Commit 370b262c authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Linus Torvalds

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: default avatarDavidlohr Bueso <>
Cc: Manfred Spraul <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent b5fa01a2
......@@ -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,
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)) {
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.
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