From 4d2bff5eb86e8d7b4a20934cccb93bdeebed3558 Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Tue, 30 Apr 2013 19:15:19 -0700 Subject: [PATCH] ipc: introduce obtaining a lockless ipc object Through ipc_lock() and therefore ipc_lock_check() we currently return the locked ipc object. This is not necessary for all situations and can, therefore, cause unnecessary ipc lock contention. Introduce analogous ipc_obtain_object() and ipc_obtain_object_check() functions that only lookup and return the ipc object. Both these functions must be called within the RCU read critical section. [akpm@linux-foundation.org: propagate the ipc_obtain_object() errno from ipc_lock()] Signed-off-by: Davidlohr Bueso Signed-off-by: Rik van Riel Reviewed-by: Chegu Vinod Acked-by: Michel Lespinasse Cc: Emmanuel Benisty Cc: Jason Low Cc: Peter Hurley Cc: Stanislav Kinsbursky Tested-by: Sedat Dilek Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/util.c | 71 +++++++++++++++++++++++++++++++++++++++++++----------- ipc/util.h | 2 ++ 2 files changed, 59 insertions(+), 14 deletions(-) diff --git a/ipc/util.c b/ipc/util.c index 03eadd8fb0fd..813804ebdeba 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -668,6 +668,28 @@ void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out) out->seq = in->seq; } +/** + * ipc_obtain_object + * @ids: ipc identifier set + * @id: ipc id to look for + * + * Look for an id in the ipc ids idr and return associated ipc object. + * + * Call inside the RCU critical section. + * The ipc object is *not* locked on exit. + */ +struct kern_ipc_perm *ipc_obtain_object(struct ipc_ids *ids, int id) +{ + struct kern_ipc_perm *out; + int lid = ipcid_to_idx(id); + + out = idr_find(&ids->ipcs_idr, lid); + if (!out) + return ERR_PTR(-EINVAL); + + return out; +} + /** * ipc_lock - Lock an ipc structure without rw_mutex held * @ids: IPC identifier set @@ -675,32 +697,53 @@ void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out) * * Look for an id in the ipc ids idr and lock the associated ipc object. * - * The ipc object is locked on exit. + * The ipc object is locked on successful exit. */ - struct kern_ipc_perm *ipc_lock(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); - } + out = ipc_obtain_object(ids, id); + if (IS_ERR(out)) + goto err1; spin_lock(&out->lock); - + /* ipc_rmid() may have already freed the ID while ipc_lock * was spinning: here verify that the structure is still valid */ - if (out->deleted) { - spin_unlock(&out->lock); - rcu_read_unlock(); - return ERR_PTR(-EINVAL); - } + if (!out->deleted) + return out; + spin_unlock(&out->lock); + out = ERR_PTR(-EINVAL); +err1: + rcu_read_unlock(); + return out; +} + +/** + * ipc_obtain_object_check + * @ids: ipc identifier set + * @id: ipc id to look for + * + * Similar to ipc_obtain_object() but also checks + * the ipc object reference counter. + * + * Call inside the RCU critical section. + * The ipc object is *not* locked on exit. + */ +struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id) +{ + struct kern_ipc_perm *out = ipc_obtain_object(ids, id); + + if (IS_ERR(out)) + goto out; + + if (ipc_checkid(out, id)) + return ERR_PTR(-EIDRM); +out: return out; } diff --git a/ipc/util.h b/ipc/util.h index ac1480a4efd1..bfc8d4ea6e46 100644 --- a/ipc/util.h +++ b/ipc/util.h @@ -123,6 +123,7 @@ void ipc_rcu_getref(void *ptr); void ipc_rcu_putref(void *ptr); struct kern_ipc_perm *ipc_lock(struct ipc_ids *, int); +struct kern_ipc_perm *ipc_obtain_object(struct ipc_ids *ids, int id); void kernel_to_ipc64_perm(struct kern_ipc_perm *in, struct ipc64_perm *out); void ipc64_perm_to_ipc_perm(struct ipc64_perm *in, struct ipc_perm *out); @@ -168,6 +169,7 @@ static inline void ipc_unlock(struct kern_ipc_perm *perm) } struct kern_ipc_perm *ipc_lock_check(struct ipc_ids *ids, int id); +struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id); int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids, struct ipc_ops *ops, struct ipc_params *params); void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids, -- 2.20.1