... and rewrite the function. For scenarios where the key is found and we end up just doing different routinary checks, we can downgrade the ids->rwsem and share it among concurrent readers. These checks include the following, which are all safe to share the lock:
ops->more_checks() >> sem_more_checks(), shm_more_checks() ipc_check_perms() >> ipcperms(),ops->associate() >> [lsm]_[ipctype]_associate() Signed-off-by: Davidlohr Bueso <[email protected]> --- ipc/util.c | 60 +++++++++++++++++++++++++++++++++--------------------------- 1 file changed, 33 insertions(+), 27 deletions(-) diff --git a/ipc/util.c b/ipc/util.c index e1b4c6d..fc5c655 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -183,7 +183,7 @@ void __init ipc_init_proc_interface(const char *path, const char *header, * ipc_findkey - find a key in an ipc identifier set * @ids: ipc identifier set * @key: key to find - * + * * Returns the locked pointer to the ipc structure if found or NULL * otherwise. If key is found ipc points to the owning ipc structure * @@ -375,48 +375,54 @@ static int ipc_check_perms(struct ipc_namespace *ns, * On success, the ipc id is returned. */ static int ipcget_public(struct ipc_namespace *ns, struct ipc_ids *ids, - struct ipc_ops *ops, struct ipc_params *params) + struct ipc_ops *ops, struct ipc_params *params) { struct kern_ipc_perm *ipcp; int flg = params->flg; - int err; + int err = 0; - /* - * Take the lock as a writer since we are potentially going to add - * a new entry + read locks are not "upgradable" - */ down_write(&ids->rwsem); ipcp = ipc_findkey(ids, params->key); - if (ipcp == NULL) { + + if (!ipcp) { /* key not used */ if (!(flg & IPC_CREAT)) err = -ENOENT; - else + else /* create new ipc object */ err = ops->getnew(ns, params); - } else { - /* ipc object has been locked by ipc_findkey() */ - - if (flg & IPC_CREAT && flg & IPC_EXCL) - err = -EEXIST; - else { - err = 0; - if (ops->more_checks) - err = ops->more_checks(ipcp, params); - if (!err) - /* - * ipc_check_perms returns the IPC id on - * success - */ - err = ipc_check_perms(ns, ipcp, ops, params); - } + + goto done_write; + } + + if ((flg & IPC_CREAT) && (flg & IPC_EXCL)) { + /* ipc object was locked by successful ipc_findkey() lookup */ ipc_unlock(ipcp); + err = -ENOENT; + + goto done_write; } - up_write(&ids->rwsem); + /* + * The key was found, so we will just perform routinary checks on + * ipc the object. Share the lock among other readers. + */ + downgrade_write(&ids->rwsem); + + if (ops->more_checks) + err = ops->more_checks(ipcp, params); + if (!err) + /* returns the IPC id on success */ + err = ipc_check_perms(ns, ipcp, ops, params); + + ipc_unlock(ipcp); + + up_read(&ids->rwsem); + return err; +done_write: + up_write(&ids->rwsem); return err; } - /** * ipc_rmid - remove an ipc identifier * @ids: ipc identifier set -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
