Subject: + ipc-semc-make-semctlgetncntgetzcnt-standard-compliant.patch added to -mm tree
To: manfred@xxxxxxxxxxxxxxxx,davidlohr.bueso@xxxxxx,mtk.manpages@xxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Mon, 19 May 2014 15:46:51 -0700
The patch titled
Subject: ipc/sem.c: make semctl(,,{GETNCNT,GETZCNT}) standard compliant
has been added to the -mm tree. Its filename is
ipc-semc-make-semctlgetncntgetzcnt-standard-compliant.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/ipc-semc-make-semctlgetncntgetzcnt-standard-compliant.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/ipc-semc-make-semctlgetncntgetzcnt-standard-compliant.patch
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From: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Subject: ipc/sem.c: make semctl(,,{GETNCNT,GETZCNT}) standard compliant
SUSv4 clearly defines how semncnt and semzcnt must be calculated: A task
waits on exactly one semaphore: The semaphore from the first operation in
the sop array that cannot proceed.
The Linux implementation never followed the standard, it tried to count
all semaphores that might be the reason why a task sleeps.
This patch fixes that.
Note:
a) The implementation assumes that GETNCNT and GETZCNT are rare operations,
therefore the code counts them only on demand.
(If they wouldn't be rare, then the non-compliance would have
been found earlier)
b) compared to the initial version of the patch, the BUG_ONs were removed
and it was clarified that the new behavior conforms to SUS.
Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: Davidlohr Bueso <davidlohr.bueso@xxxxxx>
Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
ipc/sem.c | 34 +++++++++++++---------------------
1 file changed, 13 insertions(+), 21 deletions(-)
diff -puN ipc/sem.c~ipc-semc-make-semctlgetncntgetzcnt-standard-compliant ipc/sem.c
--- a/ipc/sem.c~ipc-semc-make-semctlgetncntgetzcnt-standard-compliant
+++ a/ipc/sem.c
@@ -993,38 +993,30 @@ static void do_smart_update(struct sem_a
}
/*
- * check_qop: Test how often a queued operation sleeps on the semaphore semnum
+ * check_qop: Test if a queued operation sleeps on the semaphore semnum
*/
static int check_qop(struct sem_array *sma, int semnum, struct sem_queue *q,
bool count_zero)
{
- struct sembuf *sops = q->sops;
- int nsops = q->nsops;
- int i, semcnt;
+ struct sembuf *sop = q->blocking;
- semcnt = 0;
+ if (sop->sem_num != semnum)
+ return 0;
- for (i = 0; i < nsops; i++) {
- if (sops[i].sem_num != semnum)
- continue;
- if (sops[i].sem_flg & IPC_NOWAIT)
- continue;
- if (count_zero && sops[i].sem_op == 0)
- semcnt++;
- if (!count_zero && sops[i].sem_op < 0)
- semcnt++;
- }
- return semcnt;
+ if (count_zero && sop->sem_op == 0)
+ return 1;
+ if (!count_zero && sop->sem_op < 0)
+ return 1;
+
+ return 0;
}
/* The following counts are associated to each semaphore:
* semncnt number of tasks waiting on semval being nonzero
* semzcnt number of tasks waiting on semval being zero
- * This model assumes that a task waits on exactly one semaphore.
- * Since semaphore operations are to be performed atomically, tasks actually
- * wait on a whole sequence of semaphores simultaneously.
- * The counts we return here are a rough approximation, but still
- * warrant that semncnt+semzcnt>0 if the task is on the pending queue.
+ *
+ * Per definition, a task waits only on the semaphore of the first semop
+ * that cannot proceed, even if additional operation would block, too.
*/
static int count_semcnt(struct sem_array *sma, ushort semnum,
bool count_zero)
_
Patches currently in -mm which might be from manfred@xxxxxxxxxxxxxxxx are
ipc-constify-ipc_ops.patch
ipc-shmc-check-for-ulong-overflows-in-shmat.patch
ipc-shmc-check-for-overflows-of-shm_tot.patch
ipc-shmc-check-for-integer-overflow-during-shmget.patch
ipc-shmc-increase-the-defaults-for-shmall-shmmax.patch
ipcshm-document-new-limits-in-the-uapi-header.patch
ipcshm-document-new-limits-in-the-uapi-header-v2.patch
ipcshm-document-new-limits-in-the-uapi-header-v3.patch
ipcmsg-use-current-state-helpers.patch
ipcmsg-move-some-msgq-ns-code-around.patch
ipcmsg-document-volatile-r_msg.patch
ipc-semc-bugfix-for-semctlgetzcnt.patch
ipc-semc-remove-code-duplication.patch
ipc-semc-change-perform_atomic_semop-parameters.patch
ipc-semc-store-which-operation-blocks-in-perform_atomic_semop.patch
ipc-semc-make-semctlgetncntgetzcnt-standard-compliant.patch
slab-leaks3-default-y.patch
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