From: David van Moolenbroek <david@minix3.org>
Date: Sun, 6 Sep 2015 14:54:42 +0000 (+0200)
Subject: Improve asynsend support for process swapping
X-Git-Url: http://zhaoyanbai.com/repos/%22http:/static/doc/zpipe.c?a=commitdiff_plain;h=refs%2Fchanges%2F53%2F3153%2F1;p=minix.git

Improve asynsend support for process swapping

This resolves various system stalls while running testrelpol.

Change-Id: Ie70fc2dbcdb0a8c9e3800cc0df564be747e111ec
---

diff --git a/minix/kernel/system/do_privctl.c b/minix/kernel/system/do_privctl.c
index 1dd19423e..fc332a82e 100644
--- a/minix/kernel/system/do_privctl.c
+++ b/minix/kernel/system/do_privctl.c
@@ -120,6 +120,8 @@ int do_privctl(struct proc * caller, message * m_ptr)
 	priv(rp)->s_proc_nr = proc_nr;		/* reassociate process nr */
 
 	for (i=0; i< NR_SYS_CHUNKS; i++)		/* remove pending: */
+	      priv(rp)->s_asyn_pending.chunk[i] = 0;	/* - incoming asyn */
+	for (i=0; i< NR_SYS_CHUNKS; i++)		/*   messages */
 	      priv(rp)->s_notify_pending.chunk[i] = 0;	/* - notifications */
 	priv(rp)->s_int_pending = 0;			/* - interrupts */
 	(void) sigemptyset(&priv(rp)->s_sig_pending);	/* - signals */
diff --git a/minix/kernel/system/do_update.c b/minix/kernel/system/do_update.c
index ba6a8ab70..34c35f624 100644
--- a/minix/kernel/system/do_update.c
+++ b/minix/kernel/system/do_update.c
@@ -286,6 +286,7 @@ static void adjust_priv_slot(struct priv *privp, struct priv *from_privp)
 {
   /* Preserve privilege ids and non-privilege stuff in the priv structure. */
   privp->s_id = from_privp->s_id;
+  privp->s_asyn_pending = from_privp->s_asyn_pending;
   privp->s_notify_pending = from_privp->s_notify_pending;
   privp->s_int_pending = from_privp->s_int_pending;
   privp->s_sig_pending = from_privp->s_sig_pending;
diff --git a/minix/lib/libsys/sef_liveupdate.c b/minix/lib/libsys/sef_liveupdate.c
index 5becf0c2a..e326d28da 100644
--- a/minix/lib/libsys/sef_liveupdate.c
+++ b/minix/lib/libsys/sef_liveupdate.c
@@ -196,6 +196,37 @@ static void sef_lu_ready(int result)
    * Restore things back to normal and continue executing.
    */
   sef_lu_state_change(SEF_LU_STATE_NULL, 0);
+
+  /* Transfer of asynsend tables during live update is messy at best. The
+   * general idea is that the asynsend table is preserved during live update,
+   * so that messages never get lost. That means that 1) the new instance
+   * takes over the table from the old instance upon live update, and 2) the
+   * old instance takes over the table on rollback. Case 1 is not atomic:
+   * the new instance starts with no asynsend table, and after swapping slots,
+   * the old instance's table will no longer be looked at by the kernel. The
+   * new instance copies over the table from the old instance, and then calls
+   * senda_reload() to tell the kernel about the new location of the otherwise
+   * preserved table. Case 2 is different: the old instance cannot copy the
+   * table from the new instance, and so the kernel does that part, based on
+   * the table provided through the new instance's senda_reload(). However, if
+   * the new instance never got to the senda_reload() call, then the kernel
+   * also would not have been able to deliver any messages, and so the old
+   * instance's table can still be used as is. Now the problem. Because case 1
+   * is not atomic, there is a small window during which other processes may
+   * attempt to receive a message, based on the fact that their s_asyn_pending
+   * mask in the kernel has a bit set for the process being updated. Failing
+   * to find a matching message in the yet-missing table of the new process,
+   * the kernel will unset the s_asyn_pending bit. Now, normally the bit would
+   * be set again through the new instance's senda_reload() call. However, if
+   * the new instance rolls back instead, the old instance will have a message
+   * for the other process, but its s_asyn_pending bit will not be set. Thus,
+   * the message will never be delivered unless we call senda_reload() here.
+   * XXX TODO: the story is even more complicated, because based on the above
+   * story, copying back the table should never be necessary and never happen.
+   * My logs show it does happen for at least RS, which may indicate RS sends
+   * asynchronous messages in its initialization code.. -dcvmoole
+   */
+  senda_reload();
 }
 
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