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Make kevent(2) a cancellation point.

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Note that to cancel blocked kevent(2) call, changelist must be empty,
since we cannot cancel a call which already made changes to the
process state.  And in reverse, call which only makes changes to the
kqueue state, without waiting for an event, is not cancellable.  This
makes a natural usage model to migrate kqueue loop to support
cancellation, where existing single kevent(2) call must be split into
two: first uncancellable update of kqueue, then cancellable wait for
events.

Note that this is ABI-incompatible change, but it is believed that
there is no cancel-safe code that relies on kevent(2) not being a
cancellation point.  Option to preserve the ABI would be to keep
kevent(2) as is, but add new call with flags to specify cancellation
behaviour, which only value seems to add complications.

Suggested and reviewed by:	jilles
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
This commit is contained in:
Konstantin Belousov 2015-03-29 19:14:41 +00:00
parent fd78c994f5
commit b072e86d09
7 changed files with 116 additions and 3 deletions
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4
lib/libc/include/libc_private.h
View File

@ -221,6 +221,7 @@ enum {
INTERPOS__pthread_mutex_init_calloc_cb,
INTERPOS_spinlock,
INTERPOS_spinunlock,
INTERPOS_kevent,
INTERPOS_MAX
};
@ -293,6 +294,7 @@ void * __sys_freebsd6_mmap(void *, __size_t, int, int, int, int, __off_t);
struct aiocb;
struct fd_set;
struct iovec;
struct kevent;
struct msghdr;
struct pollfd;
struct rusage;
@ -315,6 +317,8 @@ int __sys_fsync(int);
__pid_t __sys_fork(void);
int __sys_ftruncate(int, __off_t);
int __sys_gettimeofday(struct timeval *, struct timezone *);
int __sys_kevent(int, const struct kevent *, int, struct kevent *,
int, const struct timespec *);
__off_t __sys_lseek(int, __off_t, int);
void *__sys_mmap(void *, __size_t, int, int, int, __off_t);
int __sys_msync(void *, __size_t, int);

1
lib/libc/sys/Makefile.inc
View File

@ -51,6 +51,7 @@ INTERPOSED = \
fcntl \
fsync \
fork \
kevent \
msync \
nanosleep \
open \

1
lib/libc/sys/interposing_table.c
View File

@ -75,6 +75,7 @@ interpos_func_t __libc_interposing[INTERPOS_MAX] = {
SLOT(_pthread_mutex_init_calloc_cb, _pthread_mutex_init_calloc_cb_stub),
SLOT(spinlock, __libc_spinlock_stub),
SLOT(spinunlock, __libc_spinunlock_stub),
SLOT(kevent, __sys_kevent),
};
#undef SLOT

53
lib/libc/sys/kevent.c Normal file
View File

@ -0,0 +1,53 @@
/*
* Copyright (c) 2015 The FreeBSD Foundation.
* All rights reserved.
*
* Portions of this software were developed by Konstantin Belousov
* under sponsorship from the FreeBSD Foundation.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice(s), this list of conditions and the following disclaimer as
* the first lines of this file unmodified other than the possible
* addition of one or more copyright notices.
* 2. Redistributions in binary form must reproduce the above copyright
* notice(s), this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
* BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
* OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/types.h>
#include <sys/event.h>
#include <sys/time.h>
#include "libc_private.h"
__weak_reference(__sys_kevent, __kevent);
#pragma weak kevent
int
kevent(int kq, const struct kevent *changelist, int nchanges,
struct kevent *eventlist, int nevents, const struct timespec *timeout)
{
return (((int (*)(int, const struct kevent *, int,
struct kevent *, int, const struct timespec *))
__libc_interposing[INTERPOS_kevent])(kq, changelist, nchanges,
eventlist, nevents, timeout));
}

25
lib/libc/sys/kqueue.2
View File

@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd July 18, 2014
.Dd March 29, 2015
.Dt KQUEUE 2
.Os
.Sh NAME
@ -41,7 +41,7 @@
.Fn kqueue "void"
.Ft int
.Fn kevent "int kq" "const struct kevent *changelist" "int nchanges" "struct kevent *eventlist" "int nevents" "const struct timespec *timeout"
.Fn EV_SET "&kev" ident filter flags fflags data udata
.Fn EV_SET "kev" ident filter flags fflags data udata
.Sh DESCRIPTION
The
.Fn kqueue
@ -550,6 +550,16 @@ On return,
.Va fflags
contains the users defined flags in the lower 24 bits.
.El
.Sh CANCELLATION BEHAVIOUR
If
.Fa nevents
is non-zero, i.e. the function is potentially blocking, the call
is a cancellation point.
Otherwise, i.e. if
.Fa nevents
is zero, the call is not cancellable.
Cancellation can only occur before any changes are made to the kqueue,
or when the call was blocked and no changes to the queue were requested.
.Sh RETURN VALUES
The
.Fn kqueue
@ -620,6 +630,8 @@ The specified descriptor is invalid.
.It Bq Er EINTR
A signal was delivered before the timeout expired and before any
events were placed on the kqueue for return.
.It Bq Er EINTR
A cancellation request was delivered to the thread, but not yet handled.
.It Bq Er EINVAL
The specified time limit or filter is invalid.
.It Bq Er ENOENT
@ -634,6 +646,14 @@ sysctl.
.It Bq Er ESRCH
The specified process to attach to does not exist.
.El
.Pp
When
.Fn kevent
call fails with
.Er EINTR
error, all changes in the
.Fa changelist
have been applied.
.Sh SEE ALSO
.Xr aio_error 2 ,
.Xr aio_read 2 ,
@ -643,6 +663,7 @@ The specified process to attach to does not exist.
.Xr select 2 ,
.Xr sigaction 2 ,
.Xr write 2 ,
.Xr pthread_setcancelstate 3 ,
.Xr signal 3
.Sh HISTORY
The

24
lib/libthr/thread/thr_syscalls.c
View File

@ -341,6 +341,29 @@ __thr_pselect(int count, fd_set *rfds, fd_set *wfds, fd_set *efds,
return (ret);
}
static int
__thr_kevent(int kq, const struct kevent *changelist, int nchanges,
struct kevent *eventlist, int nevents, const struct timespec *timeout)
{
struct pthread *curthread;
int ret;
if (nevents == 0) {
/*
* No blocking, do not make the call cancellable.
*/
return (__sys_kevent(kq, changelist, nchanges, eventlist,
nevents, timeout));
}
curthread = _get_curthread();
_thr_cancel_enter(curthread);
ret = __sys_kevent(kq, changelist, nchanges, eventlist, nevents,
timeout);
_thr_cancel_leave(curthread, ret == -1 && nchanges == 0);
return (ret);
}
/*
* Cancellation behavior:
* Thread may be canceled at start, but if the system call got some data,
@ -599,6 +622,7 @@ __thr_interpose_libc(void)
SLOT(writev);
SLOT(spinlock);
SLOT(spinunlock);
SLOT(kevent);
#undef SLOT
*(__libc_interposing_slot(
INTERPOS__pthread_mutex_init_calloc_cb)) =

11
share/man/man3/pthread_testcancel.3
View File

@ -1,5 +1,5 @@
.\" $FreeBSD$
.Dd June 11, 2013
.Dd March 29, 2015
.Dt PTHREAD_TESTCANCEL 3
.Os
.Sh NAME
@ -107,6 +107,7 @@ functions:
.Fn close ,
.Fn creat ,
.Fn fsync ,
.Fn kevent ,
.Fn mq_receive ,
.Fn mq_send ,
.Fn mq_timedreceive ,
@ -147,12 +148,20 @@ functions:
.Fn waitpid ,
.Fn write ,
.Fn writev .
.Pp
The
.Fn fcntl
function is a cancellation point if
.Fa cmd
is
.Dv F_SETLKW .
.Pp
The
.Fn kevent
function is a cancellation point if it is potentially blocking,
i.e. when the
.Fa nevents
argument is non-zero.
.Sh RETURN VALUES
If successful, the
.Fn pthread_setcancelstate