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hurd: Fix pselect atomicity

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In case the signal arrives before the __mach_msg call, we need to catch
between the sigprocmask call and the __mach_msg call.  Let's just reuse
the support for sigsuspend to make the signal send a message that
our __mach_msg call will just receive.

* hurd/hurdselect.c (_hurd_select): Add sigport and ss variables. When
sigmask is not NULL, create a sigport port and register as
ss->suspended.  Add it to the portset.  When we receive a message on it,
set error to EINTR.  Clean up sigport and portset appropriately.

* hurd/hurdsig.c (wake_sigsuspend): Note that pselect also uses it.
This commit is contained in:
Samuel Thibault 2020-05-27 23:42:24 +00:00
parent 31563b6841
commit f901178749
2 changed files with 70 additions and 10 deletions
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76
hurd/hurdselect.c
View File

@ -48,7 +48,7 @@ _hurd_select (int nfds,
const struct timespec *timeout, const sigset_t *sigmask)
{
int i;
mach_port_t portset;
mach_port_t portset, sigport;
int got, ready;
error_t err;
fd_set rfds, wfds, xfds;
@ -66,6 +66,7 @@ _hurd_select (int nfds,
int error;
} d[nfds];
sigset_t oset;
struct hurd_sigstate *ss;
union typeword /* Use this to avoid unkosher casts. */
{
@ -115,8 +116,30 @@ _hurd_select (int nfds,
reply_msgid = IO_SELECT_TIMEOUT_REPLY_MSGID;
}
if (sigmask && __sigprocmask (SIG_SETMASK, sigmask, &oset))
return -1;
if (sigmask)
{
/* Add a port to the portset for the case when we get the signal even
before calling __mach_msg. */
sigport = __mach_reply_port ();
ss = _hurd_self_sigstate ();
_hurd_sigstate_lock (ss);
/* And tell the signal thread to message us when a signal arrives. */
ss->suspended = sigport;
_hurd_sigstate_unlock (ss);
if (__sigprocmask (SIG_SETMASK, sigmask, &oset))
{
_hurd_sigstate_lock (ss);
ss->suspended = MACH_PORT_NULL;
_hurd_sigstate_unlock (ss);
__mach_port_destroy (__mach_task_self (), sigport);
return -1;
}
}
else
sigport = MACH_PORT_NULL;
if (pollfds)
{
@ -188,6 +211,8 @@ _hurd_select (int nfds,
d[i].io_port);
__mutex_unlock (&_hurd_dtable_lock);
HURD_CRITICAL_END;
if (sigmask)
__sigprocmask (SIG_SETMASK, &oset, NULL);
errno = err;
return -1;
}
@ -277,9 +302,14 @@ _hurd_select (int nfds,
/* Send them all io_select request messages. */
if (firstfd == -1)
/* But not if there were no ports to deal with at all.
We are just a pure timeout. */
portset = __mach_reply_port ();
{
if (sigport == MACH_PORT_NULL)
/* But not if there were no ports to deal with at all.
We are just a pure timeout. */
portset = __mach_reply_port ();
else
portset = sigport;
}
else
{
portset = MACH_PORT_NULL;
@ -298,7 +328,7 @@ _hurd_select (int nfds,
ts, type);
if (!err)
{
if (firstfd == lastfd)
if (firstfd == lastfd && sigport == MACH_PORT_NULL)
/* When there's a single descriptor, we don't need a
portset, so just pretend we have one, but really
use the single reply port. */
@ -329,6 +359,16 @@ _hurd_select (int nfds,
}
_hurd_port_free (&d[i].cell->port, &d[i].ulink, d[i].io_port);
}
if (got == 0 && sigport != MACH_PORT_NULL)
{
if (portset == MACH_PORT_NULL)
/* Create the portset to receive the signal message on. */
__mach_port_allocate (__mach_task_self (), MACH_PORT_RIGHT_PORT_SET,
&portset);
/* Put the signal reply port in the port set. */
__mach_port_move_member (__mach_task_self (), sigport, portset);
}
}
/* GOT is the number of replies (or errors), while READY is the number of
@ -404,6 +444,16 @@ _hurd_select (int nfds,
{ MACH_MSG_TYPE_INTEGER_T, sizeof (integer_t) * 8, 1, 1, 0, 0 }
};
#endif
if (sigport != MACH_PORT_NULL && sigport == msg.head.msgh_local_port)
{
/* We actually got interrupted by a signal before
__mach_msg; poll for further responses and then
return quickly. */
err = EINTR;
goto poll;
}
if (msg.head.msgh_id == reply_msgid
&& msg.head.msgh_size >= sizeof msg.error
&& !(msg.head.msgh_bits & MACH_MSGH_BITS_COMPLEX)
@ -492,7 +542,17 @@ _hurd_select (int nfds,
for (i = firstfd; i <= lastfd; ++i)
if (d[i].reply_port != MACH_PORT_NULL)
__mach_port_destroy (__mach_task_self (), d[i].reply_port);
if (firstfd == -1 || (firstfd != lastfd && portset != MACH_PORT_NULL))
if (sigport != MACH_PORT_NULL)
{
_hurd_sigstate_lock (ss);
ss->suspended = MACH_PORT_NULL;
_hurd_sigstate_unlock (ss);
__mach_port_destroy (__mach_task_self (), sigport);
}
if ((firstfd == -1 && sigport == MACH_PORT_NULL)
|| ((firstfd != lastfd || sigport != MACH_PORT_NULL) && portset != MACH_PORT_NULL))
/* Destroy PORTSET, but only if it's not actually the reply port for a
single descriptor (in which case it's destroyed in the previous loop;
not doing it here is just a bit more efficient). */

4
hurd/hurdsig.c
View File

@ -564,8 +564,8 @@ abort_all_rpcs (int signo, struct machine_thread_all_state *state, int live)
}
}
/* Wake up any sigsuspend call that is blocking SS->thread. SS must be
locked. */
/* Wake up any sigsuspend or pselect call that is blocking SS->thread. SS must
be locked. */
static void
wake_sigsuspend (struct hurd_sigstate *ss)
{