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In accept1(), falloc() is called after the process has awoken, but prior

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to removing the connection from the queue. The problem here is that
falloc() may block and this would allow another process to accept the
connection instead. If this happens to leave the queue empty, then the
system will panic with an "accept: nothing queued".

Also changed a wakeup() to a wakeup_one() to avoid the "thundering herd"
problem on new connections in Apache (or any other application that has
multiple processes blocked in accept() for the same socket).
This commit is contained in:
David Greenman 1997-03-31 12:30:01 +00:00
parent 57862eed22
commit a91b87211d
3 changed files with 28 additions and 12 deletions
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6
sys/kern/uipc_sockbuf.c
View File

@ -31,7 +31,7 @@
* SUCH DAMAGE.
*
* @(#)uipc_socket2.c 8.1 (Berkeley) 6/10/93
* $Id: uipc_socket2.c,v 1.21 1997/02/19 19:15:43 wollman Exp $
* $Id: uipc_socket2.c,v 1.22 1997/02/24 20:30:57 wollman Exp $
*/
#include <sys/param.h>
@ -111,9 +111,9 @@ soisconnected(so)
TAILQ_INSERT_TAIL(&head->so_comp, so, so_list);
so->so_state |= SS_COMP;
sorwakeup(head);
wakeup((caddr_t)&head->so_timeo);
wakeup_one(&head->so_timeo);
} else {
wakeup((caddr_t)&so->so_timeo);
wakeup(&so->so_timeo);
sorwakeup(so);
sowwakeup(so);
}

6
sys/kern/uipc_socket2.c
View File

@ -31,7 +31,7 @@
* SUCH DAMAGE.
*
* @(#)uipc_socket2.c 8.1 (Berkeley) 6/10/93
* $Id: uipc_socket2.c,v 1.21 1997/02/19 19:15:43 wollman Exp $
* $Id: uipc_socket2.c,v 1.22 1997/02/24 20:30:57 wollman Exp $
*/
#include <sys/param.h>
@ -111,9 +111,9 @@ soisconnected(so)
TAILQ_INSERT_TAIL(&head->so_comp, so, so_list);
so->so_state |= SS_COMP;
sorwakeup(head);
wakeup((caddr_t)&head->so_timeo);
wakeup_one(&head->so_timeo);
} else {
wakeup((caddr_t)&so->so_timeo);
wakeup(&so->so_timeo);
sorwakeup(so);
sowwakeup(so);
}

28
sys/kern/uipc_syscalls.c
View File

@ -31,7 +31,7 @@
* SUCH DAMAGE.
*
* @(#)uipc_syscalls.c 8.4 (Berkeley) 2/21/94
* $Id: uipc_syscalls.c,v 1.22 1997/02/22 09:39:29 peter Exp $
* $Id: uipc_syscalls.c,v 1.23 1997/03/23 03:36:32 bde Exp $
*/
#include "opt_ktrace.h"
@ -208,20 +208,36 @@ accept1(p, uap, retval, compat)
splx(s);
return (error);
}
/*
* At this point we know that there is at least one connection
* ready to be accepted. Remove it from the queue prior to
* allocating the file descriptor for it since falloc() may
* block allowing another process to accept the connection
* instead.
*/
so = head->so_comp.tqh_first;
TAILQ_REMOVE(&head->so_comp, so, so_list);
head->so_qlen--;
fflag = fp->f_flag;
error = falloc(p, &fp, retval);
if (error) {
/*
* Probably ran out of file descriptors. Put the
* unaccepted connection back onto the queue and
* do another wakeup so some other process might
* have a chance at it.
*/
TAILQ_INSERT_HEAD(&head->so_comp, so, so_list);
head->so_qlen++;
wakeup_one(&head->so_timeo);
splx(s);
return (error);
}
so = head->so_comp.tqh_first;
if (so == NULL)
panic("accept: nothing queued");
TAILQ_REMOVE(&head->so_comp, so, so_list);
so->so_state &= ~SS_COMP;
so->so_head = NULL;
head->so_qlen--;
fp->f_type = DTYPE_SOCKET;
fp->f_flag = fflag;