From 3e148c79938aa39035669c1cfa3ff60722134535 Mon Sep 17 00:00:00 2001 From: Nadia Derbey Date: Thu, 18 Oct 2007 23:40:54 -0700 Subject: fix idr_find() locking 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 Acked-by: Jarek Poplawski Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/util.c | 78 +++++++++++++++++++++++++++++++++++++++++++++++++------------- 1 file changed, 62 insertions(+), 16 deletions(-) (limited to 'ipc/util.c') diff --git a/ipc/util.c b/ipc/util.c index fd29246dc3c..b42fbd58973 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -32,6 +32,7 @@ #include #include #include +#include #include @@ -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(const char *path, const char *header, * @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(struct ipc_ids *ids, key_t key) * 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, struct ipc_ids *ids, 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, struct ipc_ids *ids, * * 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 *ns, struct ipc_ids *ids, 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 *ns, struct ipc_ids *ids, } ipc_unlock(ipcp); } - mutex_unlock(&ids->mutex); + up_write(&ids->rw_mutex); return err; } @@ -415,8 +420,8 @@ int ipcget_public(struct ipc_namespace *ns, struct ipc_ids *ids, * @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 ipc64_perm *in, struct ipc_perm *out) } /** - * 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 ipc_ids *ids, int id) 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 ipc_ids *ids, int id) 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 seq_file *s, loff_t *pos) * 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_file *s, void *it) 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) -- cgit v1.2.3