From: David Smith <dsmith@redhat.com>
Date: Wed, 28 May 2014 15:54:57 +0000 (-0500)
Subject: Fixed PR16991 by avoiding an inifinte loop in task_dentry_path().
X-Git-Tag: release-2.6~107^2~32
X-Git-Url: https://sourceware.org/git/?a=commitdiff_plain;h=979929ed22092e90e33ca43fb8726e0248a082ad;p=systemtap.git

Fixed PR16991 by avoiding an inifinte loop in task_dentry_path().

* tapset/linux/dentry.stp (task_dentry_path): Return "UNKNOWN" for
  unmounted synthetic filesystems.
* testsuite/systemtap.base/task_dentry_path.exp: New file.
* testsuite/systemtap.base/task_dentry_path.sh: Ditto.
* testsuite/systemtap.base/task_dentry_path.stp: Ditto.
---

diff --git a/tapset/linux/dentry.stp b/tapset/linux/dentry.stp
index 0a564058c..db3eba038 100644
--- a/tapset/linux/dentry.stp
+++ b/tapset/linux/dentry.stp
@@ -170,6 +170,26 @@ function real_mount:long(vfsmnt:long)
  */
 function task_dentry_path:string(task:long,dentry:long,vfsmnt:long)
 {
+	/*
+	 * There are various synthetic filesystems that never get
+	 * mounted. Filesystems needing to implement special "root
+	 * names" do so with dentry->d_op->d_dname(). Unfortunately,
+	 * it isn't really safe for us to call
+	 * dentry->d_op->d_dname(). We can't really validate the
+	 * function pointer or know that it can be called safely in
+	 * the current context.
+	 *
+	 * Some pseudo inodes are mountable.  When they are mounted,
+	 * dentry == vfsmnt->mnt_root.  In that case, we'll just go
+	 * ahead and handle them normally.
+	 */
+	if (@defined(@cast(0, "dentry")->d_op->d_dname)
+	    && @cast(dentry, "dentry")->d_op
+	    && @cast(dentry, "dentry")->d_op->d_dname
+	    && (!__dentry_IS_ROOT(dentry)
+		|| dentry != @cast(vfsmnt, "vfsmount")->mnt_root))
+		return "UNKNOWN"
+
         root = & @cast(task, "task_struct")->fs->root
 
         while (1) {
diff --git a/testsuite/systemtap.base/task_dentry_path.exp b/testsuite/systemtap.base/task_dentry_path.exp
new file mode 100644
index 000000000..6e8d95084
--- /dev/null
+++ b/testsuite/systemtap.base/task_dentry_path.exp
@@ -0,0 +1,16 @@
+# This testcase tests the fix for PR16991 - infinite loop in
+# task_dentry_path. When task_dentry_path hit a dentry from an
+# unmounted synthentic filesystem, it would go into an infinite loop
+# (until killed by MAXACTION).
+
+set test "task_dentry_path"
+spawn stap $srcdir/$subdir/$test.stp -c "sh $srcdir/$subdir/$test.sh"
+set ok 0
+expect {
+    -timeout 150
+    -re {ERROR.*MAXACTION} { incr ok; exp_continue }
+    timeout { fail "$test (timeout)" }
+    eof { }
+}
+catch {close}; catch {wait}
+if {$ok == 1} { fail "$test ($ok)" } { pass "$test ($ok)" }
diff --git a/testsuite/systemtap.base/task_dentry_path.sh b/testsuite/systemtap.base/task_dentry_path.sh
new file mode 100644
index 000000000..398600cb6
--- /dev/null
+++ b/testsuite/systemtap.base/task_dentry_path.sh
@@ -0,0 +1,4 @@
+#!/bin/sh
+cd /tmp
+BASE="$(cd $(dirname ".")/../..; pwd -P)"
+echo $BASE
diff --git a/testsuite/systemtap.base/task_dentry_path.stp b/testsuite/systemtap.base/task_dentry_path.stp
new file mode 100644
index 000000000..7aeaec2ee
--- /dev/null
+++ b/testsuite/systemtap.base/task_dentry_path.stp
@@ -0,0 +1,18 @@
+global FSNOTIFY_EVENT_PATH = 1
+
+probe kernel.function("fsnotify") ?
+{
+    if (!target_set_pid(pid())) {
+	next
+    }
+    if ($data_is == FSNOTIFY_EVENT_PATH) {
+        path = task_dentry_path(task_current(), @cast($data, "path")->dentry,
+				@cast($data, "path")->mnt);
+        println(path);
+    }
+}
+
+probe begin
+{
+    printf("begin\n")
+}