From: Davidlohr Bueso <dave@stgolabs.net>
To: akpm@linux-foundation.org, manfred@colorfullife.com
Cc: linux-kernel@vger.kernel.org, dave@stgolabs.net,
Davidlohr Bueso <dbueso@suse.de>
Subject: [PATCH -next 2/2] ipc/sem: avoid idr tree lookup for interrupted semop
Date: Wed, 9 Nov 2016 08:26:14 -0800 [thread overview]
Message-ID: <1478708774-28826-3-git-send-email-dave@stgolabs.net> (raw)
In-Reply-To: <1478708774-28826-1-git-send-email-dave@stgolabs.net>
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.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
ipc/sem.c | 37 +++++--------------------------------
1 file changed, 5 insertions(+), 32 deletions(-)
diff --git a/ipc/sem.c b/ipc/sem.c
index a5eaf517c8b4..11cdec301167 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -431,29 +431,6 @@ 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);
@@ -2016,16 +1993,12 @@ 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.
--
2.6.6
prev parent reply other threads:[~2016-11-09 16:27 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-09 16:26 [PATCH -next 0/2] ipc/sem: semop updates Davidlohr Bueso
2016-11-09 16:26 ` [PATCH -next 1/2] ipc/sem: simplify wait-wake loop Davidlohr Bueso
2016-11-09 16:26 ` Davidlohr Bueso [this message]
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