diff options
| author | Davidlohr Bueso <dave@stgolabs.net> | 2016-12-14 15:06:49 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-12-14 16:04:08 -0800 |
| commit | 370b262c896e5565b271a3ea3abee4d0914ba443 (patch) | |
| tree | 7463704f20a1f8d00d717b34ca77a95b56a774fe | |
| parent | b5fa01a22e4ba9e3ca6de7cb94c3d21e42da449c (diff) | |
| download | linux-370b262c896e5565b271a3ea3abee4d0914ba443.tar.bz2 | |
ipc/sem: avoid idr tree lookup for interrupted semop
We can avoid the idr tree lookup (albeit possibly avoiding
idr_find_fast()) when being awoken in EINTR, as the semid will not
change in this context while blocked. Use the sma pointer directly and
take the sem_lock, then re-check for RMID races. We continue to
re-check the queue.status with the lock held such that we can detect
situations where we where are dealing with a spurious wakeup but another
task that holds the sem_lock updated the queue.status while we were
spinning for it. Once we take the lock it obviously won't change again.
Being the only caller, get rid of sem_obtain_lock() altogether.
Link: http://lkml.kernel.org/r/1478708774-28826-3-git-send-email-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | ipc/sem.c | 37 |
1 files changed, 5 insertions, 32 deletions
diff --git a/ipc/sem.c b/ipc/sem.c index a82c88d0900f..e08b94851922 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -414,29 +414,6 @@ static inline void sem_unlock(struct sem_array *sma, int locknum) * * The caller holds the RCU read lock. */ -static inline struct sem_array *sem_obtain_lock(struct ipc_namespace *ns, - int id, struct sembuf *sops, int nsops, int *locknum) -{ - struct kern_ipc_perm *ipcp; - struct sem_array *sma; - - ipcp = ipc_obtain_object_idr(&sem_ids(ns), id); - if (IS_ERR(ipcp)) - return ERR_CAST(ipcp); - - sma = container_of(ipcp, struct sem_array, sem_perm); - *locknum = sem_lock(sma, sops, nsops); - - /* ipc_rmid() may have already freed the ID while sem_lock - * was spinning: verify that the structure is still valid - */ - if (ipc_valid_object(ipcp)) - return container_of(ipcp, struct sem_array, sem_perm); - - sem_unlock(sma, *locknum); - return ERR_PTR(-EINVAL); -} - static inline struct sem_array *sem_obtain_object(struct ipc_namespace *ns, int id) { struct kern_ipc_perm *ipcp = ipc_obtain_object_idr(&sem_ids(ns), id); @@ -2000,16 +1977,12 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops, } rcu_read_lock(); - sma = sem_obtain_lock(ns, semid, sops, nsops, &locknum); - error = READ_ONCE(queue.status); + sem_lock(sma, sops, nsops); - /* - * Array removed? If yes, leave without sem_unlock(). - */ - if (IS_ERR(sma)) { - rcu_read_unlock(); - goto out_free; - } + if (!ipc_valid_object(&sma->sem_perm)) + goto out_unlock_free; + + error = READ_ONCE(queue.status); /* * If queue.status != -EINTR we are woken up by another process. |