From b8fd99838435f9b420c3e848192bd43abc648b7f Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Fri, 17 Nov 2017 15:31:08 -0800 Subject: sysvipc: unteach ids->next_id for !CHECKPOINT_RESTORE Patch series "sysvipc: ipc-key management improvements". Here are a few improvements I spotted while eyeballing Guillaume's rhashtable implementation for ipc keys. The first and fourth patches are the interesting ones, the middle two are trivial. This patch (of 4): The next_id object-allocation functionality was introduced in commit 03f595668017 ("ipc: add sysctl to specify desired next object id"). Given that these new entries are _only_ exported under the CONFIG_CHECKPOINT_RESTORE option, there is no point for the common case to even know about ->next_id. As such rewrite ipc_buildid() such that it can do away with the field as well as unnecessary branches when adding a new identifier. The end result also better differentiates both cases, so the code ends up being cleaner; albeit the small duplications regarding the default case. [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/20170831172049.14576-2-dave@stgolabs.net Signed-off-by: Davidlohr Bueso Cc: Manfred Spraul Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/util.c | 60 +++++++++++++++++++++++++++++++++++++++++++++--------------- ipc/util.h | 5 ----- 2 files changed, 45 insertions(+), 20 deletions(-) (limited to 'ipc') diff --git a/ipc/util.c b/ipc/util.c index 79b30eee32cd..429c06bdb8ef 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -116,13 +116,15 @@ int ipc_init_ids(struct ipc_ids *ids) int err; ids->in_use = 0; ids->seq = 0; - ids->next_id = -1; init_rwsem(&ids->rwsem); err = rhashtable_init(&ids->key_ht, &ipc_kht_params); if (err) return err; idr_init(&ids->ipcs_idr); ids->tables_initialized = true; +#ifdef CONFIG_CHECKPOINT_RESTORE + ids->next_id = -1; +#endif return 0; } @@ -216,6 +218,46 @@ int ipc_get_maxid(struct ipc_ids *ids) return max_id; } +#ifdef CONFIG_CHECKPOINT_RESTORE +/* + * Specify desired id for next allocated IPC object. + */ +#define ipc_idr_alloc(ids, new) \ + idr_alloc(&(ids)->ipcs_idr, (new), \ + (ids)->next_id < 0 ? 0 : ipcid_to_idx((ids)->next_id),\ + 0, GFP_NOWAIT) + +static inline int ipc_buildid(int id, struct ipc_ids *ids, + struct kern_ipc_perm *new) +{ + if (ids->next_id < 0) { /* default, behave as !CHECKPOINT_RESTORE */ + new->seq = ids->seq++; + if (ids->seq > IPCID_SEQ_MAX) + ids->seq = 0; + } else { + new->seq = ipcid_to_seqx(ids->next_id); + ids->next_id = -1; + } + + return SEQ_MULTIPLIER * new->seq + id; +} + +#else +#define ipc_idr_alloc(ids, new) \ + idr_alloc(&(ids)->ipcs_idr, (new), 0, 0, GFP_NOWAIT) + +static inline int ipc_buildid(int id, struct ipc_ids *ids, + struct kern_ipc_perm *new) +{ + new->seq = ids->seq++; + if (ids->seq > IPCID_SEQ_MAX) + ids->seq = 0; + + return SEQ_MULTIPLIER * new->seq + id; +} + +#endif /* CONFIG_CHECKPOINT_RESTORE */ + /** * ipc_addid - add an ipc identifier * @ids: ipc identifier set @@ -234,7 +276,6 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size) kuid_t euid; kgid_t egid; int id, err; - int next_id = ids->next_id; if (size > IPCMNI) size = IPCMNI; @@ -254,9 +295,7 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size) new->cuid = new->uid = euid; new->gid = new->cgid = egid; - id = idr_alloc(&ids->ipcs_idr, new, - (next_id < 0) ? 0 : ipcid_to_idx(next_id), 0, - GFP_NOWAIT); + id = ipc_idr_alloc(ids, new); idr_preload_end(); if (id >= 0 && new->key != IPC_PRIVATE) { @@ -274,17 +313,8 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size) } ids->in_use++; + new->id = ipc_buildid(id, ids, new); - if (next_id < 0) { - new->seq = ids->seq++; - if (ids->seq > IPCID_SEQ_MAX) - ids->seq = 0; - } else { - new->seq = ipcid_to_seqx(next_id); - ids->next_id = -1; - } - - new->id = ipc_buildid(id, new->seq); return id; } diff --git a/ipc/util.h b/ipc/util.h index 579112d90016..0cd6201fe63a 100644 --- a/ipc/util.h +++ b/ipc/util.h @@ -146,11 +146,6 @@ extern struct msg_msg *load_msg(const void __user *src, size_t len); extern struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst); extern int store_msg(void __user *dest, struct msg_msg *msg, size_t len); -static inline int ipc_buildid(int id, int seq) -{ - return SEQ_MULTIPLIER * seq + id; -} - static inline int ipc_checkid(struct kern_ipc_perm *ipcp, int uid) { return uid / SEQ_MULTIPLIER != ipcp->seq; -- cgit v1.2.3-58-ga151 From 39c96a1b96a5991b1c9e79b85a8d74ef93b36026 Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Fri, 17 Nov 2017 15:31:11 -0800 Subject: sysvipc: duplicate lock comments wrt ipc_addid() The comment in msgqueues when using ipc_addid() is quite useful imo. Duplicate it for shm and semaphores. Link: http://lkml.kernel.org/r/20170831172049.14576-3-dave@stgolabs.net Signed-off-by: Davidlohr Bueso Cc: Manfred Spraul Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/sem.c | 1 + ipc/shm.c | 1 + 2 files changed, 2 insertions(+) (limited to 'ipc') diff --git a/ipc/sem.c b/ipc/sem.c index b2698ebdcb31..28a5c9f0be87 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -515,6 +515,7 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params) sma->sem_nsems = nsems; sma->sem_ctime = ktime_get_real_seconds(); + /* ipc_addid() locks sma upon success. */ retval = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni); if (retval < 0) { call_rcu(&sma->sem_perm.rcu, sem_rcu_free); diff --git a/ipc/shm.c b/ipc/shm.c index bd652755d32c..378c929194ce 100644 --- a/ipc/shm.c +++ b/ipc/shm.c @@ -601,6 +601,7 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params) shp->shm_file = file; shp->shm_creator = current; + /* ipc_addid() locks shp upon success. */ error = ipc_addid(&shm_ids(ns), &shp->shm_perm, ns->shm_ctlmni); if (error < 0) goto no_id; -- cgit v1.2.3-58-ga151 From ebf66799acfb5f52ada4ff96ecc9579867941ea9 Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Fri, 17 Nov 2017 15:31:15 -0800 Subject: sysvipc: properly name ipc_addid() limit parameter This is better understood as a limit, instead of size; exactly like the function comment indicates. Rename it. Link: http://lkml.kernel.org/r/20170831172049.14576-4-dave@stgolabs.net Signed-off-by: Davidlohr Bueso Cc: Manfred Spraul Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/util.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) (limited to 'ipc') diff --git a/ipc/util.c b/ipc/util.c index 429c06bdb8ef..e09bf76610ef 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -262,7 +262,7 @@ static inline int ipc_buildid(int id, struct ipc_ids *ids, * ipc_addid - add an ipc identifier * @ids: ipc identifier set * @new: new ipc permission set - * @size: limit for the number of used ids + * @limit: limit for the number of used ids * * Add an entry 'new' to the ipc ids idr. The permissions object is * initialised and the first free entry is set up and the id assigned @@ -271,16 +271,16 @@ static inline int ipc_buildid(int id, struct ipc_ids *ids, * * Called with writer ipc_ids.rwsem held. */ -int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size) +int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit) { kuid_t euid; kgid_t egid; int id, err; - if (size > IPCMNI) - size = IPCMNI; + if (limit > IPCMNI) + limit = IPCMNI; - if (!ids->tables_initialized || ids->in_use >= size) + if (!ids->tables_initialized || ids->in_use >= limit) return -ENOSPC; idr_preload(GFP_KERNEL); -- cgit v1.2.3-58-ga151 From 15df03c87983660a4d1eedb4541778592bd97684 Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Fri, 17 Nov 2017 15:31:18 -0800 Subject: sysvipc: make get_maxid O(1) again For a custom microbenchmark on a 3.30GHz Xeon SandyBridge, which calls IPC_STAT over and over, it was calculated that, on avg the cost of ipc_get_maxid() for increasing amounts of keys was: 10 keys: ~900 cycles 100 keys: ~15000 cycles 1000 keys: ~150000 cycles 10000 keys: ~2100000 cycles This is unsurprising as maxid is currently O(n). By having the max_id available in O(1) we save all those cycles for each semctl(_STAT) command, the idr_find can be expensive -- which some real (customer) workloads actually poll on. Note that this used to be the case, until commit 7ca7e564e04 ("ipc: store ipcs into IDRs"). The cost is the extra idr_find when doing RMIDs, but we simply go backwards, and should not take too many iterations to find the new value. [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/20170831172049.14576-5-dave@stgolabs.net Signed-off-by: Davidlohr Bueso Cc: Manfred Spraul Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/ipc_namespace.h | 1 + ipc/util.c | 43 +++++++++++++------------------------------ ipc/util.h | 21 ++++++++++++++++++--- 3 files changed, 32 insertions(+), 33 deletions(-) (limited to 'ipc') diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h index d7cf3a850853..b5630c8eb2f3 100644 --- a/include/linux/ipc_namespace.h +++ b/include/linux/ipc_namespace.h @@ -19,6 +19,7 @@ struct ipc_ids { bool tables_initialized; struct rw_semaphore rwsem; struct idr ipcs_idr; + int max_id; #ifdef CONFIG_CHECKPOINT_RESTORE int next_id; #endif diff --git a/ipc/util.c b/ipc/util.c index e09bf76610ef..ff045fec8d83 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -122,6 +122,7 @@ int ipc_init_ids(struct ipc_ids *ids) return err; idr_init(&ids->ipcs_idr); ids->tables_initialized = true; + ids->max_id = -1; #ifdef CONFIG_CHECKPOINT_RESTORE ids->next_id = -1; #endif @@ -188,36 +189,6 @@ static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key) return NULL; } -/** - * ipc_get_maxid - get the last assigned id - * @ids: ipc identifier set - * - * Called with ipc_ids.rwsem held. - */ -int ipc_get_maxid(struct ipc_ids *ids) -{ - struct kern_ipc_perm *ipc; - int max_id = -1; - int total, id; - - if (ids->in_use == 0) - return -1; - - if (ids->in_use == IPCMNI) - return IPCMNI - 1; - - /* Look for the last assigned id */ - total = 0; - for (id = 0; id < IPCMNI && total < ids->in_use; id++) { - ipc = idr_find(&ids->ipcs_idr, id); - if (ipc != NULL) { - max_id = id; - total++; - } - } - return max_id; -} - #ifdef CONFIG_CHECKPOINT_RESTORE /* * Specify desired id for next allocated IPC object. @@ -313,6 +284,9 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit) } ids->in_use++; + if (id > ids->max_id) + ids->max_id = id; + new->id = ipc_buildid(id, ids, new); return id; @@ -459,6 +433,15 @@ void ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp) ipc_kht_remove(ids, ipcp); ids->in_use--; ipcp->deleted = true; + + if (unlikely(lid == ids->max_id)) { + do { + lid--; + if (lid == -1) + break; + } while (!idr_find(&ids->ipcs_idr, lid)); + ids->max_id = lid; + } } /** diff --git a/ipc/util.h b/ipc/util.h index 0cd6201fe63a..89b8ec176fc4 100644 --- a/ipc/util.h +++ b/ipc/util.h @@ -13,6 +13,7 @@ #include #include +#include #define SEQ_MULTIPLIER (IPCMNI) @@ -99,9 +100,6 @@ void __init ipc_init_proc_interface(const char *path, const char *header, /* must be called with ids->rwsem acquired for writing */ int ipc_addid(struct ipc_ids *, struct kern_ipc_perm *, int); -/* must be called with ids->rwsem acquired for reading */ -int ipc_get_maxid(struct ipc_ids *); - /* must be called with both locks acquired. */ void ipc_rmid(struct ipc_ids *, struct kern_ipc_perm *); @@ -111,6 +109,23 @@ void ipc_set_key_private(struct ipc_ids *, struct kern_ipc_perm *); /* must be called with ipcp locked */ int ipcperms(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp, short flg); +/** + * ipc_get_maxid - get the last assigned id + * @ids: ipc identifier set + * + * Called with ipc_ids.rwsem held for reading. + */ +static inline int ipc_get_maxid(struct ipc_ids *ids) +{ + if (ids->in_use == 0) + return -1; + + if (ids->in_use == IPCMNI) + return IPCMNI - 1; + + return ids->max_id; +} + /* * For allocation that need to be freed by RCU. * Objects are reference counted, they start with reference count 1. -- cgit v1.2.3-58-ga151