The patch titled Subject: ipc: introduce obtaining a lockless ipc object has been removed from the -mm tree. Its filename was ipc-introduce-obtaining-a-lockless-ipc-object.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Davidlohr Bueso <davidlohr.bueso@xxxxxx> Subject: 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@xxxxxxxxxxxxxxxxxxxx: propagate the ipc_obtain_object() errno from ipc_lock()] Signed-off-by: Davidlohr Bueso <davidlohr.bueso@xxxxxx> Signed-off-by: Rik van Riel <riel@xxxxxxxxxx> Reviewed-by: Chegu Vinod <chegu_vinod@xxxxxx> Acked-by: Michel Lespinasse <walken@xxxxxxxxxx> Cc: Emmanuel Benisty <benisty.e@xxxxxxxxx> Cc: Jason Low <jason.low2@xxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> Cc: Stanislav Kinsbursky <skinsbursky@xxxxxxxxxxxxx> Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- ipc/util.c | 71 ++++++++++++++++++++++++++++++++++++++++----------- ipc/util.h | 2 + 2 files changed, 59 insertions(+), 14 deletions(-) diff -puN ipc/util.c~ipc-introduce-obtaining-a-lockless-ipc-object ipc/util.c --- a/ipc/util.c~ipc-introduce-obtaining-a-lockless-ipc-object +++ a/ipc/util.c @@ -669,38 +669,81 @@ void ipc64_perm_to_ipc_perm (struct ipc6 } /** + * 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 * @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. + * 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 -puN ipc/util.h~ipc-introduce-obtaining-a-lockless-ipc-object ipc/util.h --- a/ipc/util.h~ipc-introduce-obtaining-a-lockless-ipc-object +++ a/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 ker } 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, _ Patches currently in -mm which might be from davidlohr.bueso@xxxxxx are origin.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html