Fix SysV Semaphore Handling.

Updated by peter following KSE and Giant pushdown.
I've running with this patch for two week with no ill side effects.

PR:		kern/12014: Fix SysV Semaphore handling
Submitted by:	Peter Jeremy <peter.jeremy@alcatel.com.au>

1 files changed, 107 insertions, 26 deletions

diff --git a/lib/libc/sys/semop.2 b/lib/libc/sys/semop.2
index ac4e79c..4e80f7c 100644
--- a/lib/libc/sys/semop.2
+++ b/lib/libc/sys/semop.2
@@ -70,7 +70,11 @@ and
 .Fa sem_flg
 determine an operation to be performed on semaphore number
 .Fa sem_num
-in the set.  The values SEM_UNDO and IPC_NOWAIT may be
+in the set.  The values
+.Dv SEM_UNDO
+and
+.Dv IPC_NOWAIT
+may be
 .Em OR Ns 'ed
 into the
 .Fa sem_flg
@@ -80,16 +84,19 @@ The operation performed depends as follows on the value of
 .Fa sem_op :
 .\"
 .\" This section is based on the description of semop() in
-.\" Stevens, _Advanced Programming in the UNIX Environment_.
+.\" Stevens, _Advanced Programming in the UNIX Environment_,
+.\" and the semop(2) description in The Open Group Unix2 specification.
 .\"
 .Bl -bullet
 .It
 When
 .Fa sem_op
-is positive, the semaphore's value is incremented by
+is positive and the process has alter permission,
+the semaphore's value is incremented by
 .Fa sem_op Ns 's
-value.  If SEM_UNDO is specified, the semaphore's adjust on exit
-value is decremented by
+value.  If
+.Dv SEM_UNDO
+is specified, the semaphore's adjust on exit value is decremented by
 .Fa sem_op Ns 's
 value.  A positive value for
 .Fa sem_op
@@ -98,7 +105,8 @@ associated with the semaphore.
 .It
 The behavior when
 .Fa sem_op
-is negative depends on the current value of the semaphore:
+is negative and the process has alter permission,
+depends on the current value of the semaphore:
 .Bl -bullet
 .It
 If the current value of the semaphore is greater than or equal to
@@ -106,39 +114,54 @@ the absolute value of
 .Fa sem_op ,
 then the value is decremented by the absolute value of
 .Fa sem_op .
-If SEM_UNDO is specified, the semaphore's adjust on exit
+If
+.Dv SEM_UNDO
+is specified, the semaphore's adjust on exit
 value is incremented by the absolute value of
 .Fa sem_op .
 .It
-If the current value of the semaphore is less than
-.Fa sem_op Ns 's
-value, one of the following happens:
+If the current value of the semaphore is less than the absolute value of
+.Fa sem_op ,
+one of the following happens:
 .\" XXX a *second* sublist?
 .Bl -bullet
 .It
-If IPC_NOWAIT was specified, then
+If
+.Dv IPC_NOWAIT
+was specified, then
 .Fn semop
 returns immediately with a return value of
 .Er EAGAIN .
 .It
-If some other process has removed the semaphore with the IPC_RMID
+Otherwise, the calling process is put to sleep until one of the following
+conditions is satisfied:
+.\" XXX We already have two sublists, why not a third?
+.Bl -bullet
+.It
+Some other process removes the semaphore with the
+.Dv IPC_RMID
 option of
-.Fn semctl ,
-then
+.Fn semctl .
+In this case,
 .Fn semop
 returns immediately with a return value of
-.Er EINVAL .
+.Er EIDRM .
 .It
-Otherwise, the calling process is put to sleep until the semaphore's
+The process receives a signal that is to be caught.
+In this case, the process will resume execution as defined by
+.Fn sigaction .
+.It
+The semaphore's
 value is greater than or equal to the absolute value of
 .Fa sem_op .
 When this condition becomes true, the semaphore's value is decremented
 by the absolute value of
 .Fa sem_op ,
-and the semaphore's adjust on exit value is incremented by the
+the semaphore's adjust on exit value is incremented by the
 absolute value of
 .Fa sem_op .
 .El
+.El
 .Pp
 A negative value for
 .Fa sem_op
@@ -149,11 +172,42 @@ available.
 .It
 When
 .Fa sem_op
-is zero, the process waits for the semaphore's value to become zero.
-If it is already zero, the call to
+is zero and the process has read permission,
+one of the following will occur:
+.Bl -bullet
+.It
+If the current value of the semaphore is equal to zero
+then
 .Fn semop
-can return immediately.  Otherwise, the calling process is put to
-sleep until the semaphore's value becomes zero.
+can return immediately.
+.It
+If
+.Dv IPC_NOWAIT
+was specified, then
+.Fn semop
+returns immediately with a return value of
+.Er EAGAIN .
+.It
+Otherwise, the calling process is put to sleep until one of the following
+conditions is satisfied:
+.\" XXX Another nested sublists
+.Bl -bullet
+.It
+Some other process removes the semaphore with the
+.Dv IPC_RMID
+option of
+.Fn semctl .
+In this case,
+.Fn semop
+returns immediately with a return value of
+.Er EIDRM .
+.It
+The process receives a signal that is to be caught.
+In this case, the process will resume execution as defined by
+.Fn sigaction
+.It
+The semaphore's value becomes zero.
+.El
 .El
 .Pp
 For each semaphore a process has in use, the kernel maintains an
@@ -170,16 +224,20 @@ will fail if:
 .Bl -tag -width Er
 .It Bq Er EINVAL
 No semaphore set corresponds to
-.Fa semid .
+.Fa semid ,
+or the process would exceed the system-defined limit for the number of
+per-process SEM_UNDO structures.
 .It Bq Er EACCES
 Permission denied due to mismatch between operation and mode of
 semaphore set.
 .It Bq Er EAGAIN
-The semaphore's value was less than
-.Fa sem_op ,
-and IPC_NOWAIT was specified.
+The semaphore's value would have resulted in the process being put to sleep
+and
+.Dv IPC_NOWAIT
+was specified.
 .It Bq Er E2BIG
 Too many operations were specified.
+.Bq Dv SEMOPM
 .It Bq Er EFBIG
 .\"
 .\" I'd have thought this would be EINVAL, but the source says
@@ -187,7 +245,30 @@ Too many operations were specified.
 .\"
 .Fa sem_num
 was not in the range of valid semaphores for the set.
+.It Bq Er EIDRM
+The semaphore set was removed from the system.
+.It Bq Er EINTR
+The
+.Fn semop
+call was interrupted by a signal.
+.It Bq Er ENOSPC
+The system SEM_UNDO pool
+.Bq Dv SEMMNU
+is full.
+.It Bq Er ERANGE
+The requested operation would cause either
+the semaphore's current value
+.Bq Dv SEMVMX
+or its adjust on exit value
+.Bq Dv SEMAEM
+to exceed the system-imposed limits.
 .El
 .Sh SEE ALSO
 .Xr semctl 2 ,
-.Xr semget 2
+.Xr semget 2 ,
+.Xr sigaction 2
+.Sh BUGS
+.Fn Semop
+may block waiting for memory even if
+.Dv IPC_NOWAIT
+is specified.