Process.exec with the linux posix_spawn mode has a bug

[forax at univ-mlv.fr]

Hi David,
spot on !

jspawnhelper had no execution permission (i overlook that in my installation process).

I wonder if the exception message can be improved to indicate that the issue is on jspawnhelper and not on the program i want to execute.

Thanks a lot,
Rémi

----- Mail original -----
> De: "David Lloyd" <david.lloyd at redhat.com>
> À: "Remi Forax" <forax at univ-mlv.fr>
> Cc: "core-libs-dev" <core-libs-dev at openjdk.java.net>, "Roger Riggs" <Roger.Riggs at oracle.com>, "Alan Bateman"
> <Alan.Bateman at oracle.com>
> Envoyé: Samedi 11 Mai 2019 17:14:56
> Objet: Re: Process.exec with the linux posix_spawn mode has a bug

> On Sat, May 11, 2019 at 9:49 AM Remi Forax <forax at univ-mlv.fr> wrote:
>>
>> I've seen a weird error on my CI [1] since the 15th of February when using the
>> jdk 13,
>> i was not able to run jshell* using the programmatic API (java tool) anymore.
>>
>> Yesterday, i took the time to track that issue and i believe i've found the root
>> cause, trying to execute the java launcher using ProcessBuilder.start() with
>> the jdk 13 sometimes fails with an i/o exception (errno 13) which is weird
>> because you are trying to execute the same process that the one you are
>> executing. Note that this is a spurious bug, I was not able to find the exact
>> condition that triggers that bug.
>> So sometime it works, sometime it doesn't.
> 
> Assuming you're running on Linux (given that the changeset only
> applies to Linux), errno 13 is EACCES which would indicate a
> filesystem permission issue.  Are you sure you have permission to
> execute `jspawnhelper` in your JVM installation?  Could there be an
> SELinux restriction in place?
> 
> Here's what the man page says:
> 
> ```
> 
>     [EACCES]           Search permission is denied for a component of
> the path prefix.
> 
> 
>     [EACCES]           The new process file is not an ordinary file.
> 
> 
>     [EACCES]           The new process file mode denies execute permission.
> 
> 
>     [EACCES]           The new process file is on a filesystem
> mounted with execution
> 
>                        disabled (MNT_NOEXEC in <sys/mount.h>).
> ```
> 
>> If i pass -Djdk.lang.Process.launchMechanism=fork (or vfork) when starting the
>> VM, the bug disappear meaning that the bug occurs when the VM is trying to use
>> posix_spawn, perhaps spawn is trying to do an optimization when you try to
>> execute the same process as the one you are running under some conditions ?
> 
> The posix_spawn approach executes an intermediate support process
> (`jspawnhelper`) which in turn executes the target process.  I believe
> there's an extensive discussion on the reasons for this in the
> `core-libs-dev` archive.
> 
> 
> --
> - DML