RFR: 8197408: Bad pointer comparison and small cleanup in os_linux.cpp

[Robbin Ehn]

Hi Thomas, thanks for having a look.

On 2018-02-14 15:06, Thomas Stüfe wrote:
> Hi Robin,
> 
> Had a short look. Note that I cannot open the issue. Link is wrong, and the link in the source.patch is wrong too. So, I just looked at the webrev.
> 

Sorry bug is:
https://bugs.openjdk.java.net/browse/JDK-8197408

Inc here:
http://cr.openjdk.java.net/~rehn/8197408/v2/inc/webrev/
Full here:
http://cr.openjdk.java.net/~rehn/8197408/v2/full/webrev/

Comments on remarks below:

> Remarks:
> 
> -> This is a matter of taste but I prefer pointers to references for output variables. Makes the intent clearer at the calling site, and that way you could get rid of the /* output */ comment.

We had a debate about this, my opinion was that avoiding the NULL check makes it worth using a ref, but I see I'm pretty lonely in this camp so fixed.

> 
> -> in available_memory_container():
> Could we also add "using host value" to the logging in error case as you do in physical_memory_container()?

Fixed, and tried to improve the logs.

> 
> -> (Not part of your patch) Can OSContainer::memory_limit_in_bytes() actually ever return "OSCONTAINER_ERROR"? I may be wrong here but:
> 
> OSCONTAINER_ERROR = -2. /memory.limit_in_bytes gets returned as julong, so we have (julong)(-2). That gets compared with julong _unlimited_memory which is basically LONG_MAX, so signed long max, which should be smaller than (julong)(-2), or? So OSContainer::memory_limit_in_bytes() should always return -1 for both errors and the unlimited case.
> 

Manually tested this, it seems to work. The -2 gets promoted to unsigned in comparison.
We go from (jlong)-2 to (julong)ULONG_MAX-1 back to (jlong)-2.
Not obviously that it will always work. I will not touch that in this changeset.

> -> Can we:
> -  st->print("container_type: %s\n", p != NULL ? p : "failed");
> +  st->print_cr("container_type: %s", p != NULL ? p : "failed");
> ?

All of these use print + \n, you want me to just change this one or ?
I'll rather leave them alone.

> 
> -> char * OSContainer::container_type() - you free() that value but it is not strdup()ed.

Thanks for seeing this, copy-paste :)

> 
> (Btw I do not like that some functions return strduped values, some do not. If OSContainer::container_type() wants to return a static string, its return type should be at least const char*, not char*. They even added an explicit cast to nonconst char* .)

Changed to const.

Thanks, Robbin

> 
> Kind Regards, Thomas
> 
> 
> 
> On Wed, Feb 14, 2018 at 2:18 PM, Robbin Ehn <robbin.ehn at oracle.com <mailto:robbin.ehn at oracle.com>> wrote:
> 
>     Ping!
> 
>     /Robbin
> 
> 
>     On 2018-02-08 13:35, Robbin Ehn wrote:
> 
>         Hi David,
> 
>         On 02/08/2018 01:19 PM, David Holmes wrote:
> 
>             On 8/02/2018 10:08 PM, Robbin Ehn wrote:
> 
>                 Hi David,
> 
>                 On 02/08/2018 12:43 PM, David Holmes wrote:
> 
>                     Hi Robbin,
> 
>                     On 8/02/2018 7:03 PM, Robbin Ehn wrote:
> 
>                         Hi all,
> 
>                         There is a bad pointer comparison in os_linux.cpp while looking at that
> 
> 
>                     You seem to be missing the fact that OSContainer::cpu_cpuset_memory_nodes() can return a pointer or an error code.
> 
> 
>                 This is not true for macro:
>                 GET_CONTAINER_INFO_CPTR
> 
>                 As far I can see?
> 
> 
>             Sorry - you're right. I misread current code and misremembered what happened at the initial code review - where I'm sure this "pointer versus error code" issue was also flagged.
> 
>                 It returns:
>                 if (err != 0)
>                     return (return_type) NULL;
>                 or:
>                 return os::strdup(mems);
> 
>                 If you know a method that returns an integer in a char*, it's broken should be fixed.
> 
> 
>                         I saw some if statement were missing bracket, a lot of extra scopes and complexity in the scoping.
> 
> 
>                     You'd better check all this with Bob Vandette as its his container support code.
> 
> 
>                 Not sure what you mean. It passes container tests.
> 
> 
>             In what environment did you run the container tests? Most of the code you've been refactoring deals with various errors and misconfigurations that can occur.
> 
>             I'm sure Bob will want a chance to check the refactoring still does as he intended.
> 
> 
>         On mach5 all platforms with the container test (+ hotspot_tier1) and locally.
>         I said before, regarding containers, all Linux have cgroups configured so this logic always thinks we are in a container and does this logging and calculation.
> 
>         But no there is no tests for miss-configuration that I found.
> 
>         Added Bob!
> 
>         Thanks, Robbin
> 
> 
> 
>             Cheers,
>             David
>             -----
> 
> 
>                 Thanks, Robbin
> 
> 
>                     Cheers,
>                     David
> 
>                         Webrev:
>                         http://cr.openjdk.java.net/~rehn/8197408/webrev/ <http://cr.openjdk.java.net/~rehn/8197408/webrev/>
>                         Bug:
>                         http://cr.openjdk.java.net/~rehn/8197408/webrev/ <http://cr.openjdk.java.net/~rehn/8197408/webrev/>
> 
>                         Thanks, Robbin
> 
>