First, let me retract the proposed change,
it is not the right solution to the problem originally
reported.
Second, as a bit of explanation consider the code fragments below.
The high level processing calls openDoor which is willing to
retry
the operation as long as the error is flagged specifically
as a FileNotFoundException.
VirtualMachineImpl.java:72
VirtualMachineImpl.c:81
During my testing I had added a check VirtualMachineImpl.java:214
and when an IOException was detected made a call to
checkPermissions
to get more detailed information about the IOException. The error
I saw was an ENOENT from the stat call. And not the detailed
checks for
specific permissions issues (VirtualMachineImpl.c:143)
VirtualMachineImpl.c:118
VirtualMachineImpl.c:147
What I missed in the original proposed solution was a
FileNotFoundException
extends IOException. That means my delay and retry just
duplicates the higher
level retry around the openDoor call.
Third, the original error message logged in the bug report :
java.io.IOException: Permission denied
at jdk.attach/sun.tools.attach.VirtualMachineImpl.open(Native
Method)
had to have come from
VirtualMachineImpl.c:70
VirtualMachineImpl.c:84
which means the actual open call reported the file does exist
but the permissions do not allow the file to be accessed.
That also means the normal mechanism of removing leftover
java_pid files would not have cleaned up another user's
java_pid files.
=====
src/jdk.attach/solaris/classes/sun/tools/attach/VirtualMachineImpl.java:
...
67 // Opens the door file to the target VM. If
the file is not
68 // found it might mean that the attach
mechanism isn't started in the
69 // target VM so we attempt to start it and
retry.
70 try {
71 fd = openDoor(pid);
72 } catch (FileNotFoundException fnf1) {
73 File f = createAttachFile(pid);
74 try {
75 sigquit(pid);
76
77 // give the target VM time to start
the attach mechanism
78 final int delay_step = 100;
79 final long timeout = attachTimeout();
80 long time_spend = 0;
81 long delay = 0;
82 do {
83 // Increase timeout on each
attempt to reduce polling
84 delay += delay_step;
85 try {
86 Thread.sleep(delay);
87 } catch (InterruptedException x) { }
88 try {
89 fd = openDoor(pid);
90 } catch (FileNotFoundException
fnf2) {
91 // pass
92 }
93
94 time_spend += delay;
95 if (time_spend > timeout/2 && fd
== -1) {
96 // Send QUIT again to give
target VM the last chance to react
97 sigquit(pid);
98 }
99 } while (time_spend <= timeout && fd
== -1);
100 if (fd == -1) {
101 throw new
AttachNotSupportedException(
102 String.format("Unable to
open door %s: " +
103 "target process %d doesn't
respond within %dms " +
104 "or HotSpot VM not
loaded", socket_path, pid, time_spend));
105 }
...
212 // The door is attached to .java_pid<pid> in the
temporary directory.
213 private int openDoor(int pid) throws IOException {
214 socket_path = tmpdir + "/.java_pid" + pid;
215 fd = open(socket_path);
216
217 // Check that the file owner/permission to
avoid attaching to
218 // bogus process
219 try {
220 checkPermissions(socket_path);
221 } catch (IOException ioe) {
222 close(fd);
223 throw ioe;
224 }
225 return fd;
226 }
=====
src/jdk.attach/solaris/native/libattach/VirtualMachineImpl.c:
...
59 JNIEXPORT jint JNICALL
Java_sun_tools_attach_VirtualMachineImpl_open
60 (JNIEnv *env, jclass cls, jstring path)
61 {
62 jboolean isCopy;
63 const char* p = GetStringPlatformChars(env,
path, &isCopy);
64 if (p == NULL) {
65 return 0;
66 } else {
67 int fd;
68 int err = 0;
69
70 fd = open(p, O_RDWR);
71 if (fd == -1) {
72 err = errno;
73 }
74
75 if (isCopy) {
76 JNU_ReleaseStringPlatformChars(env,
path, p);
77 }
78
79 if (fd == -1) {
80 if (err == ENOENT) {
81 JNU_ThrowByName(env,
"java/io/FileNotFoundException", NULL);
82 } else {
83 char* msg = strdup(strerror(err));
84 JNU_ThrowIOException(env, msg);
85 if (msg != NULL) {
86 free(msg);
87 }
88 }
89 }
90 return fd;
91 }
92 }
...
99 JNIEXPORT void JNICALL
Java_sun_tools_attach_VirtualMachineImpl_checkPermissions
100 (JNIEnv *env, jclass cls, jstring path)
101 {
102 jboolean isCopy;
103 const char* p = GetStringPlatformChars(env,
path, &isCopy);
104 if (p != NULL) {
105 struct stat64 sb;
106 uid_t uid, gid;
107 int res;
108
109 memset(&sb, 0, sizeof(struct stat64));
110
111 /*
112 * Check that the path is owned by the
effective uid/gid of this
113 * process. Also check that group/other
access is not allowed.
114 */
115 uid = geteuid();
116 gid = getegid();
117
118 res = stat64(p, &sb);
119 if (res != 0) {
120 /* save errno */
121 res = errno;
122 }
123
124 if (res == 0) {
125 char msg[100];
126 jboolean isError = JNI_FALSE;
127 if (sb.st_uid != uid && uid != ROOT_UID) {
128 snprintf(msg, sizeof(msg),
129 "file should be owned by the
current user (which is %d) but is owned by %d", uid, sb.st_uid);
130 isError = JNI_TRUE;
131 } else if (sb.st_gid != gid && uid !=
ROOT_UID) {
132 snprintf(msg, sizeof(msg),
133 "file's group should be the
current group (which is %d) but the group is %d", gid, sb.st_gid);
134 isError = JNI_TRUE;
135 } else if ((sb.st_mode &
(S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH)) != 0) {
136 snprintf(msg, sizeof(msg),
137 "file should only be readable
and writable by the owner but has 0%03o access", sb.st_mode &
0777);
138 isError = JNI_TRUE;
139 }
140 if (isError) {
141 char buf[256];
142 snprintf(buf, sizeof(buf),
"well-known file %s is not secure: %s", p, msg);
143 JNU_ThrowIOException(env, buf);
144 }
145 } else {
146 char* msg = strdup(strerror(res));
147 JNU_ThrowIOException(env, msg);
148 if (msg != NULL) {
149 free(msg);
150 }
151 }
On 10/2/18, 6:23 PM, David Holmes wrote:
Minor correction: EPERM -> EACCES for Solaris
Hard to see how to get a transient EACCES when opening a file
... though as it is really a door I guess there could be
additional complexity.
David
On 3/10/2018 7:54 AM, Chris Plummer wrote:
On 10/2/18 2:38 PM, David Holmes wrote:
Chris,
On 3/10/2018 6:57 AM, Chris Plummer wrote:
On 10/2/18 1:44 PM, [email protected] wrote:
The general attach sequence ...
src/jdk.attach/solaris/classes/sun/tools/attach/VirtualMachineImpl.java
the attacher creates an attach_pid file in a directory
where the attachee is runnning
issues a signal to the attacheee
loops waiting for the java_pid file to be created
default timeout is 10 seconds
So getting a FileNotFoundException while in this loop is
OK, but IOException is not.
src/hotspot/os/solaris/attachListener_solaris.cpp
attachee creates the java_pid file
listens til the attacher opens the door
I'm don't think this is related, but JDK-8199811 made a
fix in attachListener_solaris.cpp to make it wait up to 10
seconds for initialization to complete before failing the
enqueue.
...
Not sure when a bare IOException is thrown rather than the
more specific FileNotFoundException.
Where is the IOException originating from? I wonder if the
issue is that the file is in the process of being created,
but is not fully created yet. Maybe it is there, but
owner/group/permissions have not been set yet, and this
results in an IOException instead of FileNotFoundException.
The exception is shown in the bug report:
[java.io.IOException: Permission denied
at
jdk.attach/sun.tools.attach.VirtualMachineImpl.open(Native
Method)
at
jdk.attach/sun.tools.attach.VirtualMachineImpl.openDoor(VirtualMachineImpl.java:215)
at
jdk.attach/sun.tools.attach.VirtualMachineImpl.<init>(VirtualMachineImpl.java:71)
at
jdk.attach/sun.tools.attach.AttachProviderImpl.attachVirtualMachine(AttachProviderImpl.java:58)
at
jdk.attach/com.sun.tools.attach.VirtualMachine.attach(VirtualMachine.java:207)
at
jdk.jcmd/sun.tools.jcmd.JCmd.executeCommandForPid(JCmd.java:114)
at jdk.jcmd/sun.tools.jcmd.JCmd.main(JCmd.java:98)
And if you look at the native code the EPERM from open will
cause IOException to be thrown.
./jdk.attach/solaris/native/libattach/VirtualMachineImpl.c
JNIEXPORT jint JNICALL
Java_sun_tools_attach_VirtualMachineImpl_open
(JNIEnv *env, jclass cls, jstring path)
{
jboolean isCopy;
const char* p = GetStringPlatformChars(env, path,
&isCopy);
if (p == NULL) {
return 0;
} else {
int fd;
int err = 0;
fd = open(p, O_RDWR);
if (fd == -1) {
err = errno;
}
if (isCopy) {
JNU_ReleaseStringPlatformChars(env, path, p);
}
if (fd == -1) {
if (err == ENOENT) {
JNU_ThrowByName(env,
"java/io/FileNotFoundException", NULL);
} else {
char* msg = strdup(strerror(err));
JNU_ThrowIOException(env, msg);
if (msg != NULL) {
free(msg);
}
We should add the path to the exception message.
Thanks David. So if EPERM is the error and a retry 100ms
later works, I think that supports my hypothesis that the
file is not quite fully created. So Gary's fix is probably
fine. The only other possible fix I can think of that
wouldn't require an explicit delay (or multiple retries) is
probably not worth the complexity. It would require that the
attachee create two files, and the attacher try to open the
second file first. When it either opens or returns EPERM,
you know the first file can safety be opened.
Chris
David
-----
Chris
On 10/2/18 4:11 PM, Chris Plummer wrote:
Can you summarize how the attach handshaking is suppose
to work? I'm just wondering why the attacher would ever
be looking for the file before the attachee has created
it. It seems a proper handshake would prevent this.
Maybe there's some sort of visibility issue where the
attachee has indeed created the file, but it is not
immediately visible to the attacher process.
Chris
On 10/2/18 12:27 PM, [email protected] wrote:
The problem reproduced pretty quickly.
I added a call to checkPermission and revealed the
"file not found" from the stat call when the IOException
was detected.
There has been some flakiness from the Solaris test
machines today,
so I'll continue with the testing a bit longer.
On 10/2/18 3:12 PM, Chris Plummer wrote:
Without the fix was this issue easy enough to
reproduce that you can be sure this is resolving it?
Chris
On 10/2/18 8:16 AM, Gary Adams wrote:
Solaris debug builds are failing tests that use the
attach interface.
An IOException is reported when the java_pid file is
not opened.
It appears that the attempt to attach is taking place
too quickly.
This workaround will allow the open operation to be
retried
after a short pause.
Webrev:
http://cr.openjdk.java.net/~gadams/8210337/webrev/
Issue:
https://bugs.openjdk.java.net/browse/JDK-8210337
Testing is in progress.
