From: Thomas Veerman <thomas@minix3.org>
Date: Fri, 9 Dec 2011 10:43:13 +0000 (+0000)
Subject: Discard process' pending request upon incoming PM request
X-Git-Tag: v3.2.0~178
X-Git-Url: http://zhaoyanbai.com/repos/%22http:/www.isc.org/icons/zpipe.c?a=commitdiff_plain;h=94da86cbeec0c6673400e63b759faf025b6b24e4;p=minix.git

Discard process' pending request upon incoming PM request

When a process wants something done from VFS, but VFS has no worker
threads available, the request is stored and executed later. However,
when PM also sends a request for that process at the same time, discard
the pending request from the process and give priority to PM. The request
PM sends is either an EXIT or a DUMPCORE request, so we're not interested
in executing the pending request anyway.
---

diff --git a/servers/avfs/main.c b/servers/avfs/main.c
index eccfc82a5..02deb4ce9 100644
--- a/servers/avfs/main.c
+++ b/servers/avfs/main.c
@@ -881,9 +881,15 @@ PRIVATE void service_pm()
 	okendpt(m_in.PM_PROC, &slot);
 	fp = &fproc[slot];
 
-	assert(!(fp->fp_flags & FP_PENDING));
-	fp->fp_job.j_m_in = m_in;
-	fp->fp_flags |= FP_PM_PENDING;
+	if (fp->fp_flags & FP_PENDING) {
+		/* This process has a request pending, but PM wants it gone.
+		 * Forget about the pending request and satisfy PM's request
+		 * instead. Note that a pending request AND an EXEC request
+		 * are mutually exclusive. Also, PM should send only one
+		 * request/process at a time.
+		 */
+		 assert(fp->fp_job.j_m_in.m_source != PM_PROC_NR);
+	}
 
         /* PM requests on behalf of a proc are handled after the system call
          * that might be in progress for that proc has finished. If the proc
@@ -891,9 +897,11 @@ PRIVATE void service_pm()
 	if (!(fp->fp_flags & FP_PENDING) && mutex_trylock(&fp->fp_lock) == 0) {
 		mutex_unlock(&fp->fp_lock);
 		worker_start(do_dummy);
-		yield();
         }
 
+	fp->fp_job.j_m_in = m_in;
+	fp->fp_flags |= FP_PM_PENDING;
+
 	return;
 
     case PM_FORK: