit.
> + *
> + * This is the routine that should be called when the rw_mutex is already
> + * held, i.e. idr tree protected.
> + */
> +
> +struct kern_ipc_perm *ipc_lock_down(struct ipc_ids *ids, int id)
> +{
> +	struct kern_ipc_perm *out;
> +	int lid = ipcid_to_idx(id);
> +
> +	rcu_read_lock();
> +	out = idr_find(&ids->ipcs_idr, lid);
> +	if (out == NULL) {
> +		rcu_read_unlock();
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	spin_lock(&out->lock);
> +
> +	/*
> +	 * No need to verify that the structure is still valid since the
> +	 * rw_mutex is held.
> +	 */
> +	return out;
> +}
> +
>  #ifdef __ARCH_WANT_IPC_PARSE_VERSION
>  
>  
> @@ -808,7 +854,7 @@ static void *sysvipc_proc_start(struct s
>  	 * Take the lock - this will be released by the corresponding
>  	 * call to stop().
>  	 */
> -	mutex_lock(&ids->mutex);
> +	down_read(&ids->rw_mutex);
>  
>  	/* pos < 0 is invalid */
>  	if (*pos < 0)
> @@ -835,7 +881,7 @@ static void sysvipc_proc_stop(struct seq
>  
>  	ids = iter->ns->ids[iface->ids];
>  	/* Release the lock we took in start() */
> -	mutex_unlock(&ids->mutex);
> +	up_read(&ids->rw_mutex);
>  }
>  
>  static int sysvipc_proc_show(struct seq_file *s, void *it)
> Index: linux-2.6.23-rc6-mm1/ipc/msg.c
> ===================================================================
> --- linux-2.6.23-rc6-mm1.orig/ipc/msg.c	2007-09-21 10:33:08.000000000 +0200
> +++ linux-2.6.23-rc6-mm1/ipc/msg.c	2007-09-27 10:34:25.000000000 +0200
> @@ -34,7 +34,7 @@
>  #include <linux/syscalls.h>
>  #include <linux/audit.h>
>  #include <linux/seq_file.h>
> -#include <linux/mutex.h>
> +#include <linux/rwsem.h>
>  #include <linux/nsproxy.h>
>  
>  #include <asm/current.h>
> @@ -110,7 +110,7 @@ void msg_exit_ns(struct ipc_namespace *n
>  	int next_id;
>  	int total, in_use;
>  
> -	mutex_lock(&msg_ids(ns).mutex);
> +	down_write(&msg_ids(ns).rw_mutex);
>  
>  	in_use = msg_ids(ns).in_use;
>  
> @@ -122,7 +122,8 @@ void msg_exit_ns(struct ipc_namespace *n
>  		freeque(ns, msq);
>  		total++;
>  	}
> -	mutex_unlock(&msg_ids(ns).mutex);
> +
> +	up_write(&msg_ids(ns).rw_mutex);
>  
>  	kfree(ns->ids[IPC_MSG_IDS]);
>  	ns->ids[IPC_MSG_IDS] = NULL;
> @@ -136,6 +137,22 @@ void __init msg_init(void)
>  				IPC_MSG_IDS, sysvipc_msg_proc_show);
>  }
>  
> +/*
> + * This routine is called in the paths where the rw_mutex is held to protect
> + * access to the idr tree.
> + */
> +static inline struct msg_queue *msg_lock_check_down(struct ipc_namespace *ns,
> +						int id)
> +{
> +	struct kern_ipc_perm *ipcp = ipc_lock_check_down(&msg_ids(ns), id);
> +
> +	return container_of(ipcp, struct msg_queue, q_perm);
> +}
> +
> +/*
> + * msg_lock_(check_) routines are called in the paths where the rw_mutex
> + * is not held.
> + */
>  static inline struct msg_queue *msg_lock(struct ipc_namespace *ns, int id)
>  {
>  	struct kern_ipc_perm *ipcp = ipc_lock(&msg_ids(ns), id);
> @@ -161,7 +178,7 @@ static inline void msg_rmid(struct ipc_n
>   * @ns: namespace
>   * @params: ptr to the structure that contains the key and msgflg
>   *
> - * Called with msg_ids.mutex held
> + * Called with msg_ids.rw_mutex held (writer)
>   */
>  static int newque(struct ipc_namespace *ns, struct ipc_params *params)
>  {
> @@ -260,8 +277,8 @@ static void expunge_all(struct msg_queue
>   * removes the message queue from message queue ID IDR, and cleans up all the
>   * messages associated with this queue.
>   *
> - * msg_ids.mutex and the spinlock for this message queue are held
> - * before freeque() is called. msg_ids.mutex remains locked on exit.
> + * msg_ids.rw_mutex (writer) and the spinlock for this message queue are held
> + * before freeque() is called. msg_ids.rw_mutex remains locked on exit.
>   */
>  static void freeque(struct ipc_namespace *ns, struct msg_queue *msq)
>  {
> @@ -286,7 +303,7 @@ static void freeque(struct ipc_namespace
>  }
>  
>  /*
> - * Called with msg_ids.mutex and ipcp locked.
> + * Called with msg_ids.rw_mutex and ipcp locked.
>   */
>  static inline int msg_security(struct kern_ipc_perm *ipcp, int msgflg)
>  {
> @@ -444,7 +461,7 @@ asmlinkage long sys_msgctl(int msqid, in
>  		msginfo.msgmnb = ns->msg_ctlmnb;
>  		msginfo.msgssz = MSGSSZ;
>  		msginfo.msgseg = MSGSEG;
> -		mutex_lock(&msg_ids(ns).mutex);
> +		down_read(&msg_ids(ns).rw_mutex);
>  		if (cmd == MSG_INFO) {
>  			msginfo.msgpool = msg_ids(ns).in_use;
>  			msginfo.msgmap = atomic_read(&msg_hdrs);
> @@ -455,7 +472,7 @@ asmlinkage long sys_msgctl(int msqid, in
>  			msginfo.msgtql = MSGTQL;
>  		}
>  		max_id = ipc_get_maxid(&msg_ids(ns));
> -		mutex_unlock(&msg_ids(ns).mutex);
> +		up_read(&msg_ids(ns).rw_mutex);
>  		if (copy_to_user(buf, &msginfo, sizeof(struct msginfo)))
>  			return -EFAULT;
>  		return (max_id < 0) ? 0 : max_id;
> @@ -516,8 +533,8 @@ asmlinkage long sys_msgctl(int msqid, in
>  		return  -EINVAL;
>  	}
>  
> -	mutex_lock(&msg_ids(ns).mutex);
> -	msq = msg_lock_check(ns, msqid);
> +	down_write(&msg_ids(ns).rw_mutex);
> +	msq = msg_lock_check_down(ns, msqid);
>  	if (IS_ERR(msq)) {
>  		err = PTR_ERR(msq);
>  		goto out_up;
> @@ -576,7 +593,7 @@ asmlinkage long sys_msgctl(int msqid, in
>  	}
>  	err = 0;
>  out_up:
> -	mutex_unlock(&msg_ids(ns).mutex);
> +	up_write(&msg_ids(ns).rw_mutex);
>  	return err;
>  out_unlock_up:
>  	msg_unlock(msq);
> Index: linux-2.6.23-rc6-mm1/ipc/sem.c
> ===================================================================
> --- linux-2.6.23-rc6-mm1.orig/ipc/sem.c	2007-09-21 10:33:50.000000000 +0200
> +++ linux-2.6.23-rc6-mm1/ipc/sem.c	2007-09-27 10:35:40.000000000 +0200
> @@ -80,7 +80,7 @@
>  #include <linux/audit.h>
>  #include <linux/capability.h>
>  #include <linux/seq_file.h>
> -#include <linux/mutex.h>
> +#include <linux/rwsem.h>
>  #include <linux/nsproxy.h>
>  
>  #include <asm/uaccess.h>
> @@ -148,7 +148,7 @@ void sem_exit_ns(struct ipc_namespace *n
>  	int next_id;
>  	int total, in_use;
>  
> -	mutex_lock(&sem_ids(ns).mutex);
> +	down_write(&sem_ids(ns).rw_mutex);
>  
>  	in_use = sem_ids(ns).in_use;
>  
> @@ -160,7 +160,7 @@ void sem_exit_ns(struct ipc_namespace *n
>  		freeary(ns, sma);
>  		total++;
>  	}
> -	mutex_unlock(&sem_ids(ns).mutex);
> +	up_write(&sem_ids(ns).rw_mutex);
>  
>  	kfree(ns->ids[IPC_SEM_IDS]);
>  	ns->ids[IPC_SEM_IDS] = NULL;
> @@ -174,6 +174,22 @@ void __init sem_init (void)
>  				IPC_SEM_IDS, sysvipc_sem_proc_show);
>  }
>  
> +/*
> + * This routine is called in the paths where the rw_mutex is held to protect
> + * access to the idr tree.
> + */
> +static inline struct sem_array *sem_lock_check_down(struct ipc_namespace *ns,
> +						int id)
> +{
> +	struct kern_ipc_perm *ipcp = ipc_lock_check_down(&sem_ids(ns), id);
> +
> +	return container_of(ipcp, struct sem_array, sem_perm);
> +}
> +
> +/*
> + * sem_lock_(check_) routines are called in the paths where the rw_mutex
> + * is not held.
> + */
>  static inline struct sem_array *sem_lock(struct ipc_namespace *ns, int id)
>  {
>  	struct kern_ipc_perm *ipcp = ipc_lock(&sem_ids(ns), id);
> @@ -233,7 +249,7 @@ static inline void sem_rmid(struct ipc_n
>   * @ns: namespace
>   * @params: ptr to the structure that contains key, semflg and nsems
>   *
> - * Called with sem_ids.mutex held
> + * Called with sem_ids.rw_mutex held (as a writer)
>   */
>  
>  static int newary(struct ipc_namespace *ns, struct ipc_params *params)
> @@ -290,7 +306,7 @@ static int newary(struct ipc_namespace *
>  
>  
>  /*
> - * Called with sem_ids.mutex and ipcp locked.
> + * Called with sem_ids.rw_mutex and ipcp locked.
>   */
>  static inline int sem_security(struct kern_ipc_perm *ipcp, int semflg)
>  {
> @@ -301,7 +317,7 @@ static inline int sem_security(struct ke
>  }
>  
>  /*
> - * Called with sem_ids.mutex and ipcp locked.
> + * Called with sem_ids.rw_mutex and ipcp locked.
>   */
>  static inline int sem_more_checks(struct kern_ipc_perm *ipcp,
>  				struct ipc_params *params)
> @@ -528,9 +544,9 @@ static int count_semzcnt (struct sem_arr
>  	return semzcnt;
>  }
>  
> -/* Free a semaphore set. freeary() is called with sem_ids.mutex locked and
> - * the spinlock for this semaphore set hold. sem_ids.mutex remains locked
> - * on exit.
> +/* Free a semaphore set. freeary() is called with sem_ids.rw_mutex locked
> + * as a writer and the spinlock for this semaphore set hold. sem_ids.rw_mutex
> + * remains locked on exit.
>   */
>  static void freeary(struct ipc_namespace *ns, struct sem_array *sma)
>  {
> @@ -615,7 +631,7 @@ static int semctl_nolock(struct ipc_name
>  		seminfo.semmnu = SEMMNU;
>  		seminfo.semmap = SEMMAP;
>  		seminfo.semume = SEMUME;
> -		mutex_lock(&sem_ids(ns).mutex);
> +		down_read(&sem_ids(ns).rw_mutex);
>  		if (cmd == SEM_INFO) {
>  			seminfo.semusz = sem_ids(ns).in_use;
>  			seminfo.semaem = ns->used_sems;
> @@ -624,7 +640,7 @@ static int semctl_nolock(struct ipc_name
>  			seminfo.semaem = SEMAEM;
>  		}
>  		max_id = ipc_get_maxid(&sem_ids(ns));
> -		mutex_unlock(&sem_ids(ns).mutex);
> +		up_read(&sem_ids(ns).rw_mutex);
>  		if (copy_to_user (arg.__buf, &seminfo, sizeof(struct seminfo))) 
>  			return -EFAULT;
>  		return (max_id < 0) ? 0: max_id;
> @@ -895,7 +911,7 @@ static int semctl_down(struct ipc_namesp
>  		if(copy_semid_from_user (&setbuf, arg.buf, version))
>  			return -EFAULT;
>  	}
> -	sma = sem_lock_check(ns, semid);
> +	sma = sem_lock_check_down(ns, semid);
>  	if (IS_ERR(sma))
>  		return PTR_ERR(sma);
>  
> @@ -976,9 +992,9 @@ asmlinkage long sys_semctl (int semid, i
>  		return err;
>  	case IPC_RMID:
>  	case IPC_SET:
> -		mutex_lock(&sem_ids(ns).mutex);
> +		down_write(&sem_ids(ns).rw_mutex);
>  		err = semctl_down(ns,semid,semnum,cmd,version,arg);
> -		mutex_unlock(&sem_ids(ns).mutex);
> +		up_write(&sem_ids(ns).rw_mutex);
>  		return err;
>  	default:
>  		return -EINVAL;
> Index: linux-2.6.23-rc6-mm1/ipc/shm.c
> ===================================================================
> --- linux-2.6.23-rc6-mm1.orig/ipc/shm.c	2007-09-21 10:34:25.000000000 +0200
> +++ linux-2.6.23-rc6-mm1/ipc/shm.c	2007-09-27 10:30:30.000000000 +0200
> @@ -35,7 +35,7 @@
>  #include <linux/capability.h>
>  #include <linux/ptrace.h>
>  #include <linux/seq_file.h>
> -#include <linux/mutex.h>
> +#include <linux/rwsem.h>
>  #include <linux/nsproxy.h>
>  #include <linux/mount.h>
>  
> @@ -83,8 +83,8 @@ static void __shm_init_ns(struct ipc_nam
>  }
>  
>  /*
> - * Called with shm_ids.mutex and the shp structure locked.
> - * Only shm_ids.mutex remains locked on exit.
> + * Called with shm_ids.rw_mutex (writer) and the shp structure locked.
> + * Only shm_ids.rw_mutex remains locked on exit.
>   */
>  static void do_shm_rmid(struct ipc_namespace *ns, struct shmid_kernel *shp)
>  {
> @@ -115,7 +115,7 @@ void shm_exit_ns(struct ipc_namespace *n
>  	int next_id;
>  	int total, in_use;
>  
> -	mutex_lock(&shm_ids(ns).mutex);
> +	down_write(&shm_ids(ns).rw_mutex);
>  
>  	in_use = shm_ids(ns).in_use;
>  
> @@ -127,7 +127,7 @@ void shm_exit_ns(struct ipc_namespace *n
>  		do_shm_rmid(ns, shp);
>  		total++;
>  	}
> -	mutex_unlock(&shm_ids(ns).mutex);
> +	up_write(&shm_ids(ns).rw_mutex);
>  
>  	kfree(ns->ids[IPC_SHM_IDS]);
>  	ns->ids[IPC_SHM_IDS] = NULL;
> @@ -141,6 +141,31 @@ void __init shm_init (void)
>  				IPC_SHM_IDS, sysvipc_shm_proc_show);
>  }
>  
> +/*
> + * shm_lock_(check_)down routines are called in the paths where the rw_mutex
> + * is held to protect access to the idr tree.
> + */
> +static inline struct shmid_kernel *shm_lock_down(struct ipc_namespace *ns,
> +						int id)
> +{
> +	struct kern_ipc_perm *ipcp = ipc_lock_down(&shm_ids(ns), id);
> +
> +	return container_of(ipcp, struct shmid_kernel, shm_perm);
> +}
> +
> +static inline struct shmid_kernel *shm_lock_check_down(
> +						struct ipc_namespace *ns,
> +						int id)
> +{
> +	struct kern_ipc_perm *ipcp = ipc_lock_check_down(&shm_ids(ns), id);
> +
> +	return container_of(ipcp, struct shmid_kernel, shm_perm);
> +}
> +
> +/*
> + * shm_lock_(check_) routines are called in the paths where the rw_mutex
> + * is not held.
> + */
>  static inline struct shmid_kernel *shm_lock(struct ipc_namespace *ns, int id)
>  {
>  	struct kern_ipc_perm *ipcp = ipc_lock(&shm_ids(ns), id);
> @@ -189,7 +214,7 @@ static void shm_open(struct vm_area_stru
>   * @ns: namespace
>   * @shp: struct to free
>   *
> - * It has to be called with shp and shm_ids.mutex locked,
> + * It has to be called with shp and shm_ids.rw_mutex (writer) locked,
>   * but returns with shp unlocked and freed.
>   */
>  static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
> @@ -220,9 +245,9 @@ static void shm_close(struct vm_area_str
>  	struct shmid_kernel *shp;
>  	struct ipc_namespace *ns = sfd->ns;
>  
> -	mutex_lock(&shm_ids(ns).mutex);
> +	down_write(&shm_ids(ns).rw_mutex);
>  	/* remove from the list of attaches of the shm segment */
> -	shp = shm_lock(ns, sfd->id);
> +	shp = shm_lock_down(ns, sfd->id);
>  	BUG_ON(IS_ERR(shp));
>  	shp->shm_lprid = task_tgid_vnr(current);
>  	shp->shm_dtim = get_seconds();
> @@ -232,7 +257,7 @@ static void shm_close(struct vm_area_str
>  		shm_destroy(ns, shp);
>  	else
>  		shm_unlock(shp);
> -	mutex_unlock(&shm_ids(ns).mutex);
> +	up_write(&shm_ids(ns).rw_mutex);
>  }
>  
>  static int shm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> @@ -353,7 +378,7 @@ static struct vm_operations_struct shm_v
>   * @ns: namespace
>   * @params: ptr to the structure that contains key, size and shmflg
>   *
> - * Called with shm_ids.mutex held
> + * Called with shm_ids.rw_mutex held as a writer.
>   */
>  
>  static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
> @@ -442,7 +467,7 @@ no_file:
>  }
>  
>  /*
> - * Called with shm_ids.mutex and ipcp locked.
> + * Called with shm_ids.rw_mutex and ipcp locked.
>   */
>  static inline int shm_security(struct kern_ipc_perm *ipcp, int shmflg)
>  {
> @@ -453,7 +478,7 @@ static inline int shm_security(struct ke
>  }
>  
>  /*
> - * Called with shm_ids.mutex and ipcp locked.
> + * Called with shm_ids.rw_mutex and ipcp locked.
>   */
>  static inline int shm_more_checks(struct kern_ipc_perm *ipcp,
>  				struct ipc_params *params)
> @@ -578,7 +603,7 @@ static inline unsigned long copy_shminfo
>  }
>  
>  /*
> - * Called with shm_ids.mutex held
> + * Called with shm_ids.rw_mutex held as a reader
>   */
>  static void shm_get_stat(struct ipc_namespace *ns, unsigned long *rss,
>  		unsigned long *swp)
> @@ -649,9 +674,9 @@ asmlinkage long sys_shmctl (int shmid, i
>  		if(copy_shminfo_to_user (buf, &shminfo, version))
>  			return -EFAULT;
>  
> -		mutex_lock(&shm_ids(ns).mutex);
> +		down_read(&shm_ids(ns).rw_mutex);
>  		err = ipc_get_maxid(&shm_ids(ns));
> -		mutex_unlock(&shm_ids(ns).mutex);
> +		up_read(&shm_ids(ns).rw_mutex);
>  
>  		if(err<0)
>  			err = 0;
> @@ -666,14 +691,14 @@ asmlinkage long sys_shmctl (int shmid, i
>  			return err;
>  
>  		memset(&shm_info,0,sizeof(shm_info));
> -		mutex_lock(&shm_ids(ns).mutex);
> +		down_read(&shm_ids(ns).rw_mutex);
>  		shm_info.used_ids = shm_ids(ns).in_use;
>  		shm_get_stat (ns, &shm_info.shm_rss, &shm_info.shm_swp);
>  		shm_info.shm_tot = ns->shm_tot;
>  		shm_info.swap_attempts = 0;
>  		shm_info.swap_successes = 0;
>  		err = ipc_get_maxid(&shm_ids(ns));
> -		mutex_unlock(&shm_ids(ns).mutex);
> +		up_read(&shm_ids(ns).rw_mutex);
>  		if(copy_to_user (buf, &shm_info, sizeof(shm_info))) {
>  			err = -EFAULT;
>  			goto out;
> @@ -786,8 +811,8 @@ asmlinkage long sys_shmctl (int shmid, i
>  		 *	Instead we set a destroyed flag, and then blow
>  		 *	the name away when the usage hits zero.
>  		 */
> -		mutex_lock(&shm_ids(ns).mutex);
> -		shp = shm_lock_check(ns, shmid);
> +		down_write(&shm_ids(ns).rw_mutex);
> +		shp = shm_lock_check_down(ns, shmid);
>  		if (IS_ERR(shp)) {
>  			err = PTR_ERR(shp);
>  			goto out_up;
> @@ -809,7 +834,7 @@ asmlinkage long sys_shmctl (int shmid, i
>  			goto out_unlock_up;
>  
>  		do_shm_rmid(ns, shp);
> -		mutex_unlock(&shm_ids(ns).mutex);
> +		up_write(&shm_ids(ns).rw_mutex);
>  		goto out;
>  	}
>  
> @@ -824,8 +849,8 @@ asmlinkage long sys_shmctl (int shmid, i
>  			err = -EFAULT;
>  			goto out;
>  		}
> -		mutex_lock(&shm_ids(ns).mutex);
> -		shp = shm_lock_check(ns, shmid);
> +		down_write(&shm_ids(ns).rw_mutex);
> +		shp = shm_lock_check_down(ns, shmid);
>  		if (IS_ERR(shp)) {
>  			err = PTR_ERR(shp);
>  			goto out_up;
> @@ -864,7 +889,7 @@ asmlinkage long sys_shmctl (int shmid, i
>  out_unlock_up:
>  	shm_unlock(shp);
>  out_up:
> -	mutex_unlock(&shm_ids(ns).mutex);
> +	up_write(&shm_ids(ns).rw_mutex);
>  	goto out;
>  out_unlock:
>  	shm_unlock(shp);
> @@ -1000,8 +1025,8 @@ invalid:
>  	fput(file);
>  
>  out_nattch:
> -	mutex_lock(&shm_ids(ns).mutex);
> -	shp = shm_lock(ns, shmid);
> +	down_write(&shm_ids(ns).rw_mutex);
> +	shp = shm_lock_down(ns, shmid);
>  	BUG_ON(IS_ERR(shp));
>  	shp->shm_nattch--;
>  	if(shp->shm_nattch == 0 &&
> @@ -1009,7 +1034,7 @@ out_nattch:
>  		shm_destroy(ns, shp);
>  	else
>  		shm_unlock(shp);
> -	mutex_unlock(&shm_ids(ns).mutex);
> +	up_write(&shm_ids(ns).rw_mutex);
>  
>  out:
>  	return err;
> 
> --
> 
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